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Atmospheric Environment (v.41, #26)

Editorial board (pp. i).

Modelling and assessing trends in traffic-related emissions using a generalised additive modelling approach by David C. Carslaw; Sean D. Beevers; James E. Tate (pp. 5289-5299).
A generalised additive modelling (GAM) approach is used to model daily concentrations of nitrogen oxides (NO X), nitrogen dioxide (NO2), carbon monoxide (CO), benzene and 1,3-butadiene at a busy street canyon location in central London. The models were developed for the period July 1998–June 2005 using appropriate meteorological and road traffic covariates. For all models, the complex and localised wind-flow patterns resulting from the street canyon location of the monitoring site, which can be difficult to model deterministically, have a large influence on the model predictions. It is shown that GAMs built using simple covariates explain a large amount of the daily variation for these pollutants (mean r2=0.86). It is found that concentrations of benzene and 1,3-butadiene have declined in line with detailed calculations of emissions trends, with some evidence to suggest that reductions in benzene have been greater than estimated reductions in emissions. Although measured concentrations of NO X have declined from 1998 to 2005, much of the decline appears to be associated with reductions in overall traffic and meteorological factors rather than reduced emissions of NO X. Unadjusted NO X trends show a 28.6% reduction (95% confidence interval from 21.2% to 35.8%) from 1998 to 2005, whereas meteorologically adjusted trends show a 19.3% decline (95% confidence interval from 14.8% to 23.5%) over this period. Analysis shows that there were a higher number of occasions in the early part of the time series that led to strong recirculation of exhaust emissions and higher NO X concentrations at this location, thus affecting observed trends in concentration.

Keywords: Time series modelling; Trend; Urban air pollution; Generalised additive mixed model; Street canyon; Bootstrap


Validation of the Polyphemus platform on the ETEX, Chernobyl and Algeciras cases by Quélo Denis Quélo; Monika Krysta; Marc Bocquet; Olivier Isnard; Yannick Minier; Bruno Sportisse (pp. 5300-5315).
The objective of this article is to investigate the validity of a modeling system developed for forecasting atmospheric dispersion, thePolyphemus platform, with a special focus on radionuclides. The platform is briefly described and model-to-data comparisons are reported for three cases: the ETEX campaign, the Chernobyl accident and the Algeciras release. The results are similar to those usually given in the literature by state-of-the-art models. Some preliminary sensitivity analysis indicates the main sources for uncertainties.

Keywords: Radionuclides; Chernobyl; Algeciras; ETEX; Air quality modeling; P; olyphemus; P; olair; 3D; Long-range transport


Associations between particle physicochemical characteristics and oxidative capacity: An indoor PM10 study in Beijing, China by Longyi Shao; Jinjuan Li; Houyin Zhao; Shushen Yang; Hui Li; Weijun Li; Tim Jones; Keith Sexton; BeruBe Kelly BéruBé (pp. 5316-5326).
A study was undertaken to determine the use of a plasmid DNA scission assay to evaluate the causal relationships between particle oxidative capacity and physico-chemistry. Field emission scanning electron microscopy (FESEM), image analysis (IA) and inductively coupled plasma-mass spectrometry (ICP-MS) were employed to investigate the physico-chemical characteristics of indoor PM10 (particulate matter with an aerodynamic diameter of 10μm or less) in Beijing, China. Six PM10 samples (indoor smoker's living room; indoor non-smoker's living room and kitchen; and outdoor Beijing city; winter versus summer) were selected to represent typical indoor Beijing PM10 environments that contain high particle mass. The PM10 collected from a kitchen and two smoker's homes had the lowest TD50 (toxic dosage of PM10 causing 50% plasmid DNA damage), being as low as 45μgml−1 (kitchen) and 100μgml−1 (living room), which suggests a high oxidative capacity, with the PM10 generated in kitchens appearing to be the most toxic. The indoor PM10 from the non-smoker's home and outdoor PM10 samples demonstrated high TD50 values and were deemed less bioreactive (i.e. caused limited DNA damage). FESEM observations revealed that four types of particle species were prevalent in Beijing indoor PM10; soot aggregates, minerals, coal fly ash and unknown fine particles. IA showed that higher percentages of soot and unknown fine particles were associated with the lower TD50 values, suggesting that soot and the unknown fine particles may be important components responsible for the observed plasmid DNA damage. The water-soluble trace elements were negatively correlated with the TD50 values, implying that the DNA damage may be attributed to the water-soluble fraction of the PM10. Water-soluble zinc revealed the best relationship with the TD50 values than other analyzed elements, signifying it may play a role in driving the oxidative damage.

Keywords: Plasmid DNA assay; Oxidative stress; Trace element; Indoor air; PM; 10


Emission of trans, trans-2,4-decadienal from restaurant exhausts to the atmosphere by H.-H. Hsi-Hsien Yang; S.-M. Shu-Mei Chien; H.-L. Hui-Ling Lee; M.-R. Mu-Rong Chao; H.-W. Hong-Wei Luo; Dennis P.H. Hsieh; W.-J. Wen-Jhy Lee (pp. 5327-5333).
Cooking exhausts may contribute significant organic compounds to the atmosphere. It has been shown that trans, trans-2,4-decadienal ( tt-DDE) is an important toxic compound in cooking oil fumes (COF). In this study, the emissions of tt-DDE were quantified in both gaseous and particulate phases of three kinds of restaurant exhausts (Chinese, western and barbecue). Samples of exhausts were collected with a sampling system meeting the criteria of US EPA Modified Method 5. The tt-DDE was analyzed by HPLC–MS/MS. The results indicate that the emission factors of tt-DDE in terms of μgcustomer−1 were in sequence: barbecue (1990)>Chinese (570)>western (63.8). The average proportion of tt-DDE in the particulate phase of the exhausts was 83% for the 16 investigated restaurants. Evidently, the majority of tt-DDE in the exhausts was in the particulate phase. There was no evident correlation found between phase distribution of tt-DDE and exhaust temperature in the restaurants investigated. The efficiencies of removal of particulate tt-DDE by air pollution control devices (APCDs) were assessed. The removal efficiencies of electrostatic precipitator (ESP), ESP and activated carbon in series, and wet scrubber were 64.2%, 86.3% and 71.3%, respectively.

Keywords: trans; ,; trans; -2,4-Decadienal; Restaurant discharges; Emission factor; Removal efficiency


On-road emission characteristics of heavy-duty diesel vehicles in Shanghai by Changhong Chen; Cheng Huang; Qiguo Jing; Haikun Wang; Hansheng Pan; Li Li; Jing Zhao; Yi Dai; Haiying Huang; Lee Schipper; David G. Streets (pp. 5334-5344).
On-road vehicle tests of nine heavy-duty diesel trucks were conducted using SEMTECH-D, an emissions measuring instrument provided by Sensors, Inc. The total length of roads for the tests was 186km. Data were obtained for 37,255 effective driving cycles, including 17,216 on arterial roads, 15,444 on residential roads, and 4595 on highways. The impacts of speed and acceleration on fuel consumption and emissions were analyzed. Results show that trucks spend an average of 16.5% of the time in idling mode, 25.5% in acceleration mode, 27.9% in deceleration mode, and only 30.0% at cruise speed. The average emission factors of CO, total hydrocarbons (THC), and NO x for the selected vehicles are (4.96±2.90), (1.88±1.03) and (6.54±1.90)gkm−1, respectively. The vehicle emission rates vary significantly with factors like speed and acceleration. The test results reflect the actual traffic situation and the current emission status of diesel trucks in Shanghai. The measurements show that low-speed conditions with frequent acceleration and deceleration, particularly in congestion conditions, are the main factors that aggravate vehicle emissions and cause high emissions of CO and THC. Alleviating congestion would significantly improve vehicle fuel economy and reduce CO and THC emissions.

Keywords: Heavy-duty diesel vehicles; On-road emission testing; SEMTECH-D; Shanghai; Traffic congestion


Estimating micrometeorological inputs for modeling dispersion in urban areas during stable conditions by Marko Princevac; Akula Venkatram (pp. 5345-5356).
We examine the performance of three methods to estimate the surface friction velocity and the Monin–Obukhov (MO) length in stable conditions. Estimates from these methods are compared with measurements made at two urban sites: the Wilmington site located in the middle of an urban area, and the VTMX site located on a sloping, smooth area in Salt Lake City. The first method uses the mean wind at a single height (Single U or SU), the second uses the wind speed at a single level and the temperature difference between two levels (U delta T or UDT), and the third method uses two levels of wind speed and temperature (delta U delta T or DUDT). The performance of the SU and UDT methods in estimating u* are comparable. The SU method yields better estimates of the MO length than the UDT method does. The DUDT method performs poorly in estimating both u* and L. The major conclusions of this study are that (1) measurements of mean winds and temperatures at one or two levels at an urban location can provide adequate estimates of micrometeorological variables required in modeling dispersion in the stable boundary layer, and (2) methods based on using differences in temperatures and velocities between two levels can provide unreliable estimates of these variables because these differences can be overwhelmed by inevitable uncertainties in the measurement of mean variables.

Keywords: Friction velocity; Monin–Obukhov length; Stable boundary layer; Wilmington; VTMX


Evaluation of traffic-producing turbulence schemes within Operational Street Pollution Models using roadside measurements by Efisio Solazzo; Sotiris Vardoulakis; Xiaoming Cai (pp. 5357-5370).
Low wind scenarios are associated with the worst air pollution episodes in urban street canyons. Under these conditions, operational dispersion models often over-predict pollutant concentration. Traffic-producing turbulence (TPT) becomes dominant in mixing and diluting traffic-related pollutants under low wind speed conditions. Determining the TPT effect on the flow and dispersion patterns within urban street canyons is crucial for the development of detailed operational dispersion models for assessing urban air quality. Several spatially averaged TPT formulations have been recently proposed in the literature. However, only a few attempts have been made so far to incorporate different TPT schemes into operational dispersion models and evaluate their performance using measurements.In this paper, several TPT schemes presented in literature were evaluated. Two TPT schemes were implemented in the well-validated Windows version of the Danish Operational Street Pollution Model (WinOSPM). Both formulations were evaluated using six independent datasets of roadside CO concentrations collected in European cities. Statistical and sensitivity analyses were undertaken to test the performance of the different formulations. The results showed that the overall model performance was significantly sensitive to the TPT schemes adopted. The model performance improved when a detailed characterisation of the TPT, depending on the density of road traffic, was used.

Keywords: Dispersion modelling; WinOSPM; Street canyon; Urban air pollution; Traffic-producing turbulence


Composition and emissions of VOCs in main- and side-stream smoke of research cigarettes by Simone M. Charles; S.A. Batterman; Chunrong Jia (pp. 5371-5384).
It is well known that mainstream (MS) and sidestream (SS) cigarette smoke contains a vast number of chemical substances. Previous studies have emphasized SS smoke rather than MS smoke to which smokers are exposed, and most have used chamber tests that have several disadvantages such as wall losses. Emissions from standard research cigarettes have been measured, but relatively few constituents have been reported, and only the 1R4F (low nicotine) cigarette type has been tested. This study provides a comprehensive characterization of total, MS and SS smoke emissions for the 1R5F (ultra low nicotine), 2R4F (low nicotine), and 1R3F (standard nicotine) research cigarettes research cigarettes, including emission factors for a number of toxic compounds (e.g., benzene) and tobacco smoke tracers (e.g., 2,5-dimethyl furan). Emissions of volatile organic compounds (VOCs) and particulate matter (PM) are quantified using a dynamic dilution emission measurement system that is shown to produce accurate, rapid and reproducible results for over 30 VOCs and PM. SS and MS emissions were accurately apportioned based on a mass balance of total emissions. As expected, SS emissions greatly exceeded MS emissions. The ultra low nicotine cigarette had lower emissions of most VOCs compared to low and standard nicotine cigarettes, which had similar emissions. Across the three types of cigarettes, emissions of benzene (296–535μgcig−1), toluene (541–1003μgcig−1), styrene (90–162μgcig−1), 2-dimethyl furan (71–244μgcig−1), naphthalene (15–18μgcig−1) and other VOCs were generally comparable to or somewhat higher than literature estimates using chamber tests.

Keywords: Cigarettes; Emissions; Exposure; Tobacco smoke; Tracers; Volatile organic compounds (VOCs)


New approaches to study the relationship between stomatal conductance and environmental factors under Mediterranean climatic conditions by Marcello Vitale; Silvia Anselmi; Elisabetta Salvatori; Fausto Manes (pp. 5385-5397).
The most frequently models used (Ball–Berry and Jarvis-type models) to estimate stomatal conductance (Gs) values have limitations when applied to plants growing in Mediterranean climate. To overcome these limitations, several statistical methodologies (Multiple Linear Regression, Neural Net Analysis (NNA)) were used to build models to predict Gs. However, all these models were unable to integrate the physiological response of plants to the overall limiting environmental parameters in our Mediterranean site especially during the summer drought. With this in mind, it is relevant to find alternative approaches which link Gs response to environmental limitations of plants. In this paper, we demonstrate that: (1) the different linear and nonlinear statistical approaches used significantly affect the weights of the environmental variables which are utilized in semi-empirical Gs models; (2) a tight relationship exists between summer values of Gs and the rate of accumulated precipitations ( α) in the first 5 months of the year, thus allowing to predict Gs in a quantitative way; and (3) the latter is also related to different water-use strategies adopted by plants in response to drought stress in the summer period. Because α is easily calculated, it is an interesting parameter for the Gs modelling addressed to understand many important aspects of the plant–environment interactions, such as water relations and pollutant uptake.

Keywords: Drought stress; Ozone uptake; Stomatal conductance; Multivariate analysis; Mediterranean oaks


A socio-economic method for estimating future air pollutant emissions—Chicago case study by Zhining Tao; Allen Williams; Kieran Donaghy; Geoffrey Hewings (pp. 5398-5409).
This paper presents the development of an econometric-emission model to formulate future anthropogenic emission inventories for different societal and climate change scenarios. Our approach is to formulate the emission projections for a given scenario into growth factors that can be used to project forward the 1999 National Emission Inventory (NEI99). The process involves (1) mapping NEI99 source classification code (SCC)-based emissions into the sector or standard industrial classification (SIC)-based representation used by the econometric model, (2) developing a sectoral emission intensity (EMI) defined as the sector emissions per unit of sector economic output and the mechanism to consider EMI variations over time, (3) using the resulting EMI with econometric models and future emission activities to project future emissions, (4) and then mapping the emissions back to the original NEI99 format. As a case study, we apply the model to project emissions in the Chicago metropolitan area. The results show that the model is a fast, flexible, yet reasonable tool to produce a wide range of emission scenarios that are specific to regions, and would prove valuable for future air quality and other impact studies.

Keywords: Emission intensity; Emission scenario; Regional input–output econometric model


Fine particle concentrations and composition during wintertime inversions in Logan, Utah, USA by Philip J. Silva; Eric L. Vawdrey; Misty Corbett; Mark Erupe (pp. 5410-5422).
During Winter 2004, a series of elevated PM2.5 events occurred in Logan, Utah, coinciding with strong winter inversions. This period resulted in 17 exceedances of the 24-h PM2.5 standard, and some of the highest PM2.5 mass loadings recorded in the United States, including 9 days of 24-h PM2.5 measurements over 100μgm−3. During the 3-month period, we monitored the size and mass concentrations of airborne particles using an aerosol mass spectrometer. PM2.5 concentrations were dominated by the formation of ammonium nitrate, accounting for over 50% of the non-refractory aerosol matter throughout the study and 80% on the highest pollution days. Another 15–20% of the particulate matter was composed of organic carbon. The high particle concentration loadings in Utah's Cache Valley result from a combination of unfavorable meteorology dominated by a severe cold-temperature inversion, a mix of rural and urban emission sources, and a confined geographical area. As a rapidly growing formerly rural area, the Cache Valley is representative of future air pollution problems facing areas of the interior west undergoing rapid urbanization.

Keywords: PM; 2.5; Ammonium nitrate; Aerosol mass spectrometry; Agriculture


Trend, seasonal and multivariate analysis study of total gaseous mercury data from the Canadian atmospheric mercury measurement network (CAMNet) by Christian Temme; P. Blanchard; A. Steffen; C. Banic; S. Beauchamp; L. Poissant; R. Tordon; B. Wiens (pp. 5423-5441).
Long-term monitoring data of total gaseous mercury (TGM) concentrations from the Canadian Atmospheric Mercury Measurement Network (CAMNet) were analysed for temporal trends, seasonality and comparability within the network and compared to other network and model results. Data collected from 11 Canadian measurement sites between 1995 and 2005 were analysed. Sites within CAMNet were characterized by principle component analysis (PCA) into four main categories. For the first time since automated TGM measurements have been made within CAMNet, this paper reveals statistically significant decreasing TGM concentrations from rural locations in Canada during this time period. The largest declines were observed close to the urban areas of Toronto and Montreal, where levels fell by 17% at Point Petre, and 13% at St. Anicet, respectively. Many of the TGM changes are comparable with the overall trends observed in total mercury concentrations in precipitation, for similar time periods, at co-located or nearby National Atmospheric Deposition programme's Mercury Deposition Network (NADP-MDN) sites. The results show that these changes are mostly driven by local or regional changes in mercury emissions. Other sites within CAMNet reflect reported changes in hemispherical global background concentrations of airborne mercury, where slight decreases or no statistically significant trend in TGM concentrations exist over the same time period.

Keywords: Total gaseous mercury; Monitoring; Canadian atmospheric mercury measurement network; Time-series analysis; Long-term trend


On the performance of a semi-continuous PM2.5 sulphate and nitrate instrument under high loadings of particulate and sulphur dioxide by Wai Shing Wu; Tao Wang (pp. 5442-5451).
The need for highly time-resolved data on atmospheric aerosol composition has prompted the development of several semi-continuous techniques in recent years. It is necessary to evaluate the performance of these new techniques under different meteorological and chemical conditions. We report on the results of intercomparison between a new commercial PM2.5 semi-continuous sulphate and nitrate instrument (AIM, URG9000B) and filter-based technique. The study was carried out in the summer of 2005 in two polluted suburban/rural areas near Shanghai and Beijing, China, yielding unique results on the performance of this instrument in more polluted environments compared to most of the previously reported studies. The two methods had a good ( R2>0.67) overall correlation for sulphate and nitrate, but showed discrepancies in absolute concentrations. At low levels of sulphate (<20μgm−3) and SO2 (<30ppbv), the AIM data agreed with the filter result in Beijing (AIM=0.97×filter+0.60, R2=0.94). However, the semi-continuous instrument gave much higher sulphate values at high SO2 concentrations (in Shanghai), which was due to a positive interference from SO2 that broke through the denuder. At high sulphate loading, on the other hand, the AIM gave a much smaller sulphate reading, which was apparently due to an insufficient supply of water vapor to dissolve all the soluble ions under high aerosol loadings. For nitrate, while the two methods showed a good agreement in Shanghai (AIM=0.83×filter+0.00, R2=0.96), evaporative loss from the filters at high temperatures and negative bias in the AIM at high particle loading complicated the correlation in Beijing. Our study points out the need for careful evaluation and modification of the AIM for use in highly polluted environments. Under clean to moderately polluted conditions, the AIM can provide useful, highly time-resolved sulphate and nitrate data.

Keywords: Sulphate; Nitrate; Beijing; Shanghai; AIM


Increase in surface ozone at rural sites in the western US by Dan Jaffe; John Ray (pp. 5452-5463).
We evaluated O3 data for the period 1987–2004 from 11 rural and remote sites in the north and western US, including two sites in Alaska. All sites show a seasonal cycle with a spring or spring-summer maximum. By deseasonalizing the data, we are better able to identify seasonal and spatial patterns and long-term trends. For most of the locations in the western US that we considered, there are significant inter-site correlations in the deseasonalized monthly means. This indicates that there are large scale factors that influence the monthly mean O3 concentrations across the western US. At seven out of nine sites in the western US, there is a statistically significant increase in O3 with a mean trend of 0.26ppbvyear−1 (range at the seven sites is 0.19–0.51ppbvyear−1). At three of the sites, we examined the data in more detail to find that the trends are present in all seasons. At the two sites in Alaska, no clear pattern was found. At the one ozonesonde site in the western US with long-term observations (Boulder, Colorado), no significant trend was identified. However, the statistical power in the ozonesonde analysis is limited due to the low frequency of ozonesonde launches. Temperature changes can explain only a fraction of the surface O3 trend. We consider several possible explanations for these trends, including: increasing regional emissions, changes in the distribution of emissions, increasing biomass burning or increasing global background O3. With the available data, we are not able to unambiguously identify the cause for increasing O3 in the western US

Keywords: Ozone; National parks; Western US; Tropospheric chemistry


Spatial variability and population exposure to PM2.5 pollution from woodsmoke in a New South Wales country town by D.L. Robinson; J.M. Monro; E.A. Campbell (pp. 5464-5478).
A portable radiance research nephelometer was used to measure the variation in woodsmoke pollution in Armidale (a small town of 22,000 people), New South Wales, Australia, on 14 winter nights in 1996. Winter nights are characterised by inversions that trap the air within the valley and reduce winds to very low speeds (averaging 0.15ms−1). Pollution varied considerably with location. Mean scattering coefficients (bsp/10km) for 14 measurement nights ranged from less than 1.0 on the undeveloped fringes of the city to 8.7, the latter representing a 14-night average of 200μgm−3 of PM2.5. Pollution was generally highest in the residential areas on either side of the valley, where the smoke was generated, rather than the low-lying central creeklands. In places, average pollution levels increased 4-fold within 41m. The correlation between nephelometer and gravimetric pollution measurements ranged 0.95–0.99. The presence of large, sudden but repeatable changes in air pollution, and high correlations between nephelometer and gravimetric measurements, indicate that mobile pollution monitoring devices provide a useful and accurate estimate of spatial variability. Estimated exposure for the town as a whole was 1.02 for the 6 months from April to September, 0.25 in October as heater use declines, and 0.12 in normal summer months. For comparison, published 25th, 50th and 75th percentiles of the distribution of nephelometer coefficients in Sydney were 0.15, 0.24 and 0.37, respectively. Thus annual exposure to PM2.5 pollution in Armidale from woodsmoke is more than double that from all sources in Sydney, a city of 4 million. Overseas estimates of 6% increased mortality for each additional 10μgm−3 of PM2.5 suggest that wood heaters in Armidale may increase mortality in Armidale by about 7%, with estimated cost of about $4270 per woodheater per year. Alternative cheap and environmentally friendly methods of keeping houses warm in winter, such as solar heating, should therefore be developed.

Keywords: Wood smoke; PM2.5; PM10; Spatial variability; Health costs; Mapping


Flux estimates and OH reaction potential of reactive biogenic volatile organic compounds (BVOCs) from a mixed northern hardwood forest by John Ortega; Detlev Helmig; Alex Guenther; Peter Harley; Shelley Pressley; Christoph Vogel (pp. 5479-5495).
Diurnal branch-level emission rates of biogenic volatile organic compounds (BVOC) including isoprene, monoterpenes (MT), and sesquiterpenes (SQT) were determined at the University of Michigan Biological Station for the tree species red maple ( Acer rubrum), red oak ( Quercus rubra), paper birch ( Betula papyrifera), white pine ( Pinus strobus), and big tooth aspen ( Populus grandidentata). These emission rates were combined with detailed biomass distribution and meteorological data and incorporated into the canopy model, model of emissions of gasses and aerosols from nature (MEGAN), for estimating whole-canopy fluxes of isoprene. The modeled half-hour fluxes(mgCm-2h-1) and cumulative seasonal fluxes(mgCm-2) compared favorably with results from direct, canopy-level eddy covariance (EC) isoprene measurements; modeled cumulative seasonal flux deviated less than 30% from the EC results. Significant MT emissions were found from four of the five tree species. MT emissions from three of these were both light- and temperature-dependent and were approximately one order of magnitude greater than light-independent MT emissions. SQT emissions were identified from three of the five tree species. The model was modified to incorporate SQT and both light-dependent and light-independent MT emissions for determining fluxes. Isoprene comprised>95% of the total terpenoid flux with MT and SQT comprising 4% and 0.3%, respectively. The average cumulative fluxes (inmgCm-2) from June through September were 2490 for isoprene, 105 for MT, and 7 for SQT. A simple box model analysis was used to estimate the contribution of the isoprene, MT, and SQT emissions to the total OH reactivity. These results confirm that isoprene dominates OH reactions especially during daytime hours. Emissions of reactive MT and SQT increase the BVOC+OH reactivity, but are still lower than estimates of BVOC fluxes at this site necessary for affecting OH reactivity to the significant degree suggested by recent reports.

Keywords: VOC; Oxidant; Monoterpene; Sesquiterpene; Fluxes; Biogenic emission modeling; Isoprene


Simulation of pollutant dispersion for low wind conditions in stable and convective planetary boundary layer by Daniela Buske; Marco T. Vilhena; Davidson M. Moreira; Tiziano Tirabassi (pp. 5496-5501).
The present study proposes a steady-state mathematical model for dispersion of contaminants in low winds that takes into account the along-wind diffusion, but it does not consider the variable wind direction typical of low wind. The solution of the advection–diffusion equation for these conditions is obtained applying the generalized integral Laplace transform technique (GILTT) method and the eddy diffusivities are functions of distance from the source. The performance of the model was evaluated against the field experiments at the Idaho National Engineering Laboratory, the Lilleström dataset and during convective conditions at the Indian Institute of Technology.

Keywords: Low winds; Advection–diffusion equation; Air pollution modeling; GILTT method; Analytical solution


Hydroxyl (OH) radical production rates in snowpacks from photolysis of hydrogen peroxide (H2O2) and nitrate (NO3−) by J.L. France; M.D. King; J. Lee-Taylor (pp. 5502-5509).
Atmospheric chemistry directly above snowpacks is strongly influenced by ultraviolet (UV) radiation initiated emissions of chemicals from the snowpack. The emission of gases from the snowpack to the atmosphere is in part due to chemical reactions between hydroxyl radical, OH (produced from photolysis of hydrogen peroxide (H2O2) or nitrate (NO3−)) and impurities in the snowpack. The work presented here is a radiative-transfer modelling study to calculate the depth-integrated production rates of hydroxyl radical from the photolysis of hydrogen peroxide and nitrate anion in snow for four different snowpacks and for solar zenith angles 30°–90°. This work also demonstrates the importance of hydrogen peroxide photolysis to produce hydroxyl radical relative to nitrate photolysis with (a) different snowpacks, (b) different ozone column depths, and (c) snowpack depths. The importance of hydrogen peroxide photolysis over nitrate photolysis for hydroxyl radical production increases with increasing depth in snowpack, column ozone depth, and solar zenith angle. With a solar zenith angle of 60° the production of hydroxyl radical from hydrogen peroxide photolysis accounts for 91–99% of all hydroxyl radical production from hydrogen peroxide and nitrate photolysis.

Keywords: NO; 3; H; 2; O; 2; Ozone; Snow; Troposphere; Ice; Nitrate; Hydrogen peroxide; Hydroxyl; Radical


Henry's Law coefficients of chloropicrin and methyl isothiocyanate by Erica K. Worthington; Elisabeth A. Wade (pp. 5510-5515).
Henry's Law coefficients were measured for the first time for chloropicrin and methyl isothiocyanate (MITC) at 25°C in deionized water, in 0.10M NaCl, in 0.20M NaCl, and in pH 4.0 and 8.0 buffered solutions. For chloropicrin, the Henry's Law coefficient was 2.1±0.3atmM−1, and did not show significant pH dependence or dependence on ionic strength. For MITC, the coefficient was much smaller, 0.06±0.05atmM−1. The Henry's Law coefficient for MITC did show dependence on ionic strength, increasing to 0.14±0.05atmM−1 at 0.20M, but did not appear to depend on pH. MITC has a much stronger tendency to remain in solution than chloropicrin. The transport of chloropicrin from solution to the atmosphere is likely to be significant environmentally, while MITC shows a much lower rate of volatilization. When transferred to the atmosphere, oxidation and photochemical reactions are likely to dominate the transformation of both chloropicrin and MITC, rather than heterogenous reactions.

Keywords: Methyl isothiocyanate, MITC; Chloropicrin; Metam sodium; Henry's Law


A methodology for the quantification of the net African dust load in air quality monitoring networks by M. Escudero; X. Querol; J. Pey; A. Alastuey; Perez N. Pérez; F. Ferreira; S. Alonso; Rodriguez S. Rodríguez; E. Cuevas (pp. 5516-5524).
This paper proposes and validates a methodology for the quantification of the daily African PM load during dust outbreaks in southern Europe. The daily net dust load in PM10 attributable to an African episode in a given region can be obtained by subtracting the daily regional background (RB) level from the PM10 concentration value at an RB station. As demonstrated in this paper, the daily RB level can be obtained by applying a monthly moving 30th percentile to the PM10 time series at an RB station after a prior extraction of the data of the days with African dust transport. The daily PM10 RB levels obtained can be subtracted from the daily PM10 levels recorded at the same RB site only on days when the occurrence of African dust outbreaks was demonstrated, the difference being the daily net African dust load. It is thus possible to quantify the African dust contribution during an African PM event in southern Europe without the need for PM speciation.The validation of this methodology was performed by comparing the estimated net dust load during African dust outbreaks at three RB stations and the crustal load determined by chemical speciation of PM10 filters. The correlation ( r2>0.6) and the equivalence (correlation lines’ slopes ∼1) were significant in the three cases.

Keywords: Mineral dust; Natural episodes; PM10; Daily limit value


A new methodological approach: The combined use of two-stage streaker samplers and optical particle counters for the characterization of airborne particulate matter by Federico Mazzei; Franco Lucarelli; Silvia Nava; Paolo Prati; Gianluigi Valli; Roberta Vecchi (pp. 5525-5535).
We describe a new experimental methodology based on the contemporary use of two-stage continuous streaker samplers and optical particle counters. This is a complementary approach to size-segregated particulate matter (PM) sampling, and it is able to give information on the elemental size distribution and to assess the contribution of major PM source to size bins. PM samples in the fine and coarse fraction of PM10 have been collected by a two-stage streaker sampler and analyzed by particle-induced X-ray emission (PIXE) to obtain elemental concentration time series with hourly resolution. PM sources and profiles were singled out by positive matrix factorization (PMF). A multi-linear regression of size-segregated number of particles versus the sources, resolved by PMF, made possible the apportionment of size-segregated particles number in a fast and direct way. Results obtained in three sampling sites, located in different urban districts are discussed.

Keywords: Particulate matter; Streaker sampler; Optical counter; PIXE; PMF

Corrigendum to “Estimated long-term outdoor air pollution concentrations in a cohort study” by Rob Beelen; Gerard Hoek; Paul Fischer; Piet A. van den Brandt; Bert Brunekreef (pp. 5552-5552).
Corrigendum to “The impact of NO x, CO and VOC emissions on the air quality of Zurich airport” by Schurmann Gregor Schürmann; Schafer Klaus Schäfer; Carsten Jahn; Herbert Hoffman; Martina Bauerfeind; Emanuel Fleuti; Rappengluck Bernhard Rappenglück (pp. 5553-5554).
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