Check out our New Publishers' Select for Free Articles

Atmospheric Environment (v.43, #3)

Editorial board (pp. i).

Absence of trends in relative risk estimates for the association between Black Smoke and daily mortality over a 34 years period in The Netherlands by Paul Fischer; Caroline Ameling; Marten Marra; Flemming R. Cassee (pp. 481-485).

A major issue in air pollution epidemiology is whether the associations that are found in the statistical analyses on the health effects of air pollution reflect real causal associations of single components or mixtures thereof, or just reflect statistical associations that are mainly the result of the high correlation between the separate components, one of them being the true causal factor.In a previous analysis on the relationship between daily SO₂ levels and daily mortality in The Netherlands [Buringh, E., Fischer, P., Hoek, G., 2000. Is SO₂ a causative factor for the PM-associated mortality risks in The Netherlands? Inhal. Toxicol. 12 (Suppl. 1), 55–60.], it was shown that the statistical significant association between daily variation in SO₂ and daily mortality did not reflect a causal relation. Black Smoke levels in The Netherlands have decreased 4-fold during the 34 years in the period 1972–2006 (annual average from 27μgm⁻³ to 6μgm⁻³). This large decrease in concentrations enabled us to use the same approach for this component as was done earlier for SO₂ to assess whether a decreasing trend in Black Smoke levels in The Netherlands is associated with an increasing trend in mortality relative risks or not.We used daily averaged Black Smoke (BS) data from 1972 to 2006. In the first two decades (1970–1990) only sparse data were available. Based on the availability of the data, we selected data from 1972 to 1974 and from 1982 to 1984 because during these two periods continuous daily measurement series were available. For the later years (1989–2006) data covering the whole of The Netherlands were available, giving a total of 24 years of daily data. Data on daily total mortality counts (excluding external causes), cardiovascular mortality and respiratory mortality for the whole population of The Netherlands were analyzed with regard to daily Black Smoke levels using generalized additive Poisson regression models (GAM). Period specific relative risk estimates were compared and differences in estimates between periods were evaluated.We found no consistent increase in relative risks for daily total and cause-specific mortality over time, despite the decreasing trend in the Black Smoke levels in The Netherlands. Average relative risks for total mortality varied over the different periods from 0.997 per 10μgm⁻³ daily Black Smoke to 1.010 per 10μgm⁻³. Average relative risks for cardiovascular mortality varied from 0.988 per 10μgm⁻³ to 1.010 per 10μgm⁻³ and for respiratory mortality from 1.000 to 1.010 per 10μgm⁻³. For weekly averaged concentrations the average relative risks for total mortality varied over the different periods from 1.004 per 10μgm⁻³ Black Smoke to 1.018 per 10μgm⁻³. Average relative risks for cardiovascular mortality varied from 1.003 per 10μgm⁻³ to 1.016 per 10 μgm⁻³ and for respiratory mortality from 1.000 to 1.050 per 10μgm⁻³.The result of our analyses suggests that Black Smoke cannot be excluded as a potential causal agent because relative risks over time show no increasing trend despite the decreasing trend in Black Smoke concentrations.

Keywords: Black Smoke; Mortality; Time trend; Causality

Influence of tobacco smoke on the elemental composition of indoor particles of different sizes by K. Slezakova; M.C. Pereira; M.C. Alvim-Ferraz (pp. 486-493).

Tobacco smoking is one of the greatest sources of indoor inhalable (PM₁₀) particles. In the past, the studies conducted on indoor particulates were mostly related to PM₁₀, however in the last decade respirable particles (PM_2.5) and even smaller particles (PM₁) began to be more important as they penetrate deeper in the respiratory system, causing severe health effects. Therefore, more information on fine particles is needed. Aiming to evaluate the impact of tobacco smoke on public health, this work evaluates the influence of tobacco smoke on the characteristics of PM₁₀, PM_2.5, and PM₁ considering concentration and elemental composition. Samples were collected at sites influenced by tobacco smoke, as well as at reference sites, using low-volume samplers; the element analyses were performed by proton induced X-ray emission (PIXE); Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Br, Cd, I, Ba, La, Ce and Pb were quantified. At the sites influenced by tobacco smoke concentrations were 270–560% higher for PM₁₀ and 320–680% higher for PM_2.5 than at reference sites. Tobacco smoke increased the total concentrations of five carcinogenic elements (Cr, Ni, As, Cd and Pb) 1100–2400% for PM₁₀ and 840–2200% for PM_2.5. The elements associated with tobacco smoke (S, K, Cr, Ni, Zn, As, Cd and Pb) were predominantly present in the fine fraction; the elements mostly originating from building erosion (Mg, Al, Si and Ca) predominantly occurred in the coarse particles. The analysis of enrichment factors confirmed that tobacco smoking mainly influenced the composition of the fine fraction of particles; as these smaller particles have a strong influence on health, these conclusions are relevant for the development of strategies to protect public health.

Keywords: PM; ₁₀; PM; _2.5; PIXE; Tobacco smoke; Elemental composition

Improved space–time forecasting of next day ozone concentrations in the eastern US by Sujit K. Sahu; Stan Yip; David M. Holland (pp. 494-501).

There is an urgent need to provide accurate air quality information and forecasts to the general public and environmental health decision-makers. This paper develops a hierarchical space–time model for daily 8-h maximum ozone concentration (O₃) data covering much of the eastern United States. The model combines observed data and forecast output from a computer simulation model known as the Eta Community Multi-scale Air Quality (CMAQ) forecast model in a very flexible, yet computationally fast way, so that the next day forecasts can be computed in real-time operational mode. The model adjusts for spatio-temporal biases in the Eta CMAQ forecasts and avoids a change of support problem often encountered in data fusion settings where real data have been observed at point level monitoring sites, but the forecasts from the computer model are provided at grid cell levels. The model is validated with a large amount of set-aside data and is shown to provide much improved forecasts of daily O₃ concentrations in the eastern United States.

Keywords: Bayesian modeling; Data fusion; Hierarchical model; Markov chain Monte Carlo; Spatial interpolation

Comparison of two estimation methods for surface area concentration using number concentration and mass concentration of combustion-related ultrafine particles by Ji Young Park; Peter C. Raynor; Andrew D. Maynard; Lynn E. Eberly; Gurumurthy Ramachandran (pp. 502-509).

Recent research has suggested that the adverse health effects caused by nanoparticles are associated with their surface area (SA) concentrations. In this study, SA was estimated in two ways using number and mass concentrations and compared with SA (SA_meas) measured using a diffusion charger (DC). Aerosol measurements were made twice: once starting in October 2002 and again starting in December 2002 in Mysore, India in residences that used kerosene or liquefied petroleum gas (LPG) for cooking. Mass, number, and SA concentrations and size distributions by number were measured in each residence. The first estimation method (SA_PSD) used the size distribution by number to estimate SA. The second method (SA_INV) used a simple inversion scheme that incorporated number and mass concentrations while assuming a lognormal size distribution with a known geometrical standard deviation. SA_PSD was, on average, 2.4 times greater (range=1.6–3.4) than SA_meas while SA_INV was, on average, 6.0 times greater (range=4.6–7.7) than SA_meas. The logarithms of SA_PSD and SA_INV were found to be statistically significant predictors of the logarithm of SA_meas. The study showed that particle number and mass concentration measurements can be used to estimate SA with a correction factor that ranges between 2 and 6.

Keywords: Ultrafine particles; Surface area concentration; Estimation methods; Diffusion charger; Number concentration; Mass concentration

Bayesian treatment of a chemical mass balance receptor model with multiplicative error structure by Andrew Keats; Man-Ting Cheng; Eugene Yee; Fue-Sang Lien (pp. 510-519).

The chemical mass balance (CMB) receptor model is commonly used in source apportionment studies as a means for attributing measured airborne particulate matter (PM) to its constituent emission sources. Traditionally, error terms (e.g., measurement and source profile uncertainty) associated with the model have been treated in an additive sense. In this work, however, arguments are made for the assumption of multiplicative errors, and the effects of this assumption are realized in a Bayesian probabilistic formulation which incorporates a ‘modified’ receptor model. One practical, beneficial effect of the multiplicative error assumption is that it automatically precludes the possibility of negative source contributions, without requiring additional constraints on the problem. The present Bayesian treatment further differs from traditional approaches in that the source profiles are inferred alongside the source contributions. Existing knowledge regarding the source profiles is incorporated as prior information to be updated through the Bayesian inferential scheme. Hundreds of parameters are therefore present in the expression for the joint probability of the source contributions and profiles (the posterior probability density function, or PDF), whose domain is explored efficiently using the Hamiltonian Markov chain Monte Carlo method. The overall methodology is evaluated and results compared to the US Environmental Protection Agency's standard CMB model using a test case based on PM data from Fresno, California.

Keywords: Receptor model; Chemical mass balance; Bayesian inference; Multiplicative error; Source apportionment; Hamiltonian Markov chain Monte Carlo

Wind tunnel simulation of environmental controls on fugitive dust emissions from mine tailings by Cheryl McKenna Neuman; J. Wayne Boulton; Steven Sanderson (pp. 520-529).

The development of techniques for determining fugitive dust emissions presents numerous challenges and remains the subject of much investigation. Past approaches have included field based monitoring stations and wind tunnel studies, while more recently, highly portable field units (e.g., PI-SWERL) have been added to our toolkit of instruments and methodologies. In the case of the investigation reported herein, a laboratory wind tunnel study was designed to systematically simulate PM₁₀ emissions from mine tailings for a range of surface treatments. Unique challenges were associated with the project in the sense that the proposed mine and tailings did not exist at the time of the investigation, so that it was impossible to work on-site. Only a small amount of slurry from a milled drill core was available to work with, and there were no established test protocols and few experimental precedents to work from. The slurry formed highly cohesive bricks when dried, similar to crusted playas investigated in field experiments. The PM₁₀ emissions demonstrated strong temporal variation with particle supply limitation. A small amount of vertical dust dispersion was observed, with PM₁₀ concentrations decaying exponentially away from the source. The emission rates obtained are similar in magnitude to those obtained in field analogues. The highly controlled experiment allowed for separation and analysis of several physical controls on PM₁₀ emissions from tailings; namely, the study addressed the degree of disturbance, shrinkage and cracking, and the effects of spigotting, particle settling and re-wetting.

Keywords: Fugitive dust; Emission rates; Wind tunnel; Mine tailings

Impact of mineral components and selected trace metals on ambient PM10 concentrations by Andreas Limbeck; Markus Handler; Christoph Puls; Johannes Zbiral; Heidi Bauer; Hans Puxbaum (pp. 530-538).

PM10 levels of the mineral components Si, Al, Fe, Ca, Mg and some trace metals were measured at three different sites in the urban area of Vienna (Austria). Observed trace metal concentrations varied between less than 0.1ngm⁻³ (Cd) and approximately 200ngm⁻³ (Zn), mineral components showed enhanced concentrations ranging from 0.01μgm⁻³ (Ca) to 16.3μgm⁻³ (Si). The contribution of the respective mineral oxides to PM10 mass concentrations accounted on average for 26.4±16% (n=1090) of the PM10 mass, with enhanced rates in spring and autumn (monthly averages of up to 40%) and decreased contributions in the cold season (monthly averages below 10%). The atmospheric occurrence of Al, Ti and Sr could be assigned to crustal sources, whereas for the elements Ba, Ca, Fe, Mg, Mn and V an increased contribution of non-crustal origin was observed. PM10 levels of As, Cd, Co, Cr, Cu, Ni, Pb, Sb, Sn and Zn were predominantly derived from man-made emissions. Intersite comparison indicated that urban PM10 mass concentrations and PM10 levels of As, Pb and Zn were predominantly influenced from the transport of aerosols from outside into the city, whereas for the elements Ba, Mg, Ca, Cu and Fe a distinctly increased impact of local emissions was observed. The contribution of these urban emissions to total PM10 concentrations was estimated by calculating the so-called “urban impact”, which was found to be 32.7±18% (n=392) in the case of PM10 mass concentrations. The investigated elements accounted on average for 31.3±19% (n=392) of the observed PM10 mass increase. The mean values for the “urban impacts” of individual elements varied between 25.5% (As) and 77.0% (Ba).

Keywords: PM10; Elemental composition; Seasonal variation; Crustal and non-crustal origin; Urban impact; Vienna (Austria)

Gas- and particle-phase distribution of polycyclic aromatic hydrocarbons in two-stroke, 50-cm³ moped emissions by Pasquale Spezzano; Paolo Picini; Dario Cataldi (pp. 539-545).

Gas- and particle-phase polycyclic aromatic hydrocarbons (PAHs) concentrations evaluated in the exhaust of 10 two-stroke, 50-cm³ mopeds belonging to three different levels of emission legislation (EURO-0, EURO-1 and EURO-2) were used to assess the prevalent mechanism driving the gas/particle partitioning of PAHs in moped exhaust. Sampling was performed on a dynamometer bench both during the “cold-start” and the “hot” phases of the ECE-47 driving cycle. Gas and particulate phase PAHs were collected on polyurethane foam (PUF) plugs and 47-mm Pallflex T60A20 filters, respectively, under isokinetic conditions by using sampling probes inserted into the dilution tunnel of a Constant Volume Sampling – Critical Flow Venturi (CVS–CFV) system.The results show that semi-volatile PAHs were predominantly partitioned to the particle phase. The soluble organic fraction (SOF) of the collected particulates ranged between 72 and 98%. Measured total suspended particulate matter normalized partition coefficients ( K_p) were predicted within a factor of 3–5 by assuming absorption into the organic fraction according to a model developed by Harner and Bidleman [Harner, T., Bidleman, T.F., 1998. Octanol–air partition coefficient for describing particle/gas partitioning of aromatic compounds in urban air. Environmental Science & Technology 32, 1494–1502.]. This suggests that the gas/particle partitioning in moped exhaust is mainly driven by the high fraction of organic matter of the emitted particles and that absorption could be the main partitioning mechanism of PAHs.

Keywords: Exhaust emission; Gas/particle distribution; Moped; Particulate matter; PAHs; SOF

Roadside nanoparticles corresponding to vehicle emissions during one signal cycle by Hiroaki Minoura; Hideto Takekawa; Shigeo Terada (pp. 546-556).

The behavior of nanoparticles (NPs) in the roadside atmosphere has not been clarified because it involves unstable volatile components. It was thought that the number concentration (NC) and NP size distribution change due to variations in traffic conditions (e.g., traffic volume [TV], velocity, acceleration, etc.) near the intersection, but the SMPS (Scanning Mobility Particle Sizer) lacks the temporal resolution required for rapid, transient measurements. Using a fast-response aerosol spectrometer capable of providing near-instantaneous particle NC measurements in real time, the behavior of NPs during one signal cycle became clear, and it was understood that the effect of condensation/evaporation processes is important, in addition to coagulation. As for the relation of the NC in proportion to the TV, this did not show a constant line but rather a hysteresis curve during the signal cycle, because the gas-particle equilibrium state at the roadside atmosphere was variable. Using two points of simultaneous measurement and on-board measurement, the behavior of NPs could be confirmed in response to the characteristics of automotive exhaust, which varied due to the on-road driving state, engine conditions, vehicle position, or traffic light timing, at the intersection. The on-board measurement of NP size distribution in the exhaust plume from a diesel vehicle was carried out as a reference for direct particle emissions, compared with the roadside NPs. The coagulation/deposition model simulation using the direct particle emissions underestimated the NCs compared with the observed values. The gas-particle equilibrium model could explain the underestimated portion caused by the condensation of ambient VOC (Volatile Organic Compounds) onto the particles. If this hypothesis is correct, the condensable VOC amount in the roadside atmosphere is suggested to be very large.

Keywords: Nanoparticle; Number concentration; Volatile component; Traffic; Diesel; Instrumented junction

Variation of dust layer height in the northern Taklimakan Desert in April 2002 by Heon-Sook Kim; Yuichi Nagata; Kenji Kai (pp. 557-567).

LIDAR observations were conducted in the northern Taklimakan Desert to investigate the vertical distribution of dust in April 2002. During the observation period, a dust outbreak occurred on 13 April, remaining over the desert for several days. Despite only slight variations being observed in dust layer height before the dust event, marked diurnal variation in dust layer height was observed after the dust event. In this study, we conducted two numerical simulations to investigate differences in the variation exhibited by the dust layer heights before and after the dust event, and assessed the influence of meteorological conditions on this variation. The simulated results show that the clearly diurnal variation in dust layer height is strongly influenced by local circulation which is affected by the characteristic topography and synoptic conditions of the Tarim Basin.

Keywords: LIDAR observation; Dust layer height; Numerical simulation; Floating dust; Taklimakan Desert

Suppression of precipitation by dust particles originated in the Tibetan Plateau by Yongxiang Han; Xiaomin Fang; Tianliang Zhao; Huzhi Bai; Shichang Kang; Lianchun Song (pp. 568-574).

Dust aerosols play an important role in modulating the hydrologic cycle. The Tibetan Plateau (TP) is little polluted by human activities as an ideal site to study the effect of dust aerosol on precipitation. In this study, observational data of dust storms and precipitation in the TP and its vicinities as well as CALIPSO satellite data were used to analyze the distributions and vertical structure of dust storms on the plateau. The results showed that dust storms occur with high frequency and raise dust particles into the troposphere from ground level to a height of 5–9 km to modulate the hydrologic cycle in the TP. There are significant negative correlations between dust aerosol and precipitation in the dust source regions during the period of both 40 and 200 years. It is found that the role of precipitation in suppressing dust storms could be unimportant, while dust aerosol may play an important role in suppressing precipitation in the hinterland of the TP. Our study provides a potential approach to better understand the climate changes in the TP.

Keywords: Tibetan Plateau; Dust aerosol; Precipitation; CALIPSO

New approach using lidar measurements to characterize spatiotemporal aerosol mass distribution in an underground railway station in Paris by J.-C. Raut; P. Chazette; A. Fortain (pp. 575-583).

For the first time eye safe lidar measurements were performed at 355 nm simultaneously to in situ measurements in an underground station so as to test the potential interest of active remote sensing measurements to follow the spatiotemporal evolution of aerosol content inside such a confined microenvironment. The purpose of this paper is to describe different methods enabling the conversion of lidar-derived aerosol extinction coefficient into aerosol mass concentrations (PM_2.5 and PM₁₀). A theoretical method based on a well marked linear regression between mass concentrations simulated from the size distribution and extinction coefficients retrieved from Mie calculations provides averaged mass to optics' relations over the campaign for traffic (6.47 × 10⁵ μg m⁻²) or no traffic conditions (3.73 × 10⁵ μg m⁻²). Two empirical methods enable to significantly reduce CPU time. The first one is based upon the knowledge of size distribution measurements and scattering coefficients from nephelometer and allows retrieving mass to optics' relations for well determined periods or particular traffic conditions, like week-ends, with a good accuracy. The second method, that is more direct, is simply based on the ratio between TEOM concentrations and extinction coefficients obtained from nephelometer. This method is easy to set up but is not suitable for nocturnal measurements where PM stabilization time is short. Lidar signals thus converted into PM concentrations from those approaches with a fine accuracy (30%) provide a spatiotemporal distribution of concentrations in the station. This highlights aerosol accumulation in one side of the station, which can be explained by air displacement from the tunnel entrance. Those results allow expecting a more general use of lidar measurement to survey indoor air quality.

Keywords: Subway; PM; _2.5; PM; ₁₀; Mass spatial distribution; Lidar; Underground station

Aircraft measurements of O₃, NO _x, CO, VOCs, and SO₂ in the Yangtze River Delta region by Fuhai Geng; Qiang Zhang; Xuexi Tie; Mengyu Huang; Xincheng Ma; Zhaoze Deng; Qiong Yu; Jiannong Quan; Chunsheng Zhao (pp. 584-593).

In this study, air pollutants, including ozone (O₃), nitrogen oxides (NO _x=NO+NO₂), carbon monoxides (CO), sulfur dioxide (SO₂), and volatile organic compounds (VOCs) measured in the Yangtze River Delta (YRD) region during several air flights between September/30 and October/11 are analyzed. This measurement provides horizontal and vertical distributions of air pollutants in the YRD region. The analysis of the result shows that the measured O₃ concentrations range from 20 to 60ppbv. These values are generally below the US national standard (84ppbv), suggesting that at the present, the O₃ pollutions are modest in this region. The NO _x concentrations have strong spatial and temporal variations, ranging from 3 to 40ppbv. The SO₂ concentrations also have large spatial and temporal variations, ranging from 1 to 35ppbv. The high concentrations of CO are measured with small variations, ranging from 3 to 7ppmv. The concentrations of VOCs are relatively low, with the total VOC concentrations of less than 6ppbv. The relative small VOC concentrations and the relative large NO _x concentrations suggest that the O₃ chemical formation is under a strong VOC-limited regime in the YRD region. The measured O₃ and NO _x concentrations are strongly anti-correlated, indicating that enhancement in NO _x concentrations leads to decrease in O₃ concentrations. Moreover, the O₃ concentrations are more sensitive to NO _x concentrations in the rural region than in the city region. The ratios of Δ[O₃]/Δ[NO _x] are −2.3 and −0.25 in the rural and in the city region, respectively. In addition, the measured NO _x and SO₂ concentrations are strongly correlated, highlighting that the NO _x and SO₂ are probably originated from same emission sources. Because SO₂ emissions are significantly originated from coal burnings, the strong correlation between SO₂ and NO _x concentrations suggests that the NO _x emission sources are mostly from coal burned sources. As a result, the future automobile increases could lead to rapid enhancements in O₃ concentrations in the YRD region.

Keywords: Air pollutants in the YRD region; Aircraft measurements

Synoptic evaluation of regional PM2.5 concentrations by Kenneth J. Walsh; Matthew Milligan; John Sherwell (pp. 594-603).

By comparing short-term fluctuations in PM2.5 species concentrations among nearby air quality monitors and among species, it becomes possible to understand the regional and local events leading to higher concentrations. This approach was applied at thirteen sites in the Maryland area for the 2001–2006 timeframe in order to identify and explain the behavior of eighteen different analytes as well as the daily Air Quality Index.Findings included identification of local upwind events such as fireworks displays, construction and demolition, the spatial extent of sulfate, nitrate, and ammonium correlations between ground-level monitors, correlations between some crustal species to indicate similar emissions sources in urban areas, and indicators of particle adsorption as a rate-limiting step for certain species. For example, the bromine behavior suggests that bromine concentrations on particulate matter may be limited by the particle adsorption rate and thus show a dependence on the Air Quality Index measurements.

Keywords: Particulate matter; Speciation; Air Quality Index; Spatial trends; Synoptic perturbation; Bromine

The global impact of ozone on agricultural crop yields under current and future air quality legislation by Rita Van Dingenen; Frank J. Dentener; Frank Raes; Maarten C. Krol; Lisa Emberson; Janusz Cofala (pp. 604-618).

In this paper we evaluate the global impact of surface ozone on four types of agricultural crop. The study is based on modelled global hourly ozone fields for the year 2000 and 2030, using the global 1°×1° 2-way nested atmospheric chemical transport model (TM5). Projections for the year 2030 are based on the relatively optimistic “current legislation (CLE) scenario”, i.e. assuming that currently approved air quality legislation will be fully implemented by the year 2030, without a further development of new abatement policies. For both runs, the relative yield loss due to ozone damage is evaluated based on two different indices (accumulated concentration above a 40ppbV threshold and seasonal mean daytime ozone concentration respectively) on a global, regional and national scale. The cumulative metric appears to be far less robust than the seasonal mean, while the seasonal mean shows satisfactory agreement with measurements in Europe, the US, China and Southern India and South-East Asia.Present day global relative yield losses are estimated to range between 7% and 12% for wheat, between 6% and 16% for soybean, between 3% and 4% for rice, and between 3% and 5% for maize (range resulting from different metrics used). Taking into account possible biases in our assessment, introduced through the global application of “western” crop exposure–response functions, and through model performance in reproducing ozone-exposure metrics, our estimates may be considered as being conservative.Under the 2030 CLE scenario, the global situation is expected to deteriorate mainly for wheat (additional 2–6% loss globally) and rice (additional 1–2% loss globally). India, for which no mitigation measures have been assumed by 2030, accounts for 50% of these global increase in crop yield loss. On a regional-scale, significant reductions in crop losses by CLE-2030 are only predicted in Europe (soybean) and China (wheat).Translating these assumed yield losses into total global economic damage for the four crops considered, using world market prices for the year 2000, we estimate an economic loss in the range $14–$26 billion. About 40% of this damage is occurring in China and India. Considering the recent upward trends in food prices, the ozone-induced damage to crops is expected to offset a significant portion of the GDP growth rate, especially in countries with an economy based on agricultural production.

Keywords: Ozone; Crop damage; Global; Model; Impact assessment

Relationship between leaf antioxidants and ozone injury in Nicotiana tabacum ‘Bel-W3’ under environmental conditions in São Paulo, SE – Brazil by Marisia P. Esposito; Mauricio L. Ferreira; Silvia M.R. Sant'Anna; Marisa Domingos; Silvia R. Souza (pp. 619-623).

Previous studies have reported that the extent of leaf injury in Nicotiana tabacum “Bel-W3” exposed to environmental conditions in the city of São Paulo is influenced by weather conditions. This influence may occur by means of antioxidant responses. Thus, this study aimed to evaluate whether daily antioxidant responses to environmental variations interfere on the progression of leaf injury on plants of this cultivar during their exposure in a state park of São Paulo and to determine a linear combination of variables, among antioxidants and environmental factors, which mostly explain this visible response. Plants were exposed at the mentioned site for 14days in four different experiments. During each experiment, three plants were daily sampled to determine the accumulated percentage of leaf area affected by necrosis and antioxidant responses (concentrations of total ascorbic acid (AA) and activity of superoxide dismutase (SOD) and peroxidases (POD)). Ozone concentrations and weather conditions were also daily measured. Pearson correlations and multivariate analyses assessed the relationship between biological and environmental variables. Leaf injury appeared between the 3rd and 6thdays of exposure and increased over the exposure periods. The daily concentrations of AA tended to decrease with time of exposure in all experiments, but the activity of SOD and POD oscillated during plant exposure. Positive correlations were observed between AA or SOD and O₃ concentrations, as well as negative correlations between AA and air temperature. The increasing percentage of leaf necrosis across the whole period was explained by decreasing levels of AA 2days before injury estimation and by higher O₃ concentrations 5days before ( R²=0.36; p<0.001). The use of N. tabacum Bel-W3 as a bioindicator can be restricted by leaf antioxidant responses to both atmospheric contamination and weather conditions.

Keywords: Nicotiana tabacum; “Bel-W3”; Antioxidants; Leaf injury; Ozone

Mobile measurements of aerosol number and volume size distributions in an Alpine valley: Influence of traffic versus wood burning by S. Weimer; C. Mohr; R. Richter; J. Keller; M. Mohr; A.S.H. Prévôt; U. Baltensperger (pp. 624-630).

The spatial variability of highly time resolved size distributions was investigated in a narrow valley which provides the opportunity to study the impact of different sources on ambient particle concentrations during summer and winter time. The measurements were performed with a Fast Mobility Particle Sizer (FMPS) from TSI, Inc. on a mobile laboratory in Southern Switzerland. The results indicate enhanced number concentrations (between 150 000 and 500 000 cm⁻³) along the busy highway A2 which is the main transit route through the Swiss Alps connecting the northern and southern part of Switzerland. Especially the nanoparticles with diameters lower than 30 nm showed strongly increased number concentrations on the highway both in summer and winter. In winter time, high aerosol volume concentrations (PM_0.3) were found in villages where wood burning is often used for heating purposes. Both traffic and wood burning were found to be important sources for particulate mass which accumulates during temperature inversions in winter time. Traffic was the dominant and wood burning a minor source for the nanoparticle number concentration. This is important regarding health impacts and its attribution to different sources because wood burning might contribute most to particulate mass whereas at the same time and place traffic contributes most to particulate number. In addition, during summer time volatility measurements were performed with the FMPS showing that the nucleation mode prevalently seen on the highway was removed by more than 95% by thermal treatment.

Keywords: FMPS; Nucleation mode; Mobile measurements; Wood burning; Traffic

Characterisation of PM₁₀ atmospheric aerosols for the wet season 2005 at two sites in East Africa by Stelyus L. Mkoma; Willy Maenhaut; Xuguang Chi; Wan Wang; Nico Raes (pp. 631-639).

Ambient daily PM₁₀ aerosol samples were collected at two sites in Tanzania in May and June 2005 (during the wet season), and their chemical characteristics were studied. The sites were a rural site in Morogoro and an urban kerbside site in Dar es Salaam. A Gent PM₁₀ stacked filter unit sampler with sequential Nuclepore polycarbonate filters, providing fine and coarse size fractions, and a PM₁₀ sampler with quartz fibre filters were deployed. Parallel collections of 24h were made with the two samplers and the number of these collections was 13 in Morogoro and 16 in Dar es Salaam. The average mass concentration of PM₁₀ was 27±11μg/m³ in Morogoro and 51±21μg/m³ in Dar es Salaam. In Morogoro, the mean concentrations of organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC) were 6.8, 0.51, and 2.8μg/m³, respectively. In contrast, higher mean concentrations (11.9, 4.6, and 3.3μg/m³, respectively) were obtained for Dar es Salaam. At both sites, species and elements, such as black carbon, NH₄⁺, non-sea-salt SO₄²⁻, K, and Ni (and at Dar es Salaam also V, As, Br, and Pb) were mainly present in the fine size fraction. The common crustal and sea-salt elements, including Na, Mg, Al, Si, Cl, Ca, Ti, Mn, Fe, and Sr, and also NO₃⁻ and P (and to a lesser extent Cu and Zn) were concentrated in the coarse particles. Aerosol chemical mass closure indicated that the PM₁₀ mass in Morogoro consisted, on average, of 48% organic matter (OM), 44% crustal matter, 4% sea salt, and 2% EC, while in Dar es Salaam OM, crustal matter, sea salt, and EC represented 37%, 32%, 9%, and 9% of the PM₁₀ mass. The contributions of the secondary inorganic aerosol (non-sea-salt sulphate, nitrate, and ammonium) were small, i.e., only 5% in total at each site. Carbonaceous materials and crustal matter were thus the most important components of the PM₁₀ mass. It is suggested that biomass burning is a major contributor to the OM; at Dar es Salaam there is also a very substantial contribution from traffic. A source apportionment calculation indicated that 68% of the OC at this site originated from traffic exhaust versus 32% from charcoal burning. The crustal matter at Morogoro is likely mainly attributable to soil dust resuspension, whereas in Dar es Salaam it is likely mostly resuspended road dust.

Keywords: PM; ₁₀; aerosols; Carbonaceous species; Elements; Water-soluble ions; Aerosol chemical mass closure; Tanzania

Assessment of heavy metal releases from the use phase of road transport in Europe by Ulrike Kummer; Jozef Pacyna; Elisabeth Pacyna; Rainer Friedrich (pp. 640-647).

An emission inventory was compiled for heavy metal air emissions from road transport in Europe (EU-40). For the database, country-specific data was taken such as the diesel and gasoline fuel consumption per country, the content of Pb in gasoline and diesel fuel and the share of different vehicle types. For tyre and brake wear emissions, average wear rates and heavy metal contents of different materials were used to develop emission factors for tyre and brake wear. It covers exhaust emissions (Pb from gasoline and diesel) as well as non-exhaust emissions (As, Cd, Cr, Ni and Pb from the wear of brake linings and vehicle tyres). The base year is 2000, and two scenarios were developed for 2010, a business as usual (BAU) scenario and a maximum feasible technical reduction (MFTR) scenario. Both result in a remarkable decrease in Pb exhaust emissions and a rising share of non-exhaust emissions. To assess the results, the inventory is (a) compared to an inventory compiled with a top-down approach that covers the same area and years but only emissions from combustion processes and (b) added to an inventory covering all sectors for heavy metal air emissions.

Keywords: Road transport; Heavy metals; Emission inventory; Brake wear; Tyre wear

Emission of polycyclic aromatic hydrocarbons from gasohol and ethanol vehicles by Rui de Abrantes; João Vicente de Assunção; Célia Regina Pesquero; Roy Edward Bruns; Raimundo Paiva Nóbrega (pp. 648-654).

The exhaust emission of the polycyclic aromatic hydrocarbons (PAHs) considered toxic to human health were investigated on two spark ignition light duty vehicles, one being gasohol (Gasohol, in Brazil, is the generic denomination for mixtures of pure gasoline plus 20–25% of anhydrous ethyl alcohol fuel (AEAF).)-fuelled and the other a flexible-fuel vehicle fuelled with hydrated ethanol. The influence of fuel type and quality, aged lubricant oil type and use of fuel additives on the formation of these compounds was tested using standardized tests identical to US FTP-75 cycle. PAH sampling and chemical analysis followed the basic recommendations of method TO-13 (United States. Environmental Protection Agency, 1999. Compendium Method TO-13A – Determination of polycyclic Aromatic hydrocarbons (PAH) in Ambient Air Using Gas Chromatography/Mass Spectrometry (CG/MS). Center for environmental research information, Cincinnati, p. 78), with the necessary modification for this particular application.Results showed that the total PAH emission factor varied from 41.9μgkm⁻¹ to 612μgkm⁻¹ in the gasohol vehicle, and from 11.7μgkm⁻¹ to 27.4μgkm⁻¹ in the ethanol-fuelled vehicle, a significant difference in favor of the ethanol vehicle. Generally, emission of light molecular weight PAHs was predominant, while high molecular weights PAHs were not detected. In terms of benzo( a)pyrene toxicity equivalence, emission factors varied from 0.00984μgTEQkm⁻¹ to 4.61μgTEQkm⁻¹ for the gasohol vehicle and from 0.0117μgTEQkm⁻¹ to 0.0218μgTEQkm⁻¹ in the ethanol vehicle.For the gasohol vehicle, results showed that the use of fuel additive causes a significant increase in the emission of naphthalene and phenanthrene at a confidence level of 90% or higher; the use of rubber solvent on gasohol showed a reduction in the emission of naphthalene and phenanthrene at the same confidence level; the use of synthetic oil instead of mineral oil also contributed significantly to a decrease in the emission of naphthalene and fluorene. In relation to the ethanol vehicle, the same factors were tested and showed no statistically significant influence on PAH emission.

Keywords: Vehicular emission; PAH; Air pollution; Toxic pollutants; Gasohol; Ethanol

Determination of PAHs in diesel particulate matter using thermal extraction and solid phase micro-extraction by R. Ballesteros; J.J. Hernández; L.L. Lyons (pp. 655-662).

Determination of polycyclic aromatic hydrocarbons (PAHs) from chemical analysis of the diesel particulate matter (DPM) requires considerable sampling expertise and is often time-consuming because sample preparation demands strict extraction procedures due to the complex nature of the DPM matrix. In this study, a method to measure the emissions of the 16-U.S. Environmental Protection Agency (EPA) priority PAHs adsorbed in diesel particles has been developed. This method involves the capture of the DPM in glass microfibre filters, thermal extraction of the compounds from the particulate matrix in a thermogravimetric analyzer (TGA), determination of the concentration by means of a solid phase micro-extraction (SPME) fibre and subsequent analysis using a gas chromatograph coupled to a mass spectrometer (GC/MS). Analyses of a fully characterised DPM prepared by the National Institute of Standards and Technology, NIST (SRM 1650b), were performed and calculated errors showed that the method is capable of giving reliable quantitative data. Additionally, DPM collected from a diesel engine was analyzed and the results showed the high method sensitivity to the engine operating conditions.

Keywords: Thermogravimetric analysis; Solid phase micro-extraction; GC–MS; Diesel particulate matter; PAHs

Sensitivity analysis of an ozone deposition model by R. Mészáros; I. Gy. Zsély; D. Szinyei; Cs. Vincze; I. Lagzi (pp. 663-672).

In this study, sophisticated sensitivity analyses of a detailed ozone dry deposition model were performed for five soil types (sand, sandy loam, loam, clay loam, clay) and four land use categories (agricultural land, grass, coniferous and deciduous forests). Deposition velocity and ozone flux depend on the weather situation, physiological state of the plants and numerous surface-, vegetation-, and soil-dependent parameters. The input data and the parameters of deposition-related calculations all have higher or lower spatial and temporal variability. We have investigated the effect of the variability of the meteorological data (cloudiness, relative humidity and air temperature), plant-dependent (leaf area index and maximum stomatal conductance) and soil-dependent (soil moisture) parameters on ozone deposition velocity. To evaluate this effect, two global methods, the Morris method and the Monte Carlo analysis with Latin hypercube sampling were applied. Additionally, local sensitivity analyses were performed to estimate the contribution of non-stomatal resistances to deposition velocity. Using the Monte Carlo simulations, the ensemble effect of several nonlinear processes can be recognised and described. Based on the results of the Morris method, the individual effects on deposition velocity are found to be significant in the case of soil moisture and maximum stomatal conductance. Temperature and leaf area index are also important factors; the former is primarily in the case of agricultural land, while the latter is for grass and coniferous forest. The results of local sensitivity analyses reveal the importance of non-stomatal resistances.

Keywords: Ozone fluxes; Deposition model; Sensitivity analyses; Monte Carlo method; Morris method

CFD modelling of small particle dispersion: The influence of the turbulence kinetic energy in the atmospheric boundary layer by C. Gorlé; J. van Beeck; P. Rambaud; G. Van Tendeloo (pp. 673-681).

When considering the modelling of small particle dispersion in the lower part of the Atmospheric Boundary Layer (ABL) using Reynolds Averaged Navier Stokes simulations, the particle paths depend on the velocity profile and on the turbulence kinetic energy, from which the fluctuating velocity components are derived to predict turbulent dispersion. It is therefore important to correctly reproduce the ABL, both for the velocity profile and the turbulence kinetic energy profile.For RANS simulations with the standard k– ε model, Richards and Hoxey (1993. Appropriate boundary conditions for computational wind engineering models using the k–ε turbulence model. Journal of Wind Engineering and Industrial Aerodynamics 46–47, 145–153.) proposed a set of boundary conditions which result in horizontally homogeneous profiles. The drawback of this method is that it assumes a constant profile of turbulence kinetic energy, which is not always consistent with field or wind tunnel measurements. Therefore, a method was developed which allows the modelling of a horizontally homogeneous turbulence kinetic energy profile that is varying with height.By comparing simulations performed with the proposed method to simulations performed with the boundary conditions described by Richards and Hoxey (1993. Appropriate boundary conditions for computational wind engineering models using the k–ε turbulence model. Journal of Wind Engineering and Industrial Aerodynamics 46–47, 145–153.), the influence of the turbulence kinetic energy on the dispersion of small particles over flat terrain is quantified.

Keywords: Computational Fluid Dynamics (CFD); Numerical simulation; Atmospheric Boundary Layer (ABL); Turbulence kinetic energy; Particle dispersion

Comparative assessment of air quality in two health resorts using carbon isotopes and palynological analyses by M. Górka; M.O. Jędrysek; J. Maj; A. Worobiec; A. Buczyńska; E. Stefaniak; A. Krata; R. Van Grieken; A. Zwoździak; I. Sówka; J. Zwoździak; D. Lewicka-Szczebak (pp. 682-688).

This paper describes results of applying the palynological and carbon isotopic analysis of the organic fraction of Total Suspended Particles (TSP) to discriminate distinct pollution sources and assess the anthropogenic impact for the investigated areas. The samples of atmospheric particles were collected in Czerniawa and Cieplice (two health resorts in Lower Silesia, SW Poland) twice a year in summer and winter season (from July 2006 to February 2008). The palynological spectra represent in the vast majority local plant communities without a noticeable contribution of long-transported plant particles. Palynological analysis revealed also differences in the specificity of the two sampling areas, i.e. the higher contribution of identified organic material in Czerniawa stands for more natural character of this site, but is also responsible for the higher allergic pressure when compared to Cieplice. The carbon isotopic composition of TSP varied seasonally ( δ¹³C value from −27.09‰ in summer to −25.47‰ in winter). The increased δ¹³C value in winter (heating period) is most probably caused by uncontrolled contribution of coal soot. On the basis of isotopic mass balance the calculated contribution of anthropogenic organic particles in the atmosphere reached in winter season 72% in Czerniawa and 79% in Cieplice.

Keywords: Lower Silesia; Poland; TSP; Carbon stable isotopes; Palynology; Palynomorphs

Particulate matter at a rural location in southern England during 2006: Model sensitivities to precursor emissions by Richard Derwent; Claire Witham; Alison Redington; Michael Jenkin; John Stedman; Rachel Yardley; Garry Hayman (pp. 689-696).

A moving air parcel trajectory model has been used to estimate the mid-afternoon mass concentrations of a number of suspended particulate matter (PM) components for each day of 2006 for a rural location, Harwell, Oxfordshire, in the southern UK. A large number of equally probable and randomly selected 96-h 3-dimensional air mass trajectories were used to describe the variability of the atmospheric transport paths during each day. A chemical kinetic description was given for the major PM formation processes. The linearity of the chemical production pathways forming the secondary PM components was examined by sensitivity studies to 30% reductions in SO₂, NO _x, NH₃, VOC and CO emissions. The chemical environment revealed by these sensitivity studies appeared to be ‘ammonia-limited’. Consequently, PM mass concentrations appeared to be markedly non-linear with PM precursor emissions. Policy strategies for PM_2.5 therefore need to take into account emission reductions for a wide range of primary PM components and secondary PM precursors and to focus primarily on the abatement of NH₃. This complex interlinking may help to explain why PM levels have remained constant despite falling primary PM emissions.

Keywords: PM; _2.5; mass concentrations; PM nitrate; PM sulphate; PM ammonium; Emission sensitivities

Characterization of on-road vehicle emission factors and microenvironmental air quality in Beijing, China by Dane Westerdahl; Xing Wang; Xiaochuan Pan; K. Max Zhang (pp. 697-705).

In this paper, we report the results and analysis of a recent field campaign in August 2007 investigating the impacts of emissions from transportation on air quality and community concentrations in Beijing, China. We conducted measurements in three different environments, on-road, roadside and ambient. The carbon monoxide, black carbon and ultrafine particle number emission factors for on-road light-duty vehicles are derived to be 95gkg⁻¹-fuel, 0.3gkg⁻¹-fuel and 1.8×10¹⁵ particleskg⁻¹-fuel, respectively. The emission factors for on-road heavy-duty vehicles are 50gkg⁻¹-fuel, 1.3gkg⁻¹-fuel and 1.1×10¹⁶ particleskg⁻¹-fuel, respectively. The carbon monoxide emission factors from this study agree with those derived from remote sensing and on-board vehicle emission testing systems in China. The on-road black carbon and particle number emission factors for Chinese vehicles are reported for the first time in the literature. Strong traffic impacts can be observed from the concentrations measured in these different environments. Most clear is a reflection of diesel truck traffic activity in black carbon concentrations. The comparison of the particle size distributions measured at the three environments suggests that the traffic is a major source of ultrafine particles. A four-day traffic control experiment conducted by the Beijing Government as a pilot to test the effectiveness of proposed controls was found to be effective in reducing extreme concentrations that occurred at both on-road and ambient environments.

Keywords: Olympics; Air pollution; PM; Aerosols; Soot; Elemental carbon; Climate change

Effect of interior door position on room-to-room differences in residential pollutant concentrations after short-term releases by Andrea R. Ferro; Neil E. Klepeis; Wayne R. Ott; William W. Nazaroff; Lynn M. Hildemann; Paul Switzer (pp. 706-714).

Residential interior door positions influence the pollutant concentrations that result from short-term indoor sources, such as cigarettes, candles, and incense. To elucidate this influence, we reviewed past studies and conducted new experiments in three residences: a single-story 714m³ ranch-style house, a 510m³ two-story split-level house, and a 200m³ two-story house. During the experiments, we released sulfur hexafluoride or carbon monoxide tracer gas over short periods (≤30min) and measured concentrations in the source room and at least one other (receptor) room for various interior door opening positions. We found that closing a door between rooms effectively prevented transport of air pollutants, reducing the average concentration in the receptor room relative to the source room by 57–100% over exposure periods of 1–8h. When intervening doors were partially or fully open, the reduction in average concentrations ranged from 3% to 99%, varying as a function of door opening width and the distance between source and receptor rooms.

Keywords: Environmental tobacco smoke; Secondhand smoke; Combustion sources; Indoor air quality; Exposure; Interzonal flow

Sequencing diurnal air flow patterns for ozone exposure assessment around Houston, Texas by Swathi Pakalapati; Scott Beaver; Jose A. Romagnoli; Ahmet Palazoglu (pp. 715-723).

Understanding the human health impacts of ground level ozone requires detailed knowledge of its spatial–temporal distribution beyond that provided by surface monitoring networks. Here, a novel methodology based on unsupervised multivariate statistical techniques has been developed and used to identify the transport and dispersion patterns of tropospheric ozone. The hierarchical clustering method is used to visualize air flow patterns at two time scales relevant for ozone buildup. Sequentially executed statistical methods consider hourly 1-h surface wind field measurements. First, clustering is performed at the hourly time scale to identify 1-h surface flow patterns. Then, sequencing is performed at the daily time scale to identify groups of days sharing similar diurnal cycles for the surface flow. Selection of appropriate numbers of air flow patterns allows inference of regional transport and dispersion patterns for understanding population exposure to ozone. The methods are applied to the Houston, Galveston, and Beaumont-Port Arthur, TX study domain. Representative hourly wind field patterns are determined for the entire 2004 ozone season. Then, sequencing is performed for the 32 days in exceedance of the NAAQS for 8-h ozone. Four diurnal flow patterns capturing different ozone exceedance scenarios are isolated; each scenario is associated with a distinct spatial distribution for atmospheric pollutants.

Keywords: Air quality; Wind field analysis; k; -means clustering; Sea breeze; Ozone exposure assessment

Vegetation exposure to ozone over the continental United States: Assessment of exposure indices by the Eta-CMAQ air quality forecast model by Daniel Q. Tong; Rohit Mathur; Daiwen Kang; Shaocai Yu; Kenneth L. Schere; George Pouliot (pp. 724-733).

The main use of air quality forecast (AQF) models is to predict ozone (O₃) exceedances of the primary O₃ standard for informing the public of potential health concerns. This study presents the first evaluation of the performance of the Eta-CMAQ air quality forecast model to predict a variety of widely used seasonal mean and cumulative O₃ exposure indices associated with vegetation using the U.S. AIRNow O₃ observations. These exposure indices include two concentration-based O₃ indices, M7 and M12 (the seasonal means of daytime 7-h and 12-h O₃ concentrations, respectively), and three cumulative exposure-based indices, SUM06 (the sum of all hourly O₃ concentrations≥0.06ppm), W126 (hourly concentrations weighed by a sigmoidal weighting function), and AOT40 (O₃ concentrations accumulated over a threshold of 40ppb during daylight hours). During a three-month simulation (July–September 2005), the model over predicted the M7 and M12 values by 8–9ppb, or a NMB value of 19% and a NME value of 21%. The model predicts a central belt of high O₃ extending from Southern California to Middle Atlantic where the seasonal means, M7 and M12 (the seasonal means of daytime 7-h and 12-h O₃ concentrations), are higher than 50ppbv. In contrast, the model is less capable of reproducing the observed cumulative indices. For AOT40, SUM06 and W126, the NMB and NME values are two- to three-fold of that for M7, M12 or peak 8-h O₃ concentrations. The AOT40 values range from 2 to 33ppmh by the model and from 1 to 40ppmh by the monitors. There is a significantly higher AOT40 value experienced in the United States in comparison to Europe. The domain-wide mean SUM06 value is 14.4ppmh, which is about 30% higher than W126, and 40% higher than AOT40 calculated from the same 3-month hourly O₃ data. This suggests that SUM06 and W126 represent a more stringent standard than AOT40 if either the SUM06 or the W126 was used as a secondary O₃ standard. Although CMAQ considerably over predicts SUM06 and W126 values at the low end, the model under predicts the extreme high exposure values (>50ppmh). Most of these extreme high values are found at inland California sites. Based on our analysis, further improvement of the model is needed to better capture cumulative exposure indices.

Keywords: Vegetation exposure; Ozone (O; ₃; ); CMAQ; Air quality forecast; Crop; Regional air quality; Exposure index; Air quality standard

Influence of wall roughness on the dispersion of a passive scalar in a turbulent boundary layer by P. Salizzoni; R. Van Liefferinge; L. Soulhac; P. Mejean; R.J. Perkins (pp. 734-748).

Many towns and cities consist of similarly sized buildings in relatively regular arrangements with smaller scale roughness elements such as roofs, chimneys and balconies. The objective of this study is to investigate how small scale roughness elements modify the influence of the large scale organized roughness on the dispersion of a passive scalar in a turbulent boundary layer. Wind tunnel experiments were performed using a passive tracer released from a line source and concentration profiles were measured with a Flame Ionisation Detector. The measurements are compared with numerical solutions of the advection–diffusion equation.The results show that decreasing the cavity aspect ratio increases the turbulent vertical mass fluxes, and that the small scale roughness enhances these fluxes, but only in the skimming flow regime. Numerical simulations showed that outside the roughness sub-layer (RSL) the changes in surface roughness could be accounted for by a simple variation of the friction velocity, but inside the RSL the spatial variability of the flow imposed by the roughness elements has much more influence. A simple model for a spatially averaged dispersion coefficient in the RSL has been developed and is shown to agree satisfactorily with the concentrations measured in these experiments.

Keywords: Passive scalar dispersion; Roughness; Urban canopy; Turbulent boundary layer

Ambiguities inherent in sums-of-squares-based error statistics by Cort J. Willmott; Kenji Matsuura; Scott M. Robeson (pp. 749-752).

Commonly used sums-of-squares-based error or deviation statistics—like the standard deviation, the standard error, the coefficient of variation, and the root-mean-square error—often are misleading indicators of average error or variability. Sums-of-squares-based statistics are functions of at least two dissimilar patterns that occur within data. Both the mean of a set of error or deviation magnitudes (the average of their absolute values) and their variability influence the value of a sum-of-squares-based error measure, which confounds clear assessment of its meaning. Interpretation problems arise, according to Paul Mielke, because sums-of-squares-based statistics do not satisfy the triangle inequality. We illustrate the difficulties in interpreting and comparing these statistics using hypothetical data, and recommend the use of alternate statistics that are based on sums of error or deviation magnitudes.

Keywords: Error statistics; Standard deviation; Standard error; Mean-absolute deviation

Measurement of total site mercury emissions from a chlor-alkali plant using ultraviolet differential optical absorption spectroscopy and cell room roof-vent monitoring by Eben D. Thoma; Cary Secrest; Eric S. Hall; Donna Lee Jones; Richard C. Shores; Mark Modrak; Ram Hashmonay; Phil Norwood (pp. 753-757).

This technical note describes a United States Environmental Protection Agency (U.S. EPA) measurement project to determine elemental mercury (Hg⁰) emissions from a mercury cell chlor-alkali (MCCA) facility in the southeastern U.S. during a 53-day monitoring campaign in the fall of 2006. The optical remote sensing (ORS) area source measurement method EPA OTM 10 was used to provide Hg⁰ flux data for the site. These results are reported and compared with cell room roof-vent monitoring data acquired by the facility for similar time periods. The 24-h extrapolated mercury emission rate estimates determined by the two monitoring approaches are shown to be similar with overall averages in the 400gday⁻¹ range with maximum values around 1200gday⁻¹. Results from the OTM 10 measurements, which include both cell room emissions and potential fugitive sources outside the cell room, are shown to be approximately 10% higher than cell room monitoring results indicating that fugitive emissions from outside the cell room produce a small but measurable effect for this site.

Keywords: Mercury; Chlor-alkali; Fugitive emissions; UV-DOAS; Open path; EPA OTM 10

Sections

Personal tools

Atmospheric Environment (v.43, #3)

Sections

Personal tools

Local resources

Atmospheric Environment (v.43, #3)