Atmospheric Environment (v.44, #24)
Editorial board (i).
Diurnal variability of total ozone column over Madrid (Spain) by M. Antón; M. López; A. Serrano; M. Bañón; J.A. García (2793-2798).
In recent years, research on ozone variability has mainly focused on the analysis of its trend. Additionally some studies have analyzed the annual, seasonal and day-to-day ozone variations. However, intra-diurnal total ozone variations are notably less explored. Thus, the main objective of this paper is to analyze the diurnal variability of total ozone column (TOC) as recorded by a Brewer spectrophotometer in Madrid (Spain). The results show that about 90% of days present non-negligible diurnal variability, indicating that, in general, it should not be assumed that TOC remains constant throughout a particular day in urban areas. In addition, this variability has a notable seasonal behavior which should be considered (the spring and summer months show higher diurnal TOC variations than autumn and winter months). This pattern is likely caused by the diurnal photochemical processes in the lower troposphere related to the formation of tropospheric ozone near the earth’s surface at populated urban locations. Thus, these diurnal fluctuations in tropospheric ozone could explain part of diurnal TOC variations (between 20% and 70% depending on the mixing layer height).
Keywords: Total ozone column; Tropospheric ozone; Diurnal variability; Brewer spectrophotometer;
WRF/Chem simulated springtime impact of rising Asian emissions on air quality over the U.S. by Yongxin Zhang; Seth C. Olsen; Manvendra K. Dubey (2799-2812).
This paper examines the impact of tripled anthropogenic emissions from China and India over the base level (gaseous species and carbonaceous aerosols for 2000) on air quality over the U.S. using the WRF/Chem (Weather Research and Forecasting – Chemistry) model at 1° resolution. WRF/Chem is a state-of-the-science, fully coupled chemistry and meteorology system suitable for simulating the transport and dispersion of pollutants and their impacts. The analyses in this work were focused on MAM (March, April and May). The simulations indicate an extensive area of elevated pollutant concentrations spanning from the Arabian Sea to the Northern Pacific and to the Northern Atlantic. MAM mean contributions from the tripled Asian emissions over the U.S. are found to be: 6–12 ppbv for CO, 1.0–2.5 ppbv for O3, and 0.6–1.6 μg m−3 for PM2.5 on a daily basis.
Keywords: Pollution from China and India; Regional impact; WRF/Chem;
Atmospheric phosphorus deposition at a montane site: Size distribution, effects of wildfire, and ecological implications by William C. Vicars; James O. Sickman; Paul J. Ziemann (2813-2821).
The dry deposition of atmospheric particulate matter can be a significant source of phosphorus (P) to oligotrophic aquatic ecosystems, including high-elevation lakes. In this study, measurements of the mass concentration and size distribution of aerosol particles and associated particulate P are reported for the southern Sierra Nevada, California, for the period July–October, 2008. Coarse and fine particle samples were collected with Stacked Filter Units and analyzed for Total P (TP) and inorganic P (IP) using a digestion-extraction procedure, with organic P (OP) calculated by difference. Particle size-resolved mass and TP distributions were determined concurrently using a MOUDI cascade impactor. Aerosol mass concentrations were significantly elevated at the study site, primarily due to transport from offsite and emissions from local and regional wildfires. Atmospheric TP concentrations ranged from 11 to 75 ng m−3 (mean = 37 ± 16 ng m−3), and were typically dominated by IP. Phosphorus was concentrated in the coarse (>1 μm diameter) particle fraction and was particularly enriched in the 1.0–3.2 μm size range, which accounted for 30–60% of the atmospheric TP load. Wildfire emissions varied widely in P content, and may be related to fire intensity. The estimated dry depositional flux of TP for each daily sampling period ranged between 7 and 118 μg m−2 d−1, with a mean value of 40 ± 27 μg m−2 d−1. Relative rates of dry deposition of N and P in the Sierra Nevada are consistent with increasing incidence of N limitation of phytoplankton growth and previously observed long-term eutrophication of lakes.
Keywords: Phosphorus; Atmospheric deposition; Forest fire; Eutrophication; Sierra Nevada;
Biomonitoring of air quality in the Cologne Conurbation using pine needles as a passive sampler – Part III: Major and trace elements by E. Lehndorff; L. Schwark (2822-2829).
We here report complementary trace element (Fe, Pb, Cd, Zn, Cr, Cu, Ni and sulfur) concentrations and ratios in pine needles collected in the urban area of Cologne, Germany. Potential element sources are discussed in conjunction with enviromagnetic and PAH data to evaluate air quality. Foliar trace element concentrations of Zn, Cr, Cu, Ni and sulfur are close to essential nutrient levels. Median concentrations of foliar Fe, Pb and Cd in Cologne are 132, 1.1, and 0.06 μg g−1, respectively. Thus these elements are enhanced over biogenic background levels and show significant accumulation with needle exposure time. Foliar sulfur concentrations vary between 868 and 2076 μg g−1 with a median value of 1409 μg g−1, except for two locations where 2370 and 2379 μg g−1 were observed. Cadmium serves as an indicator for local industrial emissions with short transport distances of only a few kilometres in Cologne City. Elevated Fe, Pb and Zn concentrations mark areas with higher traffic loads and agree with enhanced PAH burdens and magnetic susceptibility intensities of pine needles. Isopleths mapping and source differentiation of atmospheric pollutants using foliar trace elements is feasible. For temporal or spatial high-resolution studies more cost-effective environmental magnetics is recommended, which may guide in design of detailed studies aiming at identification and allocation of emission sources. Hereby, a combination of organic tracers (PAH), magnetic properties, and trace metals is considered most reliable.
Keywords: Pine needle; Sulfur; Biomonitoring; Passive sampler; Urban pollution;
Flow and contaminant transport in an airliner cabin induced by a moving body: Model experiments and CFD predictions by Stephane B. Poussou; Sagnik Mazumdar; Michael W. Plesniak; Paul E. Sojka; Qingyan Chen (2830-2839).
The effects of a moving human body on flow and contaminant transport inside an aircraft cabin were investigated. Experiments were performed in a one-tenth scale, water-based model. The flow field and contaminant transport were measured using the Particle Image Velocimetry (PIV) and Planar Laser-Induced Fluorescence (PLIF) techniques, respectively. Measurements were obtained with (ventilation case) and without (baseline case) the cabin environmental control system (ECS). The PIV measurements show strong intermittency in the instantaneous near-wake flow. A symmetric downwash flow was observed along the vertical centerline of the moving body in the baseline case. The evolution of this flow pattern is profoundly perturbed by the flow from the ECS. Furthermore, a contaminant originating from the moving body is observed to convect to higher vertical locations in the presence of ventilation. These experimental data were used to validate a Computational Fluid Dynamic (CFD) model. The CFD model can effectively capture the characteristic flow features and contaminant transport observed in the small-scale model.
Keywords: PIV; PLIF; CFD; Contaminant transport; Aircraft cabin; Ventilation; Human wake;
Chamber studies on mass-transfer of di(2-ethylhexyl)phthalate (DEHP) and di-n-butylphthalate (DnBP) from emission sources into house dust by Tobias Schripp; Christian Fauck; Tunga Salthammer (2840-2845).
For a number of phthalates and especially for di(2-ethylhexyl)phthalate (DEHP), surprisingly high house dust concentrations are reported in the literature. Therefore, the uptake of the most prominent compounds DEHP and di-n-butylphthalate (DnBP) from plasticized indoor materials into house dust samples of different organic content has been experimentally determined. The experiments have been performed within 45 days which is sufficient for the more volatile phthalate (DnBP) to reach equilibrium conditions. DnBP reaches considerably higher concentrations in the chamber air compared to real room measurements and, thus, also elevated dust concentrations. In contrast, the mass transfer of DEHP in the dust via the gas phase was significantly lower. However, small chamber experiments showed elevated mass transfer of DEHP in case of direct contact between emission source and sink. This aspect is experimentally determined using an plasticized PVC polymer with and without direct contact to house dust. A transfer into the dust could be observed in dependence of the initial concentration in the material. However, the results do not allow the differentiation between the two uptake mechanisms via capillary forces and contact to the material’s boundary layer. The results illustrate that the reasons for elevated DEHP concentrations in dust indoors can be traced back to direct contact of source and sink, abrasion from the source, and transport via airborne particles.
Keywords: Di-n-butylphthalate; Di(2-ethylhexyl)phthalate; House dust; Mass transfer;
Assimilation of conventional and satellite wind observations in a mesoscale atmospheric model for studying atmospheric dispersion by C.V. Srinivas; R. Venkatesan; V. Yesubabu; C. Nagaraju; K.M. Somayajai; P. Chellapandi; Baldev Raj (2846-2864).
A mesoscale atmospheric model PSU/NCAR MM5 is used to provide operational weather forecasts for a nuclear emergency response decision support system on the southeast coast of India. In this study the performance of the MM5 model with assimilation of conventional surface and upper-air observations along with satellite derived 2-d surface wind data from QuickSCAT sources is examined. Two numerical experiments with MM5 are conducted: one with static initialization using NCEP FNL data and second with dynamic initialization by assimilation of observations using four dimensional data assimilation (FDDA) analysis nudging for a pre-forecast period of 12 h. Dispersion simulations are conducted for a hypothetical source at Kalpakkam location with the HYSPLIT Lagrangian particle model using simulated wind field from the above experiments. The present paper brings out the differences in the atmospheric model predictions and the differences in dispersion model results from control and assimilation runs. An improvement is noted in the atmospheric fields from the assimilation experiment which has led to significant alteration in the trajectory positions, plume orientation and its distribution pattern. Sensitivity tests using different PBL and surface parameterizations indicated the simple first order closure schemes (Blackadar, MRF) coupled with the simple soil model have given better results for various atmospheric fields. The study illustrates the impact of the assimilation of the scatterometer wind and automated weather stations (AWS) observations on the meteorological model predictions and the dispersion results.
Keywords: Mesoscale; Assimilation; AWS; QuickSCAT; FDDA; Radiological dispersion;
Year-long continuous personal exposure to PM2.5 recorded by a fast responding portable nephelometer by Martin Braniš; Jana Kolomazníková (2865-2872).
Personal exposure to particulate matter of aerodynamic diameter under 2.5 μm (PM2.5) was monitored using a DustTrak nephelometer. The battery-operated unit, worn by an adult individual for a period of approximately one year, logged integrated average PM2.5 concentrations over 5 min intervals. A detailed time-activity diary was used to record the experimental subject’s movement and the microenvironments visited. Altogether 239 days covering all the months (except April) were available for the analysis. In total, 60 463 acceptable 5-min averages were obtained. The dataset was divided into 7 indoor and 4 outdoor microenvironments. Of the total time, 84% was spent indoors, 10.9% outdoors and 5.1% in transport. The indoor 5-min PM2.5 average was higher (55.7 μg m−3) than the outdoor value (49.8 μg m−3). The highest 5-min PM2.5 average concentration was detected in restaurant microenvironments (1103 μg m−3), the second highest 5-min average concentration was recorded in indoor spaces heated by stoves burning solid fuels (420 μg m−3). The lowest 5-min mean aerosol concentrations were detected outdoors in rural/natural environments (25 μg m−3) and indoors at the monitored person’s home (36 μg m−3). Outdoor and indoor concentrations of PM2.5 measured by the nephelometer at home and during movement in the vicinity of the experimental subject’s home were compared with those of the nearest fixed-site monitor of the national air quality monitoring network. The high correlation coefficient (0.78) between the personal and fixed-site monitor aerosol concentrations suggested that fixed-site monitor data can be used as proxies for personal exposure in residential and some other microenvironments. Collocated measurements with a reference method (β-attenuation) showed a non-linear systematic bias of the light-scattering method, limiting the use of direct concentration readings for exact exposure analysis.
Keywords: Air pollution; Particulate matter; Personal exposure; Microenvironment; Time-activity diary;
Influence of secondary formation on atmospheric occurrences of oxygenated polycyclic aromatic hydrocarbons in airborne particles by Yuki Kojima; Koji Inazu; Yoshiharu Hisamatsu; Hiroshi Okochi; Toshihide Baba; Toshio Nagoya (2873-2880).
Temporal and spatial variations in concentrations of particle-associated polycyclic aromatic hydrocarbons (PAHs) and their nitrated and oxygenated derivatives (nitro-PAHs and oxy-PAHs) were investigated to assess the influence of secondary formation on atmospheric occurrences of oxy-PAHs associated with particulate matter in downtown Tokyo, Japan. The daily variation in concentration of 1,8-naphthalic anhydride (1,8-NA) in summer 2007 was similar to that for 2-nitrofluoranthene (2-NF), a representative secondary formed nitro-PAH, while the variation for benzanthrone (BA) was similar to PAHs. In addition, the concentrations of polycyclic aromatic compounds (PACs) associated with airborne particulate matter decreased in the order of PAHs > BA > 9-fluorenone (9-FO) or 9,10-anthraquinone (9,10-AQ) > 1,8-NA with an increase in distance from the roadside, whereas 2-NF was constant. These results suggest that a considerable fraction of some oxy-PAHs such as 1,8-NA associated with airborne particulate matter in downtown Tokyo originates from atmospheric secondary formation.
Keywords: Oxy-PAHs; Nitro-PAHs; PAHs; Airborne particles; Tokyo;
Indoor particle size distributions in homes with open fires and improved Patsari cook stoves by Cynthia Armendáriz-Arnez; Rufus D. Edwards; Michael Johnson; Irma A. Rosas; F. Espinosa; Omar R. Masera (2881-2886).
Particulate pollution has been clearly linked with adverse health impacts from open fire cookstoves, and indoor air concentrations are frequently used as a proxy for exposures in health studies. Implicit are the assumptions that the size distributions for the open fire and improved stove are not significantly different, and that the relationship between indoor concentrations and personal exposures is the same between stoves. To evaluate the impact of these assumptions size distributions of particulate matter in indoor air were measured with the Sioutas cascade impactor in homes using open fires and improved Patsari stoves in a rural Purepecha community in Michoacan, Mexico. On average indoor concentrations of particles less than 0.25 μm were 72% reduced in homes with improved Patsari stoves, reflecting a reduced contribution of this size fraction to PM2.5 mass concentrations from 68% to 48%. As a result the mass median diameter of indoor PM2.5 particulate matter was increased by 29% with the Patsari improved stove compared to the open fire (from 0.42 μm to 0.59 μm, respectively). Personal PM2.5 exposure concentrations for women in homes using open fires were approximately 61% of indoor concentration levels (156 μg m−3 and 257 μg m−3 respectively). In contrast personal exposure concentrations were 77% times indoor air concentration levels for women in homes using improved Patsari stoves (78 μg m−3and 101 μg m−3 respectively). Thus, if indoor air concentrations are used in health and epidemiologic studies significant bias may result if the shift in size distribution and the change in relationship between indoor air concentrations and personal exposure concentrations are not accounted for between different stove types.
Keywords: Personal exposure; Indoor air; PM size distribution; Improved stoves; Mexico;
Survey of polyfluorinated chemicals (PFCs) in the atmosphere over the northeast Atlantic Ocean by Mahiba Shoeib; Penny Vlahos; Tom Harner; Andrew Peters; Margaret Graustein; Julie Narayan (2887-2893).
High volume air sampling in Bermuda, Sable Island (Nova Scotia) and along a cruise track from the Gulf of Mexico to northeast coast of the USA, was carried out to assess air concentrations, particle-gas partitioning and transport of polyfluorinated chemicals (PFCs) in this region. Samples were collected in the summer of 2007. Targeted compounds included the neutral PFCs: fluorotelomer alcohols (FTOHs), perfluoroalkyl sulfonamides (FOSAs) and perfluoroalkyl sulfonamido ethanols (FOSEs).Among the FTOHs, 8:2 FTOH was dominant in all samples. Sum of the concentration of FTOHs (gas+particle phase) were higher in Bermuda (mean, 34 pg m−3) compared to Sable Island (mean, 16 pg m−3). In cruise samples, sum of FTOHs were highly variable (mean, 81 pg m−3) reflecting contributions from land-based sources in the northeast USA with concentrations reaching as high as 156 pg m−3.Among the FOSAs and FOSEs, MeFOSE was dominant in all samples. In Bermuda, levels of MeFOSE were exceptionally high (mean, 62 pg m−3), exceeding the FTOHs. Sable Island samples also exhibited the dominance of MeFOSE but at a lower concentration (mean, 15 pg m−3). MeFOSE air concentrations (pg m−3) in cruise samples ranged from 1.6 to 73 and were not linked to land-based sources. In fact high concentrations of MeFOSE observed in Bermuda were associated with air masses that originated over the Atlantic Ocean.The partitioning to particles for 8:2 FTOH, 10:2 FTOH, MeFOSE and EtFOSE ranged from as high as 15 to 42% for cruise samples to 0.9 to 14% in Bermuda. This study provides key information for validating and developing partitioning and transport models for the PFCs.
Keywords: PFCs; Atmospheric transport; FTOHs; Perfluorooctanesulfonamide; Perfluorooctanesulfonamidoethanol;
Assessing multi-year changes in modeled and observed urban NOX concentrations from a dynamic model evaluation perspective by James M. Godowitch; George A. Pouliot; S. Trivikrama Rao (2894-2901).
An investigation of the concentrations of nitrogen oxides (NOX) from an air quality model and observations at monitoring sites was performed to assess the changes in NOX levels attributable to changes in mobile emissions. This evaluation effort focused on weekday morning rush hours since urban NOX concentrations are strongly influenced by the significant loading of emissions associated with heavy commuter traffic. On-road vehicle NOX emissions generated by the MOBILE6 model revealed a steady decline with an overall decrease of 25% for 2002–2006. In this study, a dynamic model evaluation was undertaken that entails an assessment of the predicted concentration response of the Community Multiscale Air Quality (CMAQ) model due to changes in NOX emissions as well as to meteorological variability spanning 3-month summer periods over five consecutive years (2002–2006) against observed concentration changes at NOX monitoring sites located primarily in urban areas of the eastern United States. Both modeled and observed hourly NOX concentrations exhibited maximum values that coincided with the morning peak NOX emissions. The notable results, based on 3-h average (6–9 AM local time) NOX concentrations, derived between the 50th and 95th percentiles of cumulative concentration distributions, revealed that modeled changes at these elevated NOX levels generally tracked the year-to-year variations in the observed concentration changes. When summer 2002 values were used as a reference, both modeled and observed results also showed definitive decreases in weekday morning urban NOX concentrations over this multi-year period, which can be primarily attributed to the reductions in mobile source emissions. Whereas observed NOX concentrations have declined by about 25% over this period consistent with the decline in the modeled mobile emission sector, modeled NOX concentration changes were close to the decreases exhibited in all (mobile + other sectors) surface NOX emissions whose overall decline was about 15% over this multi-year period.
Keywords: Dynamic model evaluation; Weekday NOX changes; Mobile NOX emissions; NOX concentrations; Air quality modeling;
Characterization of ambient PM2.5 concentrations by Tai-Yi Yu (2902-2912).
Statistical spatial and temporal analysis of PM2.5 concentrations in ambient air using principal component analysis may provide health risk information for air-quality management. This investigation simultaneously determines and interprets spatial variations and features of PM2.5 concentrations using ambient air-quality monitoring data during 2006–2008 and emission inventory. Daily mean values of PM2.5 and PM10 and maximum hourly data of SO2, CO, O3 and NO2 were calculated as sampling data for year 2006–2008. Therefore, principal component analysis and descriptive statistics of ambient air pollutants were utilized to assess the spatial features and variations of PM2.5 concentrations. This study also provides PM2.5/PM10 ratios and the rates at which 24-h particulate matter exceed air-quality standards over Taiwan. Analytical results indicate that four rotational components cumulatively explain 87% and 84% of concentration variances for PM10 and PM2.5 and form a delineation of four “influence regimes.” The separated districts of the four “influence regimes” for PM10 and PM2.5 were the same. With the rate at which PM2.5 24-h concentrations were above 65 μg m−3, 36% of air-quality stations, is higher than 10%; 24% of air-quality stations is higher than 15%. Based on analytical results, if the PM2.5 limit would be considered as National Ambient Air-Quality Standard in the future, the priority of reducing PM10 or O3 concentrations in the past decade could be replaced with PM2.5. The novel methodologies presented in this study can spatially assess adequate boundaries of atmospheric carrying capacity for particulate matter. Local governments located at the same influence regime characterized by factor loading isopleths should implement trans-boundary air pollution control programs. Box plots, the rates of particulate matter exceeding air-quality standards and PM2.5/PM10 ratios in distinct “influenced regimes” were also examined. Continued study of spatial and temporal variations in airborne PM2.5 concentrations will provide sufficient information about health risks and for air-quality control programs.
Keywords: Principal component analysis; Spatial variation; PM2.5; Taiwan;
Contribution of sugar-cane harvesting season to atmospheric contamination by polycyclic aromatic hydrocarbons (PAHs) in Araraquara city, Southeast Brazil by Sandro José de Andrade; Joyce Cristale; Flávio Soares Silva; Guilherme Julião Zocolo; Mary R.R. Marchi (2913-2919).
In Brazil, sugar-cane crops are burned to facilitate harvesting, and this causes environmental pollution from the large amounts of smoke and soot that are released into the atmosphere. The smoke and soot contain numerous organic compounds such as PAHs. In this study, PM10 and PAH concentrations in the air of Araraquara (SE Brazil, with around 200,000 inhabitants and surrounded by sugar-cane plantations) were determined during the harvest and non-harvest seasons. The sampling strategy included two campaigns in each season, with 20 samples per season. PM10 was collected using a Hi-vol sampler with Teflon™ – coated glass fiber filters. PM10 ranged from 41 to 181 μg m−3 during the harvest season, and from 12 to 47 μg m−3 during the non-harvest season. The mean total concentration of PAHs was 2.5 ng m−3 (non-harvest season) and 11.6 ng m−3 (harvest season). In all sampling periods, the most abundant polycyclic aromatic hydrocarbons were phenanthrene and fluoranthrene, and the least abundant was anthracene. The cluster analysis of the total PAH concentrations for each day of sampling and the corresponding meteorological data suggested that the atmospheric concentration of PAHs was independent of the differences in the weather between the seasons. For both sampling seasons, the statistical treatment (PCA, Varimax rotation and HCA) indicated the presence of vehicle sources (diesel, gasoline, and natural-gas engines); but for the harvest season, the main source was attributed to sugar-cane burning. The data generated by this study indicated the burning of sugar-cane as the main contributor to the high levels of PAHs detected in samples during the sugar-cane harvest season.
Keywords: Polycyclic aromatic hydrocarbons (PAHs); Sugar-cane; Biomass burning; Air pollution;
Short-term effect of increasing nitrogen deposition on CO2, CH4 and N2O fluxes in an alpine meadow on the Qinghai-Tibetan Plateau, China by Chunming Jiang; Guirui Yu; Huajun Fang; Guangmin Cao; Yingnian Li (2920-2926).
An increasing nitrogen deposition experiment (2 g N m−2 year−1) was initiated in an alpine meadow on the Qinghai-Tibetan Plateau in May 2007. The greenhouse gases (GHGs), including CO2, CH4 and N2O, was observed in the growing season (from May to September) of 2008 using static chamber and gas chromatography techniques. The CO2 emission and CH4 uptake rate showed a seasonal fluctuation, reaching the maximum in the middle of July. We found soil temperature and water-filled pore space (WFPS) were the dominant factors that controlled seasonal variation of CO2 and CH4 respectively and lacks of correlation between N2O fluxes and environmental variables. The temperature sensitivity (Q 10) of CO2 emission and CH4 uptake were relatively higher (3.79 for CO2, 3.29 for CH4) than that of warmer region ecosystems, indicating the increase of temperature in the future will exert great impacts on CO2 emission and CH4 uptake in the alpine meadow. In the entire growing season, nitrogen deposition tended to increase N2O emission, to reduce CH4 uptake and to decrease CO2 emission, and the differences caused by nitrogen deposition were all not significant (p < 0.05). However, we still found significant difference (p < 0.05) between the control and nitrogen deposition treatment at some observation dates for CH4 rather than for CO2 and N2O, implying CH4 is most susceptible in response to increased nitrogen availability among the three greenhouse gases. In addition, we found short-term nitrogen deposition treatment had very limited impacts on net global warming potential (GWP) of the three GHGs together in term of CO2-equivalents. Overall, the research suggests that longer study periods are needed to verify the cumulative effects of increasing nitrogen deposition on GHG fluxes in the alpine meadow.
Keywords: Anthropogenic nitrogen deposition; CO2; CH4; N2O; Q 10; Water-filled pore space; Alpine meadow; Qinghai-Tibetan plateau;
Evaluation of a CMAQ simulation at high resolution over the UK for the calendar year 2003 by C. Chemel; R.S. Sokhi; Y. Yu; G.D. Hayman; K.J. Vincent; A.J. Dore; Y.S. Tang; H.D. Prain; B.E.A. Fisher (2927-2939).
A comprehensive ‘operational’ evaluation of the performance of the Community Multiscale Air Quality (CMAQ) modelling system version 4.6 was conducted in support of pollution assessment in the UK for the calendar year 2003. The model was run on multiple grids using one-way nests down to a horizontal resolution as fine as 5 km over the whole of the UK. The model performance was evaluated for pollutants with standards and limit values (e.g. O3, PM10) and species contributing to acidic and nitrogenous deposition (e.g. NH3, SO4 2–, NO3 –, NH4 +) against data from operational national monitoring networks. The key performance characteristics of the modelling system were found to be variable according to acceptance criteria and to depend on the type (e.g. urban, rural) and location of the sites, as well as on the time of the year. As regards the techniques that were used for ‘operational’ evaluation, performance generally complied with expected levels and ranged from good (e.g. O3, SO4 2–) to moderate (e.g. PM10, NO3 –). At a few sites low correlations and large standard deviations for some species (e.g. SO2) suggest that these sites are subject to local factors (e.g. topography, emission sources) that are not well described in the model. Overall, the model tends to over predict O3 and under predict aerosol species (except SO4 2–). Discrepancies between predicted and observed concentrations may be due to a variety of intertwined factors, which include inaccuracies in meteorological predictions, chemical boundary conditions, temporal variability in emissions, and uncertainties in the treatment of gas and aerosol chemistry. Further work is thus required to investigate the respective contributions of such factors on the predicted concentrations.
Keywords: Air quality; Numerical simulation; Model performance; Evaluation;
New Directions: Passive control of personal air pollution exposure from traffic emissions in urban street canyons by Aonghus McNabola (2940-2941).