Atmospheric Environment (v.41, #29)
Editorial board (i).
Selection of an appropriate model to predict plume dispersion in coastal areas by Ok-Hyun Park; Min-Gwang Seok (6095-6101).
In order to suggest a new methodology for selecting an appropriate dispersion model, various statistical measures having respective characteristics and recommended value ranges were integrated to produce a new single index by using fuzzy inference where eight statistical measures for various model results, including fractional bias (FB), normalized mean square error (NMSE), geometric bias mean (MG), geometric bias variance (VG), within a factor of two (FAC2), index of agreement (IOA), unpaired accuracy of the peak concentration (UAPC), and mean relative error (MRE), were taken as premise part variables. The new methodology using a single index was applied to the prediction of ground-level SO2 concentration of 1-h average in coastal areas, where eight modeling combinations were organized with fumigation models, σy schemes for pre-fumigation, and modification schemes for σy during fumigation. As a result, the fumigation model of Lyons and Cole was found to have better predictability than the modified Gaussian model assuming that whole plume is immerged into the Thermal Internal Boundary Layer (TIBL). Again, a better scheme of σy (fumigation) was discerned. This approach, which employed the new integrated index, appears to be applicable to model evaluation or selection in various areas including complex coastal areas.
Keywords: Atmospheric dispersion model; Statistical measures; Fuzzy inference; Model selection; Coastal area;
Composition and mixing state of the urban background aerosol in the Rhein-Main area (Germany) by Barbara P. Vester; Martin Ebert; Eric B. Barnert; Johannes Schneider; Konrad Kandler; Lothar Schütz; Stephan Weinbruch (6102-6115).
Size-resolved aerosol particle samples in the size range 0.1–10 μm aerodynamic diameter were collected in the years 2003 and 2004 at an urban background station in Mainz, Germany. Size, morphology, chemical composition and mixing state of more than 5400 individual particles of 7 selected sampling days were analyzed in detail by scanning electron microscopy and energy-dispersive X-ray microanalysis. In addition, transmission electron microscopy, aerosol mass spectrometry and atomic force microscopy were applied to obtain detailed information about the mixing state of the particles. The fine particle fraction (diameter<1 μm) is always dominated by complex secondary aerosol particles (⩾90% by number) independent from air mass origin. These particles are complex internal mixtures of ammonium and sodium sulfates, nitrates, and organic material. Between 20% and 40% of the complex secondary aerosol particles contain soot inclusions. The composition of the coarse particle fraction (>1 μm diameter) is strongly dependant on air mass history with variable abundances of complex secondary aerosol particles, aged sea salt, silicates, silicate mixtures, calcium sulfates, calcium sulfate/carbonate mixtures, calcium nitrate/carbonate mixtures, biological particles, and external soot.The dominance of complex secondary aerosol particles shows that reduction of the precursor gases is a major goal for successful reduction strategies for PM10.
Keywords: Urban background aerosol; Secondary aerosol; Soot; Mixing state; Electron microscopy;
Simulation of aerosols and gas-phase species over Europe with the Polyphemus system: Part I—Model-to-data comparison for 2001 by K.N. Sartelet; E. Debry; K. Fahey; Y. Roustan; M. Tombette; B. Sportisse (6116-6131).
This paper aims at presenting a validation of multi-pollutants over Europe with a focus on aerosols. Chemistry-Transport Models are now used for forecast and emission reduction studies not only for gas-phase species but also for aerosols. Comprehensive model-to-data comparisons are therefore required. We present in this paper a preliminary validation study of the Polyphemus system applied over Europe for 2001. The aerosol model is the SIze REsolved Aerosol Model (SIREAM). It is a sectional model that describes the temporal evolution of the size/composition distribution of atmospheric particles containing a mix of black carbon, mineral dust, inorganic species, and primary and secondary organics. In addition to a brief model description, we present an overview of the model validation. A comprehensive set of model-to-data statistics is computed with observational data extracted from three European databases (the EMEP, AirBase and BDQA databases). Model performance criteria are verified for ozone and particulate matter (PM) and its inorganic components. Comparisons of correlations and root mean square errors with those generated by other models run over Europe for 2001 indicate a good performance of the Polyphemus system. Modifications of the system configuration and parameterizations may have a significant impact on error statistics, which may question the robustness of such models. Because large differences exist between databases, the robustness of model-to-data error statistics is also investigated.
Keywords: Aerosol; Monitoring network; Chemistry-Transport Model; Model performance criteria;
Impact of mass consistency errors for atmospheric dispersion by Bruno Sportisse; Denis Quélo; Vivien Mallet (6132-6142).
Atmospheric dispersion models are usually off-line coupled to mesoscale meteorological models. This may generate the loss of mass consistency, defined as the conservation of uniform mixing ratio. We investigate in this short paper the impact of the resulting mass consistency errors. Three methods based on the renormalization of density, on fluxes computed with mass mixing ratio and on the adjustment of the vertical velocity, respectively, are aimed at reducing the mass consistency errors. They are benchmarked and applied to two test cases: air quality modeling over Europe for summer 2001 (typical of reactive dispersion) and simulation of the Chernobyl accident (typical of passive dispersion). Our tests indicate the differences between the passive and the reactive cases. The investigation of the spatial patterns (especially of the vertical distribution) discriminates the method based on the adjustment of the vertical velocity. Indeed, this method suffers from the enhancement of the numerical diffusion (illustrated in the passive case) and from the modification of the escape flux (for ozone).
Keywords: Mass consistency; Atmospheric dispersion; Air quality modeling;
Bayesian hierarchical modeling of personal exposure to particulate matter by Sandra J. McBride; Ron W. Williams; John Creason (6143-6155).
In the US EPA's 1998 Baltimore Epidemiology-Exposure Panel Study, a group of 16 residents of a single building retirement community wore personal monitors recording personal fine particulate air pollution concentrations (PM2.5) for 27 days, while other monitors recorded concurrent apartment, central indoor, outdoor and ambient site PM2.5 concentrations. Using the Baltimore panel study data, we develop a Bayesian hierarchical model to characterize the relationship between personal exposure and concentrations of PM2.5 indoors and outdoors. Personal exposure is expressed as a linear combination of time spent in microenvironments and associated microenvironmental concentrations. The model incorporates all available monitoring data and accounts for missing data and sources of uncertainty such as measurement error and individual differences in exposure. We discuss the implications of using personal versus ambient PM2.5 measurements in characterization of personal exposure to PM2.5.
Keywords: Statistical model; Bayesian hierarchical model; Human exposure; Particulate matter; Air pollution;
Laboratory studies on the uptake of aromatic hydrocarbons by ice crystals during vapor depositional crystal growth by Elke Fries; Elena Starokozhev; Werner Haunold; Wolfgang Jaeschke; Subir K. Mitra; Stephan Borrmann; Martin U. Schmidt (6156-6166).
Uptake of aromatic hydrocarbons (AH) by ice crystals during vapor deposit growth was investigated in a walk-in cold chamber at temperatures of 242, 251, and 260 K, respectively. Ice crystals were grown from ambient air in the presence of gaseous AH namely: benzene (C6H6), toluene (methylbenzene, C7H8), the C8H10 isomers ethylbenzene, o-, m-, p-xylene (dimethylbenzenes), the C9H12 isomers n-propylbenzene, 4-ethyltoluene, 1,3,5-trimethylbenzene (1,3,5-TMB), 1,2,4-trimethylbenzene (1,2,4-TMB), 1,2,3-trimethylbenzene (1,2,3-TMB), and the C10H14 compound tert.-butylbenzene. Gas-phase concentrations calculated at 295 K were 10.3–20.8 μg m−3. Uptake of AH was detected by analyzing vapor deposited ice with a very sensitive method composed of solid-phase micro-extraction (SPME), followed by gas chromatography/mass spectrometry (GC/MS).Ice crystal size was lower than 1 cm. At water vapor extents of 5.8, 6.0 and 8.1 g m−3, ice crystal shape changed with decreasing temperatures from a column at a temperature of 260 K, to a plate at 251 K, and to a dendrite at 242 K. Experimentally observed ice growth rates were between 3.3 and 13.3×10−3 g s−1 m−2 and decreased at lower temperatures and lower value of water vapor concentration. Predicted growth rates were mostly slightly higher.Benzene, toluene, ethylbenzene, and xylenes (BTEX) were not detected in ice above their detection limits (DLs) of 25 pg gice −1 (toluene, ethylbenzene, xylenes) and 125 pg gice −1 (benzene) over the entire temperature range. Median concentrations of n-propylbenzene, 4-ethyltoluene, 1,3,5-TMB, tert.-butylbenzene, 1,2,4-TMB, and 1,2,3-TMB were between 4 and 176 pg gice −1 at gas concentrations of 10.3–10.7 μg m−3 calculated at 295 K. Uptake coefficients (K) defined as the product of concentration of AH in ice and density of ice related to the product of their concentration in the gas phase and ice mass varied between 0.40 and 10.23. K increased with decreasing temperatures. Values of Gibbs energy (ΔG) were between −4.5 and 2.4 kJ mol−1 and decreased as temperatures were lowered. From the uptake experiments, the uptake enthalpy (ΔH) could be determined between −70.6 and −33.9 kJ mol−1. The uptake entropy (ΔS) was between −281.3 and −126.8 J mol−1 K−1. Values of ΔH and ΔS were rather similar for 4-ethlytoluene, 1,3,5-TMB and tert.-butylbenzene, whereas 1,2,3-TMB showed much higher values.
Keywords: Aromatic hydrocarbons; Ice-phase precipitation; Crystal growth; Uptake;
A side-by-side comparison of filter-based PM2.5 measurements at a suburban site: A closure study by J.C. Hains; L.-W.A. Chen; B.F. Taubman; B.G. Doddridge; R.R. Dickerson (6167-6184).
Assessing the effects of air quality on public health and the environment requires reliable measurement of PM2.5 mass and its chemical components. This study seeks to evaluate PM2.5 measurements that are part of a newly established national network by comparing them with more versatile sampling systems. Experiments were carried out during 2002 at a suburban site in Maryland, United States, where two samplers from the US Environmental Protection Agency (US EPA) Speciation Trends Network: Met One Speciation Air Sampling System—STNS and Thermo Scientific Reference Ambient Air Sampler—STNR, two Desert Research Institute Sequential Filter Samplers—DRIF, and a continuous TEOM monitor (Thermo Scientific Tapered Element Oscillating Microbalance, 1400a) sampled air in parallel. These monitors differ not only in sampling configuration but also in protocol-specific laboratory analysis procedures. Measurements of PM2.5 mass and major contributing species (i.e., sulfate, ammonium, organic carbon, and total carbon) were well correlated among the different methods with r-values >0.8. Despite the good correlations, daily concentrations of PM2.5 mass and major contributing species were significantly different at the 95% confidence level from 5% to 100% of the time. Larger values of PM2.5 mass and individual species were generally reported from STNR and STNS. These differences can only be partially accounted for by known random errors. Variations in flow design, face velocity, and sampling artifacts possibly influenced the measurement of PM2.5 speciation and mass closure. Statistical tests indicate that the current uncertainty estimates used in the STN and DRI network may underestimate the actual uncertainty.
Keywords: Aerosol sampling; Chemical speciation; PM2.5; Comparison study; Filter sampling;
Photochemical model performance for PM2.5 sulfate, nitrate, ammonium, and precursor species SO2, HNO3, and NH3 at background monitor locations in the central and eastern United States by Kirk Baker; Peter Scheff (6185-6195).
Health studies have shown premature death is statistically associated with exposure to particulate matter <2.5 μm in diameter (PM2.5). The United States Environmental Protection Agency requires all States with PM2.5 non-attainment counties or with sources contributing to visibility impairment at Class I areas to submit an emissions control plan. These emission control plans will likely focus on reducing emissions of sulfur oxides and nitrogen oxides, which form two of the largest chemical components of PM2.5 in the eastern United States: ammonium sulfate and ammonium nitrate. Emission control strategies are simulated using three-dimensional Eulerian photochemical transport models.A monitor study was established using one urban (Detroit) and nine rural locations in the central and eastern United States to simultaneously measure PM2.5 sulfate ion (SO4 2−), nitrate ion (NO3 −), ammonium ion (NH4 +), and precursor species sulfur dioxide (SO2), nitric acid (HNO3), and ammonia (NH3). This monitor study provides a unique opportunity to assess how well the modeling system predicts the spatial and temporal variability of important precursor species and co-located PM2.5 ions, which is not well characterized in the central and eastern United States.The modeling system performs well at estimating the PM2.5 species, but does not perform quite as well for the precursor species. Ammonia is under-predicted in the coldest months, nitric acid tends to be over-predicted in the summer months, and sulfur dioxide appears to be systematically over-predicted. Several indicators of PM2.5 ammonium sulfate and ammonium nitrate formation and chemical composition are estimated with the ambient data and photochemical model output. PM2.5 sulfate ion is usually not fully neutralized to ammonium sulfate in ambient measurements and is usually fully neutralized in model estimates. The model and ambient estimates agree that the ammonia study monitors tend to be nitric acid limited for PM2.5 nitrate formation. Regulatory strategies in this part of the country should focus on reductions in NO X rather than ammonia to control PM2.5 ammonium nitrate.
Keywords: Photochemical model; Regional air quality; PM2.5; Ammonia; Nitric acid; Sulfur dioxide;
Validation of DNDC for 22 long-term N2O field emission measurements by Daan Beheydt; Pascal Boeckx; Steven Sleutel; Changsheng Li; Oswald Van Cleemput (6196-6211).
Twenty-two long-term measurements of direct N2O emissions from soils in an intensive agricultural area were used for the validation of the process-based DNDC model (version 8.3P). Model simulations were evaluated for temporal patterns of N2O, NH4 +, NO3 − and water-filled pore space (WFPS) and total N2O emissions. Several soil and crop input parameter adjustments to the model were evaluated but only the recalculation of the WFPS at wilting point and at field capacity, using pedotransfer functions, resulted in a clear improvement of the simulated variables (WFPS in all cases, N2O in some cases). Therefore, only this adjustment was made to DNDC 8.3P. This change, however, resulted for some cases (both cropland and grassland) in retardation of nitrate leaching and to a lesser extent of NH4 + to the deeper soil layers. The goodness of fit of the simulated temporal pattern of N2O varied considerably between sites. The total simulated N2O emissions from cropland showed a good agreement with the measurements, although there was a systematic overestimation of 7.4 kg N2O-N ha−1. Grassland soils, in contrast, gave a low agreement between total simulated and measured N2O losses. On the basis of all measured data a regional emission factor of 3.16 with a 95% confidence interval of −0.89 to 7.21 could be calculated. DNDC simulations resulted in an emission factor of 6.49 with a 95% confidence interval of 4.04–8.93. The overall outcome of the N2O emission measurements and DNDC simulations were compared with several empirical regression models, which may be applicable for a temperate climate system. All of the tested regression models showed reliable results up to a N2O emission of 10 kg N2O-N ha−1. Higher emissions, however, were systematically underestimated. Though DNDC both under- and overestimated specific sites, the general agreement, over the whole range between measurements and simulations of total N2O losses (simulations=0.82×meas.+6.2), was better than for the different regression models.
Keywords: Process-based model; Regression model; Nitrous oxide emission; Agriculture; Greenhouse gas;
Kinetics of acid-catalyzed aldol condensation reactions of aliphatic aldehydes by Mia T. Casale; Aviva R. Richman; Matthew J. Elrod; Rebecca M. Garland; Melinda R. Beaver; Margaret A. Tolbert (6212-6224).
Field observations of atmospheric aerosols have established that organic compounds compose a large fraction of the atmospheric aerosol mass. However, the physical/chemical pathway by which organic compounds are incorporated into atmospheric aerosols remains unclear. The potential role of acid-catalyzed reactions of organic compounds on acidic aerosols has been explored as a possible chemical pathway for the incorporation of organic material into aerosols. In the present study, ultraviolet–visible (UV–vis) spectroscopy was used to monitor the kinetics of formation of the products of the acid-catalyzed aldol condensation reaction of a range of aliphatic aldehydes (C2–C8). The experiments were carried out at various sulfuric acid concentrations and a range of temperatures in order to estimate the rate constants of such reactions on sulfuric acid aerosols under tropospheric conditions. The rate constants were generally found to decrease as the chain length of the aliphatic aldehyde increased (except for acetaldehyde, which had an unusually small rate constant), increase as a function of sulfuric acid concentration as predicted by excess acidity theory, and showed normal Arrhenius behavior as a function of temperature. While the kinetic data are generally consistent with previous laboratory reports of aldehyde reactivity in various sulfuric acid media, the aldol condensation reactions involving aliphatic aldehydes do not appear fast enough to be responsible for significant transfer of organic material into atmospheric aerosols.
Keywords: Troposphere; Organic aerosols; Acid-catalyzed reactions; Kinetics;
Water uptake characteristics of individual atmospheric particles having coatings by Trudi A. Semeniuk; Matthew E. Wise; Scot T. Martin; Lynn M. Russell; Peter R. Buseck (6225-6235).
We used an environmental transmission electron microscope to observe deliquescence and hygroscopic growth of atmospheric particles with hygroscopic coatings over the range 0–100% relative humidity (RH). The particles were collected from polluted and clean environments. Types included a sulfate-coated NaCl/silicate aggregate particle, a sulfate-coated sea-salt particle, and a Mg-rich, chloride-coated sea-salt particle. They all exhibited initial water uptake between 50% and 60% RH, although the first major morphological changes occurred at 70% RH. A deliquescence sphere, adjacent to the core particle, formed between 70% and 76% RH when deliquescence occurred or when the liquid phase was able to break out of the solid exterior coating. The deliquescence sphere grew to engulf the particle with increasing RH. Some particles developed a splatter zone associated with a particle coating. Efflorescence occurred over the range 49–44% RH. Our results indicate that some coated particles undergo a multi-step deliquescence process and that composition of the different phases within the coating affects deliquescence and hygroscopic growth below 76% RH. Above 76% RH, the dominant hygroscopic growth was due to water uptake by NaCl. Efflorescence of these particles also was strongly linked to NaCl, although the presence of other phases inhibited formation of a single NaCl crystal. Our results show that the observed coatings can both enhance particle solubility and lower the effective deliquescence RH of the particle. Thus, these coatings cause important phase and size changes for aerosol particles that could feed back into many other chemical and physical processes that contribute to radiative forcing within the atmosphere.
Keywords: Hygroscopic coatings; Deliquescence; Efflorescence; Individual particles; ETEM;
PM10, PM2.5 and PM1.0—Emissions from industrial plants—Results from measurement programmes in Germany by C. Ehrlich; G. Noll; W.-D. Kalkoff; G. Baumbach; A. Dreiseidler (6236-6254).
Emission measurement programmes were carried out at industrial plants in several regions of Germany to determine the fine dust in the waste gases; the PM10, PM2.5 and PM1.0 fractions were sampled using a cascade impactor technique. The installations tested included plants used for: combustion (brown coal, heavy fuel oil, wood), cement production, glass production, asphalt mixing, and processing plants for natural stones and sand, ceramics, metallurgy, chemical production, spray painting, wood processing/chip drying, poultry farming and waste treatment. In addition waste gas samples were taken from small-scale combustion units, like domestic stoves, firing lignite briquettes or wood.In total 303 individual measurement results were obtained during 106 different measurement campaigns. In the study it was found that in more than 70% of the individual emission measurement results from industrial plants and domestic stoves the PM10 portion amounted to more than 90% and the PM2.5 portion between 50% and 90% of the total PM (particulate matter) emission. For thermal industrial processes the PM1.0 portion constituted between 20% and 60% of the total PM emission.Typical particle size distributions for different processes were presented as cumulative frequency distributions and as frequency distributions. The particle size distributions determined for the different plant types show interesting similarities and differences depending on whether the processes are thermal, mechanical, chemical or mixed. Consequently, for the groups of plant investigated, a major finding of this study has been that the particle size distribution is a characteristic of the industrial process. Attempts to correlate particle size distributions of different plants to different gas cleaning technologies did not lead to usable results.
Keywords: PM10; PM2.5; PM1.0; Stationary source emission; Emission measurement; Fine particles; Cascade impactor; Particle size distribution;
Influence of a large steel complex on the spatial distribution of volatile polycyclic aromatic hydrocarbons (PAHs) determined by passive air sampling using membrane-enclosed copolymer (MECOP) by Sung-Deuk Choi; Song-Yee Baek; Yoon-Seok Chang (6255-6264).
Membrane-enclosed copolymer (MECOPs) samplers containing crystalline copolymers of ethylvinylbenzene-divinylbenzene in polyethylene membranes were used to assess the influence of a steel complex on the level and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) in ambient air. MECOPs were deployed at six sites in Pohang, Korea for 37 days (August 9, 2005–September 14, 2005). Fluorene, phenanthrene, anthracene, and fluoranthene were dominant PAHs with the highest contribution of phenanthrene (59%) to the total amount of vapor-phase PAHs. The spatial distribution of total PAHs in the vapor phase ranging from 76 to 1077 ng MECOP−1 and air dispersion modeling suggested that the steel complex was the major PAH source in Pohang. It was revealed that the major wind directions rather than the distance from the steel complex were a significant factor affecting the levels of PAHs at the sampling sites. Finally, we tried to convert MECOP concentrations (ng MECOP−1) to air concentrations (ng m−3) with the modified sampling rates (m3 day−1). This study demonstrates again that passive air samplers are useful tools for spatially resolved and time-integrated monitoring of semivolatile organic compounds (SOCs) in ambient air.
Keywords: Volatile PAHs; MECOP; Passive air sampling; Steel production;
Surface tension of aqueous solutions of water-soluble organic and inorganic compounds by R. Tuckermann (6265-6275).
Surface tension of pure and mixed aqueous solutions of both inorganic and organic species that are relevant in atmospheric droplets has been studied in a laboratory investigation. Following the Gibbsian theory of surfaces experimental data have been fitted by the Szyszkowski equation. As a function of the carbon-chain length trends in the maximum surface excess Γ max and the inverse surface activity β have been clearly identified for pure aqueous solutions of homologous series of n-alcohols and mono-carboxylic acids, while these parameters oscillate for the homologous series of di-carboxylic acids. For mixed aqueous solutions of water-soluble organic and inorganic compounds, e.g. cis-pinonic acid and sodium chloride, a further decrease in surface tension has been observed, which can be interpreted as an interaction between the inorganic and organic solutes and an enrichment of the surface-active organic compound in the surface layer. Taking this effect into account surface-tension data of real atmospheric samples become more plausible, especially when also slightly soluble or water-insoluble organic compounds having a high surface activity at low concentrations are considered.
Keywords: Surface tension; Atmospheric droplets; Water-soluble organic compounds; Inorganic salts; Szyszkowski equation;
Fine particulate source apportionment using data from the USEPA speciation trends network in Chicago, Illinois: Comparison of two source apportionment models by Michael J. Rizzo; Peter A. Scheff (6276-6288).
Data from two of the United States Environmental Protection Agency's speciation trends network fine particulate matter sites within Chicago, Illinois were analyzed using the chemical mass balance (CMB) and positive matrix factorization (PMF) models to determine source contributions to the ambient fine particulate concentrations. The results from the two models were compared to determine the similarities and differences in the source contributions. This included examining the differences in the magnitude of the individual source contributions as well as the correlation between the contribution values from the two methods. The results showed that both models predicted sulfates, nitrates and motor vehicles as the three highest fine particle contributors for the two sites accounting for approximately 80% of the total. The PMF model attributed a slightly greater amount of fine particulate to the road salt, steel and soil sources while vegetative burning contributed more in the CMB results. Correlations between the contribution results from the two models were high for sulfates, nitrates and road salt with very good correlations existing for motor vehicles and petroleum refineries. The predicted PMF profiles agreed well with measured source profiles for the major species associated with each source.
Keywords: Source apportionment; Positive matrix factorization; Chemical mass balance; PM 2.5 ; Speciation trends network (STN); Receptor modeling;
Aerosol radiative forcing over the Indo-Gangetic plains during major dust storms by Anup K. Prasad; Sachchidanand Singh; S.S. Chauhan; Manoj K. Srivastava; Ramesh P. Singh; Risal Singh (6289-6301).
Indo-Gangetic (IG) alluvial plains, one of the largest river basins in the world, suffers from the long range transport of mineral dust from the western arid and desert regions of Africa, Arabia and Rajasthan during the summer (pre-monsoon season, April–June). These dust storms influence the aerosol optical depth (AOD) across the IG plains. The Kanpur AERONET (Aerosol Robotic Network) station and Moderate Resolution Imaging Spectro-radiometer (MODIS) data show pronounced effect on the aerosol optical properties and aerosol size distribution during major dust storm events over the IG plains that have significant effect on the aerosol radiative forcing (ARF). The multi-band AOD, from AERONET and MODIS, show contrasting changes in wavelength dependency over dust affected regions. A time collocated (±30 min) validation of AERONET AOD with MODIS Terra (level 2 swath product) over Kanpur, at a common wavelength of 550 nm for the period 2001–2005 show moderate correlation (R 2∼0.6) during the summer season. The average surface forcing is found to change by −23 W m−2 during dust events and the top of the atmosphere (TOA) forcing change by −11 W m−2 as compared to the non-dusty clear-sky days. A strong correlation is found between AOD at 500 nm and the ARF. At surface, the correlation coefficient between AOD and ARF is found to be high (R 2=0.925) and is found to be moderate (R 2=0.628) at the TOA. The slope of the regression line gives the aerosol forcing efficiency at 500 nm of about −46±2.6 W m−2 and −17±2.5 W m−2 at the surface and the TOA, respectively. The ARF is found to increase with the advance of the dry season in conjunction with the gradual rise in AOD (at 500 nm) from April (0.4–0.5) to June (0.6–0.7) over the IG plains.
Keywords: Aerosols; Dust storms; Radiative forcing; Summer season; Indo-Gangetic plains;
Air quality modelling over Bogota, Colombia: Combined techniques to estimate and evaluate emission inventories by Erika Zárate; Luis Carlos Belalcázar; Alain Clappier; Veronica Manzi; Hubert Van den Bergh (6302-6318).
Two versions of the Emission Inventory (EI) are generated for the city of Bogota, Colombia. In the first version (EI-1), CORINAIR traffic emission factors (EFs) are used. In the second (EI-2), bulk traffic EFs calculated for the city, using in situ measurements and inverse modelling techniques at street level, are used. EI-2 traffic emissions are 5, 4 and 3 times bigger than the corresponding values in EI-1, for CO, PM 10 and NMVOCs, respectively. The main goal of this study consists in evaluating the two versions of the EI when introduced into a mesoscale air quality model. The AOT (accumulated exposure over a threshold) index is calculated for comparison between observed and simulated concentrations of primary pollutants. Simulated concentrations using EI-2 are closer to the observed values. This comparison allows us to extract some conclusions of the methodology used to calculate the EFs. Local factors like the driving behavior, the altitude, vehicle technology and an aged fleet cannot be totally included and corrected in the standard methodologies, and seem to be more important than obtaining very detailed and precise information on the classification of the fleet or driving speeds. Under financially limited and fast changing situations, as in the case of many developing countries, a simple methodology to estimate bulk traffic EFs and to evaluate the EI, is of utmost importance. The use of combined techniques such as in situ measurements to estimate bulk traffic EFs, and further evaluation of the inventories with numerical models, proved to be a useful tool for this purpose.
Keywords: Bogota; Emission inventory; Real-world emissions; Urban air pollution; Air quality management;