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Atmospheric Environment (v.42, #6)

Editorial board (pp. i).

Measurement of CO₂, CO, SO₂, and NO emissions from coal-based thermal power plants in India by N. Chakraborty; I. Mukherjee; A.K. Santra; S. Chowdhury; S. Chakraborty; S. Bhattacharya; A.P. Mitra; C. Sharma (pp. 1073-1082).

Measurements of CO₂ (direct GHG) and CO, SO₂, NO (indirect GHGs) were conducted on-line at some of the coal-based thermal power plants in India. The objective of the study was three-fold: to quantify the measured emissions in terms of emission coefficient per kg of coal and per kWh of electricity, to calculate the total possible emission from Indian thermal power plants, and subsequently to compare them with some previous studies. Instrument IMR 2800P Flue Gas Analyzer was used on-line to measure the emission rates of CO₂, CO, SO₂, and NO at 11 numbers of generating units of different ratings. Certain quality assurance (QA) and quality control (QC) techniques were also adopted to gather the data so as to avoid any ambiguity in subsequent data interpretation. For the betterment of data interpretation, the requisite statistical parameters (standard deviation and arithmetic mean) for the measured emissions have been also calculated. The emission coefficients determined for CO₂, CO, SO₂, and NO have been compared with their corresponding values as obtained in the studies conducted by other groups. The total emissions of CO₂, CO, SO₂, and NO calculated on the basis of the emission coefficients for the year 2003–2004 have been found to be 465.667, 1.583, 4.058, and 1.129Tg, respectively.

Keywords: Thermal power plants; On-line measurement; Direct and indirect GHG; Emission coefficient

Large eddy simulation of wind field and plume dispersion in building array by R.F. Shi; G.X. Cui; Z.S. Wang; C.X. Xu; Z.S. Zhang (pp. 1083-1097).

This paper presents numerical simulation of wind field and contaminant dispersion in the flow over a group of buildings by large eddy simulation (LES) with higher accuracy finite volume method (FVM) for numerical discretization of governing equation and with immersed boundary method (IBM) at building surfaces. The paper is aimed at proposing a numerical method which can deal with the complex turbulent flow and contaminant dispersion inside a group of buildings. The geometry of the building layout and flow parameters are taken from the wind tunnel experiments by Davidson et al. [1996. Wind tunnel simulations of plume dispersion through groups of obstacles. Atmospheric Environment 30 (22), 3715–3731] so that the feasibility and reliability of the numerical method and code can be examined by comparison between numerical results and experimental measurements with confidence. The flow patterns and contaminant dispersion inside the group of buildings are shown in agreement with the description of Davidson et al. [1996. Wind tunnel simulations of plume dispersion through groups of obstacles. Atmospheric Environment 30 (22), 3715–3731]. The numerical prediction of the statistical properties of contaminant dispersion, e.g. the mean concentration distributions, lateral and vertical spreads of the contaminant an so forth, is in good agreement with wind tunnel experiment measurements. The numerical study of this testing case reveals a number of issues which should be considered in application of LES to such complex turbulent flows in environment engineering, e.g. spatial resolution, reasonable subgrid stress model and the turbulent intensity in atmospheric boundary layer.

Keywords: Large eddy simulation; Finite volume method; Immersed boundary method; Building array; Contaminant dispersion

Quality and performance of a PM10 daily forecasting model by Ernst Stadlober; Siegfried Hörmann; Brigitte Pfeiler (pp. 1098-1109).

Particularly in the cold season unfavorable dissemination conditions of the ambient air lead to higher-than-average PM10concentrations in parts of the western Alpe-Adria-Region, covering the provinces South Tyrol, Carinthia and Styria. Therefore, EU pollution standards cannot be met in the cold season and partial traffic regulation measures are taken in Bolzano, Klagenfurt and Graz, the three capitals in this region. Decision making for these regulations may be based on the average PM10concentration of the next day provided that reliable forecasts of these values can be offered. In the present paper we show how multiple linear regression models combining information of the present day with meteorological forecasts of the next day can help forecasting daily PM10concentrations for sites located in the three cities. Special emphasis is given to an appropriate selection of the regressor variables readily available as measured values, factors or meteorological forecasts suitable in operational mode. To reflect the quality of the forecast properly, we define a quality function where prediction errors near the threshold PM10of50μgm-3 are assumed to be more severe than errors in regions that are either far below or above the threshold. Since December 2004, the forecasts are used as a monitoring and information tool in Graz. Our daily forecasts have been carried out in cooperation with the meteorologists from the ZAMG Styria (Styrian meteorological office). The investigations in terms of the quality function and according possible decision rules show that our prediction models may support future decisions concerning possible traffic restrictions not only in Graz, but also in Bolzano and Klagenfurt.

Keywords: Forecasting PM10; Multiple linear regression; Meteorology; Quality function

High and low volume sampling of particulate matter at sites with different traffic profiles in the Netherlands and Germany: Results from the HEPMEAP study by Nicole A.H. Janssen; Kees Meliefste; Oliver Fuchs; Stephan K. Weiland; Flemming Cassee; Bert Brunekreef; Thomas Sandstrom (pp. 1110-1120).

Within the EU project “Health Effects of Particles from Motor Engine Exhaust and Ambient Pollution” (HEPMEAP), ambient particulate matter (PM) was collected at sites, with varying traffic density and sources of PM emissions, in the Netherlands and Munich, Germany. In the Netherlands, measurements were conducted close to four schools which had participated 4 years earlier in a study on respiratory health of children attending schools near motorways. In Munich, measurements were conducted at a high traffic inner city and a suburban background (low traffic) site. Measurements were spaced over a period of approximately 1 year. Collection of PM was conducted using both high volume and low volume impaction methods. In addition to PM mass, PM-absorbance (‘soot’) and NO₂ were measured as indicators of fossil fuel combustion. PM_2.5 and PM₁₀ concentrations calculated from the high volume collections were highly correlated with PM_2.5 and PM₁₀ concentrations measured simultaneously by low volume samplers ( R² 0.87–0.94). Both high and low volume measurements showed little difference in semi annual average PM mass concentrations between sites within each country, with PM concentrations at the highest exposed sites being only about 10–30% higher compared to the lowest exposed sites. Contrasts for PM-absorbance and NO₂ were significantly higher than for PM mass (70–90% in the Netherlands and 90–167% in Germany). This demonstrates a higher impact of traffic on these components compared to PM mass.

Keywords: Particles; Air pollution; Traffic; Toxicology; Epidemiology

The impact of fireworks on airborne particles by Roberta Vecchi; Vera Bernardoni; Diana Cricchio; DAlessandro Alessandra D’Alessandro; Paola Fermo; Franco Lucarelli; Silvia Nava; Andrea Piazzalunga; Gianluigi Valli (pp. 1121-1132).

Fireworks are one of the most unusual sources of pollution in atmosphere; although transient, these pollution episodes are responsible for high concentrations of particles (especially metals and organic compounds) and gases. In this paper, results of a study on chemical–physical properties of airborne particles (elements, ions, organic and elemental carbon and particles size distributions) collected during a fireworks episode in Milan (Italy) are reported. Elements typically emitted during pyrotechnic displays increased in 1h as follows: Sr (120 times), Mg (22 times), Ba (12 times), K (11 times), and Cu (6 times). In our case study, Sr was recognised as the best fireworks tracer because its concentration was very high during the event and lower than, or comparable with, minimum detection limits during other time intervals, suggesting that it was mainly due to pyrotechnic displays. In addition, particles number concentrations increased significantly during the episode (up to 6.7 times in 1h for the 0.5< d<1μm size bin). Contributions (e.g. Cu, elemental carbon and nitrogen oxides) to air pollution due to the large traffic volume registered during the same night were also singled out.The original application of Positive Matrix Factorisation and Multiple Linear Regression allowed, as far as we know, here for the first time, the quantification of the fireworks contribution to atmospheric particulate matter (PM) and the resolution of their chemical profile. The contribution of fireworks to the local environment in terms of PM₁₀ mass, elements and chemical components was assessed with 4-h time resolution. PM₁₀ mass apportioned by fireworks was up to 33.6μgm⁻³ (about 50% of the total PM₁₀ mass). Major contributors were elemental and organic carbon (2.8 and 8.1μgm⁻³, respectively) as well as metals like Mg, K, Sr, Ba, and Cu (0.4, 0.7, 0.07, 0.1, and 0.1μgm⁻³, respectively).

Keywords: Fireworks; Chemical composition; Number size distribution; PMF

Characterization of particle size distribution from diesel engines fueled with palm-biodiesel blends and paraffinic fuel blends by Y.-C. Yuan-Chung Lin; C.-F. Chia-Fon Lee; Tiegang Fang (pp. 1133-1143).

Biodiesels are promoted as alternative fuels and their applications in diesel engines have been investigated by many researchers. However, the particle size distribution emitted from heavy-duty diesel engines fueled with palm-biodiesel blended with premium diesel fuel and paraffinic fuel blended with palm-biodiesel has seldom been addressed. Thus, five test fuels were used in this work to study the particle size distribution: D100 (premium diesel fuel), B100 (100% palm-biodiesel), B20 (20vol% palm-biodiesel+80vol% D100), BP9505 (95vol% paraffinic fuel+5vol% palm-biodiesel) and BP8020 (80vol% paraffinic fuel+20vol% palm-biodiesel). A Micro-Orifice Uniform Deposit Impactor (MOUDI) equipped with aluminum filters was used to collect size-resolved samples. Experimental results indicated that palm-biodiesel blends and paraffinic fuel blends could improve combustion efficiency in diesel engines, but pure palm-biodiesel could cause incomplete combustion. Adding palm-biodiesel to diesel fuel would slightly increase particles with diameter <0.31μm but paraffinic fuel blends could decrease particles with diameter <1μm. The mass median diameter of overall particles (MMD_o) and σ_g,o are 0.439μm and 3.88 for D100; 0.380μm and 3.24 for B20; 0.465μm and 4.22 for B100; 1.40μm and 4.92 for BP9505; 1.46μm and 2.25 for BP8020. There are more particles with low aerodynamic diameters (diameter <0.31μm) in the exhaust of D100, B20 and B100 fuels. On the other hand, a greater fraction of particulate matter of BP9505 and BP8020 existed in coarse particles (diameter: 2.5–10μm). Energy efficiency also increases significantly by 12.3–15.1% with the introduction of paraffinic fuel blends into the engine. Nevertheless, paraffinic fuel blends also reduce the emission of particulate matters by 36.0–38.4%. Carbon monoxide was decreased by 36.8–48.5%. Total hydrocarbon is 39.6–41.7% less than diesel fuel combustion. Nitrogen oxides emission is about 5% lower for paraffinic fuel. These results show that paraffinic fuel can be very competitive and replaced diesel fuels in the future.

Keywords: Particle size distribution; Biodiesel; Paraffinic fuel; Energy efficiency; Emissions

A regional analysis of the fate and transport of mercury in East Asia and an assessment of major uncertainties by Li Pan; Gregory R. Carmichael; Bhupesh Adhikary; Youhua Tang; David Streets; Jung-Hun Woo; Hans R. Friedli; Lawrence F. Radke (pp. 1144-1159).

The fate and transport of mercury in East Asia is evaluated using the Sulfur Transport and dEposition Model (STEM)-Hg 3-D model. The model calculates mercury transport, transformation and deposition in East Asia during April 2001, the period of the ACE-Asia field campaign. Model predictions of dry and wet deposition are compared with the observations from 10 sampling sites in Japan. The model results are consistent with the observations, but tend to over-predict dry deposition. Sensitivity analysis of predicted results to uncertainties in the mercury reaction rates suggests that the oxidation of Hg⁰ to Hg(II) in the gas phase is the dominant pathway for atmospheric mercury removal processes. Simulation based on the most recently published reaction rate constants for gas phase oxidation of Hg⁰ to Hg(II) overestimates the production of Hg(II) in the gas phase. The regional mercury budget is calculated which shows that most of the reactive gas phase mercury (RGM) and particulate mercury (Hg_p) are deposited around the source region while 28.5Mg of Hg⁰ is exported out of East Asia during April 2001. The sensitivity analysis in the regional Hg budget to major uncertainties associated with Hg emission estimates and Hg chemistry are also evaluated.

Keywords: Mercury; STEM-Hg model simulation; East Asia; Budget; Uncertainties

Primary particles in ship emissions by Erik Fridell; Erica Steen; Kjell Peterson (pp. 1160-1168).

There is not much data available regarding particle emissions from ships. In this study the size distributions of particles in ship exhaust from three different ships in normal operational conditions were studied using a cascade impactor. The ships were equipped with slow- or medium-speed main engines and medium-speed auxiliary engines. The fuel was residual oil except for the auxiliary engines on one ship which used marine diesel. Large emissions and a dependence of the sulfur content in the fuel were observed. High amounts of relatively large particles (around 8μm) were observed. These are attributed to re-entrained soot particles from walls in the engine systems. A strong variation between different ships was observed for the particle-size distribution and for the dependence on engine load. The particle emissions were found to be reduced to about half, over the whole size range, by an SCR system. The total particle emission, measured after dilution, varied between 0.3 and 3gkWh⁻¹ depending on load, fuel and engine.

Keywords: Ship emissions; Particle emission; Emission factor; Particle-size distribution

A comprehensive performance evaluation of the air quality model BOLCHEM to reproduce the ozone concentrations over Italy by Mihaela Mircea; Massimo D’Isidoro; Alberto Maurizi; Lina Vitali; Fabio Monforti; Gabriele Zanini; Francesco Tampieri (pp. 1169-1185).

A comprehensive model evaluation has been conducted for BOLCHEM over the whole of Italy during four periods favorable to ozone photochemistry: 1–3 June, 1–4 July, 5–7 August and 20–24 January during the year 1999. Two photochemical mechanisms, SAPRC90 and CB-IV, have been employed to simulate the evolution of ozone, taking into account the Italian and European inventories and maritime emissions. The comparison of simulated and measured ozone concentrations demonstrates that the model is able to forecast well the daily variation of ozone with both mechanisms, in particular during the summer, when the ozone photochemistry is more active. The discrepancies between the ozone predicted with the SAPRC90 and CB-IV mechanisms are similar to those previously reported in the literature: SAPRC90 leading to higher ozone concentrations than CB-IV due to the differences in their representation of VOC mixture. However, for both photochemical mechanisms, the model skill scores are good, proving the reliability of the model for regional scale applications.

Keywords: Model validation; Ozone; BOLCHEM; Photochemistry; Air quality

Estimating aerosol light scattering at the Fresno Supersite by John G. Watson; Judith C. Chow; Douglas H. Lowenthal; Karen L. Magliano (pp. 1186-1196).

Aerosol light scattering (Bsp) was estimated from particle size and chemical measurements during the winter intensive period (15 December 2000–3 February 2001) at the Fresno Supersite as part of the California Regional PM₁₀/PM_2.5 Air Quality Study (CRPAQS). Bsp was underestimated by 41–46% from scanning mobility particle sizer (SMPS) and optical particle counter (OPC) particle size distributions depending on assumptions about refractive index and hygroscopic growth. Bsp was underestimated by 35% using the Interagency Monitoring of PROtected Visual Environments (IMPROVE) light extinction equation and by 25% using chemical size distributions measured with micro orifice uniform deposit impactor (MOUDI) cascade impactors and a Desert Research Institute (DRI) PM_2.5 sequential filter sampler (SFS). Underestimation of Bsp in Fresno was related to differences in the temperature and relative humidity (RH) at which various measurements were made. Evaporation of ammonium nitrate in the heated environment in which the SMPS and OPC instruments were located caused a reduction in particle size and number concentration. The MOUDI was operated outdoors at ambient temperature and RH, while a smart-heater equipped Radiance nephelometer was operated at RH <72%. Comparing estimated and measured Bsp required adjusting the SMPS, OPC, and MOUDI size distributions to the nephelometer RH. A systematic low-bias in estimated scattering suggests that organic aerosols may have contributed to hygroscopic growth. Consistent measurement strategies are needed to properly estimate aerosol light extinction under conditions such as those found in Fresno during winter.

Keywords: Particle light scattering; Supersite; Particle size distribution; Size-resolved chemistry

Methane emissions from three sea animal colonies in the maritime Antarctic by Renbin Zhu; Yashu Liu; Hua Xu; Jing Ma; Zhijun Gong; Sanping Zhao (pp. 1197-1205).

Methane (CH₄) emissions from domestic animals and their excreta have been extensively studied. However, little investigation has been carried out for CH₄ emissions from wild animal colonies. On a global scale, the most sea animal colonies are distributed in the maritime Antarctic. To evaluate temporal and spatial variations of CH₄ fluxes from sea animal colonies in the maritime Antarctic, net CH₄ fluxes were measured from the penguin, skua and seal colonies during the summertime of 2005/2006, using a static chamber technique. It was found that the CH₄ emission rates from these colonies were considerably high. The mean fluxes from the wet sites of penguin, skua and seal colonies were 230.7, 142.5 and 94.1μgm⁻²h⁻¹, respectively; the fluxes from the mesic sites were 123.8, 19.8 and 23.9μgm⁻²h⁻¹, respectively. The CH₄ fluxes were significantly affected by the deposition of the organic matter and nutrients from sea animal excreta, and soil water conditions. The single environmental factors cannot explain the seasonal variations of CH₄ fluxes from the colonies. The fluxes from the skua colony showed a daily variation with a maximum at noon or midnight and a minimum at 20:00h. These sea animal colonies are the “hotspots” of CH₄ emissions in the maritime Antarctic, and their fluxes could constitute an important part of the annual CH₄ budget for Antarctic tundra ecosystems.

Keywords: Methane flux; Sea animal colony; Antarctica; Penguin; Seal; Spatial variation

In-field greenhouse gas emissions from cookstoves in rural Mexican households by Michael Johnson; Rufus Edwards; Claudio Alatorre Frenk; Omar Masera (pp. 1206-1222).

The majority of estimates of the greenhouse gas emissions associated with changes from traditional to improved cookstoves in developing countries come from water-boiling tests (WBTs) conducted in simulated kitchens. Little is known about the bias in these estimates relative to typical stove use by residents in rural communities. To assess this bias, the reductions in emissions as a result of installation of an improved wood-burning “Patsari” stove were quantified in both simulated kitchens and field conditions in eight homes with open fire stoves and 13 homes with Patsari stoves in Purépecha communities of Michoacán, Mexico. The results demonstrate that nominal combustion efficiencies (NCEs) of open fire cookstoves were significantly lower ( p<0.001) in rural homes during daily cooking activities (89.7±2.0%) compared to WBTs in simulated kitchens (94.2±0.5%), which results in almost a doubling of the products on incomplete combustion (PICs) emitted. Since emissions from the rural residential sector are important in the modeling of atmospheric trace greenhouse gas concentrations in areas that rely on solid fuel use for primary energy provision, if these open fires reflect conditions in other areas of the world, substantial underestimation of emissions from open fires may be present in current emission databases. Conversely, NCEs for the improved Patsari stoves were significantly higher ( p<0.01) in rural homes during daily cooking activities (92.3±1.3%) compared to during WBTs in simulated kitchens (87.2±4.3%), as WBTs do not reflect cooking activities in rural homes. Thus the Patsari emits 25% less PICs per kg fuelwood used than the open fire, and carbon emission reductions of Patsari and similar improved stoves are also likely underestimated. Finally, in addition to a reduction in overall particulate emissions for rural homes during daily activities, the ratio of organic carbon (OC) to elemental carbon (EC) within the aerosol fraction decreased between the open fire and improved Patsari stoves. While the overall EC contribution for the brick Patsari was reduced, the fraction of EC increased relative to OC, which makes the overall warming implication more ambiguous given current uncertainties in warming and cooling potentials of these fractions.

Keywords: Emission factors; Black carbon; Cookstoves; Carbon savings; Global warming contributions

Atmospheric inorganic contaminants and their distribution inside stem tissues of Fraxinus excelsior L. by M. Mickaël Catinon; Sophie Ayrault; Laurent Daudin; Laure Sevin; Juliette Asta; Michel Tissut; Patrick Ravanel (pp. 1223-1238).

The elements present on and in 4-year-old stem of Fraxinus excelsior L. were analysed and estimated quantitatively. The superficial deposit on the bark is a complex mixture mainly composed of organic matter, mineral nutrients, clay and anthropogenic elements coming from the atmosphere. The elements present inside the stem tissues represent a total amount which is generally much higher than the superficial deposit. The distribution of elements such as Ca, K, Fe, Mn, Zn, Cu and Pb was shown by PIXE analysis in stem transversal cuttings, showing the presence of solid multimineral particles only inside the suber. A new strategy of mechanical tissues isolation on fresh stems was carried out in order to obtain high amounts of each tissue allowing an accurate ICP-MS analysis and estimation of >20 elements in each tissue. A concentration decreasing gradient was measured for each element from suber to wood and pith in good agreement with the PIXE results. In the dividing cells of the vascular cambium, elements concentrations were very high since the cell wall weight was minimal. When expressing the amounts of each element per bark area unit, the whole bark content was only twice the wood+pith content for the studied elements. All these results suggest that, in Fraxinus stems, the root uptake and xylem transport of elements are generally not intense enough to hide the atmospheric flux of mineral contaminants.

Keywords: Tree barks; Air pollution; Metals; Biomonitoring; ICP-MS; PIXE

Carbonaceous species emitted from handheld two-stroke engines by John Volckens; David A. Olson; Michael D. Hays (pp. 1239-1248).

Small, handheld two-stroke engines used for lawn and garden work (e.g., string trimmers, leaf blowers, etc.) can emit a variety of potentially toxic carbonaceous air pollutants. Yet, the emissions effluents from these machines go largely uncharacterized, constraining the proper development of human exposure estimates, emissions inventories, and climate and air quality models. This study samples and evaluates chemical pollutant emissions from the dynamometer testing of six small, handheld spark-ignition engines—model years 1998–2002. Four oil–gas blends were tested in each engine in duplicate. Emissions of carbon dioxide, carbon monoxide, and gas-phase hydrocarbons were predominant, and the PM emitted was organic matter primarily. An ANOVA model determined that engine type and control tier contributed significantly to emissions variations across all identified compound classes; whereas fuel blend was an insignificant variable accounting for <5% of the observed variation in emissions. Though emissions rates from small engines were generally intermediate in magnitude compared with other gasoline-powered engines, numerous compounds traditionally viewed as motor vehicle markers are also present in small engine emissions in similar relative proportions. Given that small, handheld two-stroke engines used for lawn and garden work account for 5–10% of total US emissions of CO, CO₂, NO _x, HC, and PM_2.5, source apportionment models and human exposure studies need to consider the effect of these small engines on ambient concentrations in air polluted environments.

Keywords: Source apportionment; Profile; Two-stroke; Biofuel; Lawn and garden; PAH; VOC; PM

Management of air quality monitoring using principal component and cluster analysis—Part I: SO₂ and PM₁₀ by J.C.M. Pires; S.I.V. Sousa; M.C. Pereira; M.C.M. Alvim-Ferraz; F.G. Martins (pp. 1249-1260).

The number of sites that constitute the air quality monitoring network (AQMN) of Oporto Metropolitan Area (Oporto-MA) should be optimised, aiming to reduce significant associated expenses. Ideally, only one monitoring site should operate in an area characterized by specific air pollution behaviour. The global aim of this study was to evaluate the performance of statistical methods for the more efficient management of AQMNs. The specific objectives were: (i) to identify city areas with similar air pollution behaviours; and (ii) to locate emission sources. Two statistical techniques, principal components analysis (PCA) and cluster analysis (CA), were applied to the mass concentrations of sulphur dioxide (SO₂) and particulate matter with an aerodynamic diameter less than 10μm (PM₁₀), collected in the AQMN of Oporto-MA from January 2003 to December 2005.Main results showed that the 10 monitoring sites of the AQMN could be coupled in six and no more than two groups for SO₂ and PM₁₀, respectively. It was found also that several monitoring sites covered city areas characterized by the same specific air pollution behaviour; suggesting then an ineffective management of the air quality monitoring system. The redundant equipment should be transferred to other monitoring sites allowing the enlargement of the monitored area. Only one main emission source of SO₂ was located and the six groups needed to characterize SO₂ mass concentrations were justified by the geographical location of that main emission source and by the variability of wind direction. Three main emission sources of PM₁₀ were located: (i) one inside the region defined by the AQMN, which significantly affected only two monitoring sites; and (ii) two outside that region, which affected all monitoring sites. One emission source located outside of the region affected significantly only one monitoring site in a short period of the day. Additionally this emission source decreased its impact in 2005. These findings indicate that only two monitoring sites are needed to characterize the observed PM₁₀ mass concentrations.

Keywords: Cluster analysis; Principal components analysis; Sulphur dioxide; Particulate matter

Management of air quality monitoring using principal component and cluster analysis—Part II: CO, NO₂ and O₃ by J.C.M. Pires; S.I.V. Sousa; M.C. Pereira; M.C.M. Alvim-Ferraz; F.G. Martins (pp. 1261-1274).

The aim of this study was to evaluate the performance of two statistical methods, principal component analysis (PCA) and cluster analysis (CA), for the management of air quality monitoring network (AQMN) of Oporto Metropolitan Area (Oporto-MA). The specific objectives were: (i) to identify city areas with similar air pollution behaviours; and (ii) to locate emission sources. The statistical methods were applied to the mass concentrations of carbon monoxide (CO), nitrogen dioxide (NO₂) and ozone (O₃), collected in the AQMN of Oporto-MA from January 2003 to December 2005.It was demonstrated that for each pollutant the monitoring sites are grouped into different classes based on their air pollution behaviour. The sites were divided: (i) into three different groups for CO and for NO₂ and (ii) into two groups for O₃. It was also found that several monitoring sites covered city areas characterized by the same specific air pollution behaviour, suggesting then an ineffective management of the air quality-monitoring system. The redundant equipment should be transferred to other monitoring sites allowing enlargement of the monitored area. The conclusions obtained with the statistical methods were supported by the location of main emission sources through the analysis of the wind direction. Four main emission sources of CO and NO₂ were located. Additionally, it was concluded that the sea wind had an important contribution towards the increase in the O₃ concentration. For all pollutants, two sites were always coupled in one group due to the different air pollution behaviour presented in the analysed period.

Keywords: Cluster analysis; Principal component analysis; Ozone; Carbon monoxide; Nitrogen dioxide

Observable indicators of the sensitivity of PM_2.5 nitrate to emission reductions—Part I: Derivation of the adjusted gas ratio and applicability at regulatory-relevant time scales by Robert W. Pinder; Robin L. Dennis; Prakash V. Bhave (pp. 1275-1286).

Chemical transport models have frequently been used to evaluate the impacts of emission reductions on inorganic PM_2.5. However, such models are limited in their accuracy by uncertain estimates of the spatial and temporal characterization of emissions and meteorology. Site-specific observations can more accurately characterize the distribution of pollutants, but cannot predict the effectiveness of emission controls. In this research, we use equilibrium theory and a chemical transport model to find observable indicators that are robust predictors of the change in PM_2.5 nitrate due to changes in NH₃, SO₂, and NO _x emissions. Two conditions are necessary: (1) the indicator must be valid at both instantaneous equilibrium and regulatory (daily and monthly) time-scales and (2) the indicator must be able to explain the majority of the spatial and temporal variance in the PM_2.5 nitrate sensitivity. We find that the ratio of free ammonia to total nitrate meets these conditions during the winter in the Eastern United States. This observable ratio can be used to predict the percent change in PM_2.5 nitrate due to SO₂ and NH₃ emissions reductions with nearly zero bias when compared with an emission driven chemical transport model. This permits a novel method for estimating the effectiveness of emission control strategies. The chemical transport model can be used to derive the relationship between the observed concentrations and the change in nitrate due to emission changes. Then observations can be used to apply that relationship to specific locations of interest.

Keywords: Inorganic aerosol system; Particulate matter; Air-quality modeling; Impacts of emission reductions

Observable indicators of the sensitivity of PM_2.5 nitrate to emission reductions—Part II: Sensitivity to errors in total ammonia and total nitrate of the CMAQ-predicted non-linear effect of SO₂ emission reductions by Robin L. Dennis; Prakash V. Bhave; Robert W. Pinder (pp. 1287-1300).

The inorganic aerosol system of sulfate, nitrate, and ammonium can respond non-linearly to changes in precursor sulfur dioxide (SO₂) emissions. The potential increase in nitrate, when sulfate is reduced and the associated ammonia is released, can negate the sulfate mass reduction. Current regional-scale air quality models do not reproduce the present-day levels of total ammonia and total nitrate, leading to possible errors in the air quality model predictions of future nitrate concentrations. The objective of this study is to quantify the effects of errors in the total-ammonia and total-nitrate budgets on nitrate relative response (RR), defined as the percent change in particulate nitrate stemming from reductions in SO₂ emissions. This objective is addressed through three sensitivity studies using the Community Multiscale Air Quality model (CMAQ). These studies assess the sensitivity of the nitrate RR (%) to (1) errors in ammonia emissions, (2) errors in the heterogeneous production of nitrate from N₂O₅, and (3) errors in the NO _X emissions. The results indicate that nitrate RRs due to SO₂ emission reductions are much more sensitive to errors in the total-ammonia budget than to errors in the total-nitrate budget. The sensitivity of the nitrate RR to NO _X emissions is only moderate and is due primarily to the effect of NO _X changes on sulfate production, rather than on total nitrate. Also, a strong relationship was found between the nitrate RR and the Adjusted Gas Ratio (free ammonia adjusted for the degree of sulfate neutralization divided by total nitrate).

Keywords: Inorganic aerosols; Sensitivity analysis; Non-linearity; Particulate nitrate replacement; Emission control response; Nitrate relative reduction factors; RRF

Temporal patterns of metal deposition at various scales in Austria during the last two decades by Harald G. Zechmeister; Daniela Hohenwallner; Andrea Hanus-Illnar; Harald Hagendorfer; Ingrid Roder; Alarich Riss (pp. 1301-1309).

Austria has been participating in the “European Moss Survey” within the UN-ECE ICP-vegetation since 1991. Three consecutive sampling periods in 1995, 2000 and 2005 were performed. Five moss species at 220 sampling sites (2.5 sites1000km⁻²) were analysed for Al, As, Cd, Co, Cr, Cu, Fe, Hg, Ni, Mo, Pb, V, and Zn concentrations. According to the retrospective analysis by 3-year-old moss segments, this investigation covered deposition in the period between 1989 and 2005. A relocation of sampling sites (within 2km²) was necessary for <10% of the sites within the overall period. On an Austria-wide scale all metals with the exception of Co, Cd and Hg showed a significant decrease of concentrations in the observed period. On a regional or site scale a large deviation from this general trend could be found, leading to significant differences between regions for many elements (e.g. for Co, Pb and Zn). Even continuous increases of metal deposition could be found at several sites (e.g. for Mo and Cu). This implies that pollution levels at different scales should be looked at in a differentiated way even in times of generally decreasing metal deposition.

Keywords: Biomonitoring; Moss; Heavy metals; Austria

Native and transplanted Pleurozium schreberi (Brid.)Mitt. as a bioindicator of N deposition in a heavily industrialized area of Upper Silesia (S Poland) by G. Kosior; A. Samecka-Cymerman; A. Chmielewski; R. Wierzchnicki; M. Derda; A.J. Kempers (pp. 1310-1318).

Over a period of 90 days, an assay was carried out with the moss Pleurozium schreberi transplanted from an uncontaminated control site to the most polluted industrialized region of Upper Silesia (centring around Katowice) in southern Poland. Within the same period, samples of native P. schreberi growing in the same industrialized region were collected, as well as P. schreberi from an unpolluted control site. The soils from the polluted sites contained high levels of N, and the concentrations of Pb and Zn in mosses also greatly exceeded those in plants from the unpolluted control sites. The deposition of atmospheric NH₄⁺ significantly exceeded that of airborne NO₃⁻ at all industrialized sites. The transplanted P. schreberi was a better nitrogen accumulator than the native moss in the less polluted parts of the area, showing a relation between the δ¹⁵N signature and tissue N concentration on the one hand and wet N deposition on the other after 45 and 90 days of exposure. P. schreberi transplanted into the more polluted sites of the industrialized area did not reach the level of nitrogen of the native species within 90 days of exposure and showed a relation to atmospheric N deposition only after 90 days of exposure. The transplants were thus poorer indicators of nitrogen deposition in heavily polluted areas than in less polluted regions. Transplanted P. schreberi was also a poorer indicator of nitrogen deposition in heavily polluted areas than native P. schreberi.

Keywords: Biomonitoring; Heavy metals (Pb; Zn); δ; ¹⁵; N signature; Coal industry; Pollution

Improvement of the Chemical Mass Balance model for apportioning—sources of non-methane hydrocarbons using composite aged source profiles by A.E.(Beth) Ann E. (Beth) Wittig; D.T. David T. Allen (pp. 1319-1337).

The Chemical Mass Balance (CMB) receptor model is commonly used to evaluate the relationship between emissions of air pollutants and their concentration in the ambient air. However, it is not clear that it can accurately achieve this goal when evaluating sources of reactive air pollutants such as non-methane hydrocarbons (NMHC).This work examines the ability of CMB Version 8.2 to accurately resolve sources of NMHC simulated for Houston, Texas, and assesses whether model performance can be improved by providing the model with composite aged profiles. The NMHC are simulated using an unsteady multi-stage photochemical transport model which uses reported emission rates from mobile and industrial sources and meteorological measurements as inputs. Composite aged profiles are also developed using the photochemical transport model, and account for the distribution and strength of sources within the common trajectories to the receptor. The ability of the model is examined through 128 cases and 4 case studies, which challenge CMB to resolve the sources of simulated NMHC when reasonable levels of uncertainty are introduced into the fitting species, source profiles, and/or sources provided to the model, or when composite aged source profiles are also made available to the model.CMB performs best when all contributing sources are known and perfect information is available to describe these sources. When reasonable uncertainties are introduced into any of its inputs, performance is poorer. Many cases do not result in a solution. In many of the cases that result in a solution, CMB fails to identify or attribute the mass of a relevant source to within ±30% of the true contribution, or identifies irrelevant sources and attributes to them more than 5% of the total mass. When composite aged profiles are made available to the model, inaccuracy is eliminated but many cases still do not result in a solution.

Keywords: Receptor model; Source apportionment; CMB; NMHC; Reactivity; Houston; Simulated data

Statistical correction and downscaling of chemical transport model ozone forecasts over Atlanta by Serge Guillas; Jinghui Bao; Yunsoo Choi; Yuhang Wang (pp. 1338-1348).

The Regional Air Quality forecAST (RAQAST) model is a regional chemical transport modeling system for ozone and its precursors over the United States. Since the grid size is 70 by 70km, forecasts cannot be made for a specific surface site. We use EPA monitoring stations from the Atlanta area to downscale and improve local forecasts using RAQAST outputs. We use the Model Diagnostic and Correction (MDC) approach. First, we regress the observations on the model outputs with an autoregressive noise component. Second, we regress the residuals of this first regression on variables associated with wind speed, precipitation amounts and the diurnal cycle. Deficiencies of 3-D model results are identified and corrected. Evaluation using measurements for a different period confirms that the statistically adjusted outputs reduce forecast errors by up to 25%.

Keywords: Surface ozone; Model evaluation; Statistical adjustment

Carbonyls emission from ethanol-blended gasoline and biodiesel-ethanol-diesel used in engines by Xiaobing Pang; Yujing Mu; Juan Yuan; Hong He (pp. 1349-1358).

Detailed carbonyls emissions from ethanol-blended gasoline (containing 10% v/v, ethanol, E-10) and biodiesel-ethanol-diesel (BE-diesel) were carefully investigated on an EQ491i gasoline engine equipped with a three-way-catalyst (TWC) and a Commins-4B diesel engine. In engine-out emissions for the gasoline engine, total carbonyls from E-10 varied in the range of 66.7–99.4mgkW⁻¹h⁻¹, which was 3.1–8.2% less than those from fossil gasoline (E-0). In tailpipe emissions, total carbonyls from E-10 varied in the range of 9.2–20.7mgkW⁻¹h⁻¹, which were 3.0–61.7% higher than those from E-0. The total carbonyls emissions from BE-diesel were 1–22% higher than those from diesel at different engine operating conditions. Compared with fossil fuels, E-10 can slightly reduce CO emission, and BE-diesel can substantially decrease PM emission, while both alternative fuels increased slightly NO _x emission.

Keywords: Carbonyls; Exhaust emissions; Ethanol-blended gasoline; Biodiesel

Within-urban variability in ambient air pollution: Comparison of estimation methods by Julian D. Marshall; Elizabeth Nethery; Michael Brauer (pp. 1359-1369).

An important component of air quality management and health risk assessment is improved understanding of spatial and temporal variability in pollutant concentrations. We compare, for Vancouver, Canada, three approaches for estimating within-urban spatiotemporal variability in ambient concentrations: spatial interpolation of monitoring data; an empirical/statistical model based on geographic analyses (“land-use regression”; LUR); and an Eulerian grid model (community multiscale air quality model, CMAQ). Four pollutants are considered—nitrogen oxide (NO), nitrogen dioxide (NO₂), carbon monoxide, and ozone—represent varying levels of spatiotemporal heterogeneity. Among the methods, differences in central tendencies (mean, median) and variability (standard deviation) are modest. LUR and CMAQ perform well in predicting concentrations at monitoring sites (average absolute bias: <50% for NO; <20% for NO₂). Monitors (LUR) offer the greatest (least) temporal resolution; LUR (monitors) offers the greatest (least) spatial resolution. Of note, the length scale of spatial variability is shorter for LUR (units: km; 0.3 for NO, 1 for NO₂) than for the other approaches (3–6 for NO, 4–6 for NO₂), indicating that the approaches offer different information about spatial attributes of air pollution. Results presented here suggest that for investigations incorporating spatiotemporal variability in ambient concentrations, the findings may depend on which estimation method is employed.

Keywords: Exposure analysis; Geographic information system (GIS); Traffic emissions; Land-use regression (LUR); Models-3/community multiscale air quality (CMAQ) model

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Atmospheric Environment (v.42, #6)