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Atmospheric Environment (v.44, #2)
Identification of brake wear particles and derivation of a quantitative tracer for brake dust at a major road by Johanna K. Gietl; Roy Lawrence; Alistair J. Thorpe; Roy M. Harrison (pp. 141-146).
Traffic-generated air pollutant emissions can be classified into exhaust and non-exhaust emissions. Increased attention is focussing on non-exhaust emissions as exhaust emissions are progressively limited by regulations. To characterise metal-rich emission from abrasion processes, size-segregated analysis of atmospheric aerosol particles sampled with micro-orifice uniform deposit impactors (MOUDI) in March 2007 in London was performed. The samples were collected at a roadside and a background site and were analysed for Al, Ba, Cu, Fe, Sb, Ti, V, Zn, Ca2+, K+, Mg2+, Na+, and NH4+. Most components showed a clear roadside increment, which was evident as a higher mass concentration and a change in the size distribution. In particular, Fe, Cu, Ba, and Sb correlated highly, indicative of a common traffic-related source. Using complementary information on the fleet composition, vehicle number and average speed, the brake wear emission was calculated using the EMEP/CORINAIR emission database. The total PM10 and barium emission of the traffic was determined by ratio to NOx whose source strength was estimated from published emission factors. Barium was found to comprise 1.1% of brake wear (PM10) particles from the traffic fleet as a whole, allowing its use as a quantitative tracer of brake wear emissions at other traffic-influenced sites.
Keywords: Brake wear; Size-segregated analysis; Trace metals; Urban roadside; Barium; London
Variability of ozone concentration in a montane environment, northern Italy by Elena Gottardini; Antonella Cristofori; Fabiana Cristofolini; Marco Ferretti (pp. 147-152).
To evaluate the spatial variability of ozone concentrations, two studies were undertaken in the montane environment of Trentino region, northern Italy, in 2007. In the first study, a 225 km2 area was considered. Here, a randomized design was used to evaluate the variability of ozone concentration at 1 and 225 km2 scale. Measurements were carried out by passive samplers between May and June 2007. In a second study, the whole 6207 km2 area of Trentino was considered. The area is covered by five grid cells of the European Monitoring and Evaluation Programme (EMEP). A systematic 15 × 15 km grid was used to allocate 15 passive samplers over the entire province, resulting into 1–4 samplers for each of the 5 EMEP grid cells (2500 km2 each) overlapping the study area. Measurements were carried out between June and September 2007. Accuracy of passive samplers was checked by direct comparison with conventional ozone analysers. Significant differences ( P = 0.034) were found in ozone concentration among 1 × 1 km quadrates within the 225 km2 study area, while variability within the 1 × 1 km grid cells (coefficient of variation, CV′ = 0.12) slightly exceed the measurement error (CV′ = 0.08). At larger scales (225, 2500 and 6207 km2), ozone concentration shows much higher variability (CV′ from 0.18 to 0.28, with peak values at 0.40). Reported differences lead to very different AOT40 estimates even within the same EMEP grid cell. These findings suggest that 1 × 1 km resolution seems appropriate for ozone concentration modelling. On the other hand, significant sub-grid variation may exist at the resolution adopted by the EMEP model. Coupled with the likely variability of other important meteorological, soil and vegetation variables, our findings suggest that ozone risk assessment for vegetation based on large-scale modelled AOT40 and flux needs to be considered with great caution. The evidence reported in this paper asks for more detailed national-scale modelling, and the development of methods to incorporate local scale variations into large-scale models.
Keywords: Ozone; AOT40; Large-scale models; Sub-grid variability
Impact of the Knudsen number and mass-transfer expression on multi-phase kinetic modeling by Prasad Pokkunuri; Paul Nissenson; Donald Dabdub (pp. 153-163).
Three different mass-transfer expressions are employed within the Model of Aerosol, Gas, and Interfacial Chemistry (MAGIC) to study gas-phase molecular chlorine and bromine production from NaCl and NaBr aerosols, respectively. Simulations of chamber experiments are performed in which NaCl aerosols react with gas-phase ozone in the presence of UV light, in order to identify the importance of the Knudsen number and mass-transfer expression in systems with varying contributions from gas-phase, aqueous-phase, and interfacial chemistry. In the case of NaBr aerosols, simulations are performed of both dark and photolytic conditions. A range of Knudsen numbers spanning the continuum, transition and free-molecular regimes is studied. Particle size is varied over three orders of magnitude, and particle concentration is changed to keep either (a) total aerosol volume or (b) total aerosol surface area constant. When total aerosol volume is constant, the total amount of surface area available for interfacial reaction increases linearly with Knudsen number. Consequently peak gas-phase Cl2 and Br2 concentrations increase by two orders of magnitude from the continuum regime to the free-molecular regime. When total aerosol surface area is constant, total aerosol volume is inversely proportional to Knudsen number, with lesser volume being available at higher Knudsen numbers. Consequently Cl− depletion in the kinetic regime leads to most gas-phase Cl2 being produced in the transition regime. Gas-phase Br2 concentration trends are determined by aqueous-phase reaction mechanisms, leading to a monotonic decrease in production with Knudsen number. At all Knudsen numbers, more gas-phase bromine is produced in the photolytic case than in the dark case, the difference being significant in the transition regime. Results of this study suggest that halogen production is insensitive to the mass-transfer expression used in the simulations.
Keywords: Knudsen number; Mass-transfer coefficient; Interfacial reaction; Multi-phase kinetics
A four-year size-segregated characterization study of particles PM10, PM2.5 and PM1 depending on air mass origin at Melpitz by G. Spindler; E. Brüggemann; T. Gnauk; A. Grüner; K. Müller; H. Herrmann (pp. 164-173).
PM10 measurements were started in November 1992 at Melpitz site. The mean PM10 concentration in 1993 was 38 μg m−3 in the summer season (May until October) and about 44 μg m−3 in the winter season (November until April). The mean PM10 level decreased until 1999 and varies now in ranges from 20–34 μg m−3 to 17–24 μg m−3 (minimum and maximum mean values for 1999–2008) in winter and summer seasons, respectively. High volume filter samples of particles PM10, PM2.5 and PM1 were characterized for mass, water-soluble ions, organic and elemental carbon from 2004 until 2008. The percentage of PM2.5 in PM10 varies between summer (71.6%) and winter seasons (81.9%). Mean concentrations of PM10, PM2.5 and PM1 in Melpitz were 20, 15, and 13 μg m−3 in 2004, 22, 18, and 13 μg m−3 in 2005, 24, 19, and 12 μg m−3 in 2006 and 22, 17, and 12 μg m−3 in 2007, respectively. In the four winters the rural background concentration PM10 at Melpitz exceeded the daily 50 μg m−3 limit for Europe on 8, 8, 7 and 6 days, respectively.Findings for a simple two-sector-classification of the samples (May 2004 until April 2008) using 96-h backward trajectories for the identification of source regions are: Air masses were transported most of time (60%) from the western sector and secondly (17%) from the eastern sector. The lowest daily mean mass concentration PM10 were found during western inflow in summer (17 μg m−3) containing low amounts of sulphate (2.4 μg m−3), nitrate (1.7 μg m−3), ammonium (1.1 μg m−3) and TC (3.7 μg m−3). In opposite the highest mean mass concentration PM10 was found during eastern inflow in winter (35 μg m−3) with high amounts of sulphate (6.1 μg m−3), nitrate (5.4 μg m−3), ammonium (3.8 μg m−3) and TC (9.4 μg m−3). An estimation of secondary formed OC (SOA) shows 0.8–0.9 μg m−3 for air masses from West and 2.1–2.2 μg m−3 from East. The seasonal difference can be neglected.The half-hourly measurements of the particle mass concentration PM10 evaluated as mean daily courses using a TEOM® show low values (14–21 μg m−3) in summer and winter for air masses transported from West and the highest concentrations (31–38 μg m−3) in winter for air masses from East.The results demonstrate the influence of meteorological parameters on long-range transport, secondary particle mass formation and re-emission which modify mass concentration and composition of PM10, PM2.5 and PM1. Melpitz site is located in the East of Germany faraway from strong local anthropogenic emissions (rural background). Therefore, this site is suitable for investigation of the influence of long-range transport of air pollution in continental air masses from the East with source regions inside and outside of the European Union.
Keywords: Particulate matter; Long-time measurements; Chemical–physical characterization; Long-range transport; Seasonal-spatial differentiation
Chemical and strontium isotope characterization of rainwater in karst virgin forest, Southwest China by Guilin Han; Yang Tang; Qixin Wu; Qiu Tan (pp. 174-181).
Strontium isotope ratios and concentrations of Ca2+, NH4+, Na+, K+, Mg2+, Cl−, SO42−, NO3− and Al3+, Sr2+ were measured for 52 rainwater samples collected in virgin forest in a rural region between May 2007 and Dec. 2008. The rainwater pH values vary from 4.1 to 7.2 with a volume weight mean (VWM) value of 5.40. 40 of 52 samples have pH value above 5.0, indicating that the regional rainwater was not acidic. Among anions and cations, sulphate concentration (40.4 μeq l−1, VWM) is the highest in the rainwater, followed by ammonium and calcium (30.2 and 20.8 μeq l−1, VWM). Rainwater quality is characterized by low salinity and neutralized pH.The chemical compositions and87Sr/86Sr ratios of the rainwater samples vary considerably. Using Na+ concentration as an indicator of marine origin, the proportions of sea salt and crustal elements were estimated from elemental ratios. The87Sr/86Sr ratios were used to characterize different sources base on the data sets of this study and those from literatures. Such sources include weathering of limestone (87Sr/86Sr = 0.7075), remote soil dust (87Sr/86Sr > 0.7135) and anthropogenic source (fertilizers:87Sr/86Sr = 0.7079). The results of the present study suggest that one likely source for high ammonium and calcium concentration is local soil. Due to a large contribution of these cations to the sulphate neutralization action, the rainwater in this region displays non-acidity, and thus has not significant environmental impact. The wet precipitation in the karst virgin forest in Guizhou province is strongly influenced by natural sources rather than anthropogenic sources.
Keywords: Major ions; Rainwater; Strontium isotopes; Karst virgin forest
Characteristics of springtime profiles and sources of ozone in the low troposphere over northern Taiwan by Chuan-Yao Lin; C.-C. Chang; C.Y. Chan; C.H. Kuo; W.-C. Chen; D. Allen Chu; Shaw C. Liu (pp. 182-193).
To quantify the possible sources of the high ambient ozone concentration in the low troposphere over Taiwan, ozone sounding data from a two-year intensive field measurement program conducted in April and early May of 2004 and 2005 in northern Taiwan has been examined. We found that the vertical ozone distributions and occurrence of enhanced ozone in the lower troposphere (below 6 km) mainly resulted from (1)Type NE: the long-range transport of ozone controlled by the prevailing northeasterly winds below 2 km, (2)Type LO: the local photochemical ozone production process, and (3)Type SW: the strong southwest/westerly winds aloft (2–6 km). In the boundary layer (BL), where Asian continental outflow prevails, the average profile for type NE is characterized by a peak ozone concentration of nearly 65 ppb at about 1500 m altitude. For type LO, high ozone concentration with an average ozone concentration greater than 80 ppb was also found in the BL in the case of stagnant atmospheric and sunny weather conditions dominated. For type SW, significant ozone enhancement with average ozone concentration of 70–85 ppb was found at around 4 km altitude. It is about 10 ppb greater than that of the types NE and LO at the same troposphere layer owing to the contribution of the biomass burning over Indochina. Due to Taiwan's unique geographic location, the complex interaction of these ozone features in the BL and aloft, especially features associated with northeasterly and south/southwesterly winds, have resulted in complex characteristics of ozone distributions in the lower troposphere over northern Taiwan.
Keywords: Ozone sounding; Low troposphere; Boundary layer
The influence of dynamic chamber design and operating parameters on calculated surface-to-air mercury fluxes by C.S. Eckley; M. Gustin; C.-J. Lin; X. Li; M.B. Miller (pp. 194-203).
Dynamic Flux Chambers (DFCs) are commonly applied for the measurement of non-point source mercury (Hg) emissions from a wide range of surfaces. A standard operating protocol and design for DFCs does not exist, and as a result there is a large diversity in methods described in the literature. Because natural and anthropogenic non-point sources are thought to contribute significantly to the atmosphere Hg pool, development of accurate fluxes during field campaigns is essential. The objective of this research was to determine how differences in chamber material, sample port placement, vertical cross sectional area/volume, and flushing flow rate influence the Hg flux from geologic materials. Hg fluxes measured with a Teflon chamber were higher than those obtained using a polycarbonate chamber, with differences related to light transmission and substrate type. Differences in sample port placement (side versus top) did not have an influence on Hg fluxes. When the same flushing flow rate was applied to two chambers of different volumes, higher fluxes were calculated for the chamber with the smaller volume. Conversely, when two chambers with different volumes were maintained at similar turnover times, the larger volume chamber yielded higher Hg fluxes. Overall, the flushing flow rate and associated chamber turnover time had the largest influence on Hg flux relative to the other parameters tested. Results from computational fluid dynamic (CFD) modeling inside a DFC confirm that the smaller diffusion resistance at higher flushing flows contributes to the higher measured flux. These results clearly illustrate that differences in chamber design and operation can significantly influence the resulting calculated Hg flux, and thus impact the comparability of results obtained using DFC designs and/or operating parameters. A protocol for determining a flushing flow rate that results in fluxes less affected by chamber operating conditions and design is proposed. Application of this protocol would provide a framework for comparison of data from different studies.
Keywords: Dynamic flux chamber; Atmosphere/surface exchange; Mercury; Flux; Emissions; Geologic materials
Tracer studies to characterize the effects of roadside noise barriers on near-road pollutant dispersion under varying atmospheric stability conditions by Dennis Finn; Kirk L. Clawson; Roger G. Carter; Jason D. Rich; Richard M. Eckman; Steven G. Perry; Vlad Isakov; David K. Heist (pp. 204-214).
A roadway toxics dispersion study was conducted at the Idaho National Laboratory (INL) to document the effects on concentrations of roadway emissions behind a roadside sound barrier in various conditions of atmospheric stability. The homogeneous fetch of the INL, controlled emission source, lack of other manmade or natural flow obstructions, and absence of vehicle-generated turbulence reduced the ambiguities in interpretation of the data. Roadway emissions were simulated by the release of an atmospheric tracer (SF6) from two 54 m long line sources, one for an experiment with a 90 m long noise barrier and one for a control experiment without a barrier. Simultaneous near-surface tracer concentration measurements were made with bag samplers on identical sampling grids downwind from the line sources. An array of six 3-d sonic anemometers was employed to measure the barrier-induced turbulence. Key findings of the study are: (1) the areal extent of higher concentrations and the absolute magnitudes of the concentrations both increased as atmospheric stability increased; (2) a concentration deficit developed in the wake zone of the barrier with respect to concentrations at the same relative locations on the control experiment at all atmospheric stabilities; (3) lateral dispersion was significantly greater on the barrier grid than the non-barrier grid; and (4) the barrier tended to trap high concentrations near the “roadway” (i.e. upwind of the barrier) in low wind speed conditions, especially in stable conditions.
Keywords: Wake zone; Traffic emissions; Pollutant dispersion near roadways; Concentration deficits
Particulate air quality model predictions using prognostic vs. diagnostic meteorology in central California by Jianlin Hu; Qi Ying; Jianjun Chen; Abdullah Mahmud; Zhan Zhao; Shu-Hua Chen; Michael J. Kleeman (pp. 215-226).
Comparisons were made between three sets of meteorological fields used to support air quality predictions for the California Regional Particulate Air Quality Study (CRPAQS) winter episode from December 15, 2000 to January 6, 2001. The first set of fields was interpolated from observations using an objective analysis method. The second set of fields was generated using the WRF prognostic model without data assimilation. The third set of fields was generated using the WRF prognostic model with the four-dimensional data assimilation (FDDA) technique. The UCD/CIT air quality model was applied with each set of meteorological fields to predict the concentrations of airborne particulate matter and gaseous species in central California. The results show that the WRF model without data assimilation over-predicts surface wind speed by ∼30% on average and consequently yields under-predictions for all PM and gaseous species except sulfate (S(VI)) and ozone(O3). The WRF model with FDDA improves the agreement between predicted and observed wind and temperature values and consequently yields improved predictions for all PM and gaseous species. Overall, diagnostic meteorological fields produced more accurate air quality predictions than either version of the WRF prognostic fields during this episode. Population-weighted average PM2.5 exposure is 40% higher using diagnostic meteorological fields compared to prognostic meteorological fields created without data assimilation. These results suggest diagnostic meteorological fields based on a dense measurement network are the preferred choice for air quality model studies during stagnant periods in locations with complex topography.
Keywords: Diagnostic meteorological fields; Prognostic meteorological fields; Data assimilation; UCD/CIT air quality model; California Regional Particulate Air Quality Study (CRPAQS)
Variation in biogenic volatile organic compound emission pattern of Fagus sylvatica L. due to aphid infection by É. Joó; H. Van Langenhove; M. Šimpraga; K. Steppe; C. Amelynck; N. Schoon; J.-F. Müller; J. Dewulf (pp. 227-234).
Volatile organic compounds (VOCs) have been the focus of interest to understand atmospheric processes and their consequences in formation of ozone or aerosol particles; therefore, VOCs contribute to climate change. In this study, biogenic VOCs (BVOCs) emitted from Fagus sylvatica L. trees were measured in a dynamic enclosure system. In total 18 compounds were identified: 11 monoterpenes (MT), an oxygenated MT, a homoterpene (C14H18), 3 sesquiterpenes (SQT), isoprene and methyl salicylate. The frequency distribution of the compounds was tested to determine a relation with the presence of the aphid Phyllaphis fagi L. It was found that linalool, (E)-β-ocimene, α-farnesene and a homoterpene identified as (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), were present in significantly more samples when infection was present on the trees. The observed emission spectrum from F. sylvatica L. shifted from MT to linalool, α-farnesene, (E)-β-ocimene and DMNT due to the aphid infection. Sabinene was quantitatively the most prevalent compound in both, non-infected and infected samples. In the presence of aphids α-farnesene and linalool became the second and third most important BVOC emitted. According to our investigation, the emission fingerprint is expected to be more complex than commonly presumed.
Keywords: Sesquiterpene; Methyl salicylate; Fagus sylvatica; L.; Phyllaphis fagi; L.; Emission change; Compound correlation; Monoterpene; VOC
Evaluation of airborne particulate matter and metals data in personal, indoor and outdoor environments using ED-XRF and ICP-MS and co-located duplicate samples by Jianjun Niu; Pat E. Rasmussen; Amanda Wheeler; Ron Williams; Marc Chénier (pp. 235-245).
Factors and sources affecting measurement uncertainty associated with monitoring metals in airborne particulate matter (PM) were investigated as part of the Windsor, Ontario Exposure Assessment Study (WOEAS). The assessment was made using co-located duplicate samples and a comparison of two analytical approaches: ED-XRF and ICP-MS. Sampling variability was estimated using relative percent difference (RPD) of co-located duplicate samples. The comparison of ICP-MS and ED-XRF results yields very good correlations ( R2 ≥ 0.7) for elements present at concentrations that pass both ICP-MS and ED-XRF detection limits (e.g. Fe, Mn, Zn, Pb and Cu). PM concentration ranges (median, sample number) of 24-h indoor PM10 and personal PM10 filters, and outdoor PM2.5 filters were determined to be 2.2–40.7 (11.0, n = 48) μg m−3, 8.0–48.3 (11.9, n = 48) μg m−3, and 17.1–42.3 (21.6, n = 18) μg m−3, respectively. The gravimetric analytical results reveal that the variations in PM mass measurements for same-day sampling are insignificant compared to temporal or spatial variations: 92%, 100% and 96% of indoor, outdoor and personal duplicate samples, respectively, pass the quality criteria (RPD ≤ 20%). Uncertainties associated with ED-XRF elemental measurements of S, Ca, Mn, Fe and Zn for 24-h filter samples are low: 78%–100% of the duplicate samples passed the quality criteria. In the case of 24-h filter samples using ICP-MS, more elements passed the quality criteria due to the lower detection limits. These were: Li, Na, K, Ca, Si, Al, V, Fe, Mn, Co, Cu, Mo, Ag, Zn, Pb, As, Mg, Sb, Sn, Sr, Th, Ti, Tl, and U. Low air concentrations of metals (near or below instrumental detection limits) and/or inadvertent introduction of metal contamination are the main causes for excluding elements based on the pass/fail criteria. Uncertainty associated with elemental measurements must be assessed on an element-by-element basis.
Keywords: Particulate matter; Uncertainty; Metals; Exposure assessment; Air pollution; ICP-MS; ED-XRF
A passive sampler for ambient gaseous oxidized mercury concentrations by Seth N. Lyman; Mae S. Gustin; Eric M. Prestbo (pp. 246-252).
This paper reports on the development of a passive sampler for estimating gaseous oxidized mercury concentrations. Atmospheric gaseous oxidized mercury concentrations calculated from passive sampler data were correlated with those obtained using an automated analyzer ( r2 = 0.71, p < 0.01, n = 110 for one-week deployments; r2 = 0.89, p < 0.01, n = 22 for two-week deployments). Sampler uptake was not significantly affected by changes in temperature, humidity, or ozone concentration, but it was slightly dependent on wind speed. As such, an equation for correcting data due to this factor was developed based on wind tunnel and field data. The detection limit for a two-week sampler deployment was ∼5 pg m−3. Field data collected in Nevada and the southeastern United States showed these samplers are useful for investigating spatial and temporal variability in gaseous oxidized mercury concentrations.
Keywords: Passive sampler; RGM; Gaseous oxidized mercury; Atmospheric; Monitoring
Measurements of ultrafine particles and other vehicular pollutants inside school buses in South Texas by Qunfang Zhang; Yifang Zhu (pp. 253-261).
Increasing evidence has demonstrated toxic effects of vehicular emitted ultrafine particles (UFPs, diameter < 100 nm), with the highest human exposure usually occurring on and near roadways. Children are particularly at risk due to immature respiratory systems and faster breathing rates. In this study, children’s exposure to in-cabin air pollutants, especially UFPs, was measured inside four diesel-powered school buses. Two 1990 and two 2006 model year diesel-powered school buses were selected to represent the age extremes of school buses in service. Each bus was driven on two routine bus runs to study school children’s exposure under different transportation conditions in South Texas. The number concentration and size distribution of UFPs, total particle number concentration, PM2.5, PM10, black carbon (BC), CO, and CO2 levels were monitored inside the buses. The average total particle number concentrations observed inside the school buses ranged from 7.3 × 103 to 3.4 × 104 particles cm−3, depending on engine age and window position. When the windows were closed, the in-cabin air pollutants were more likely due to the school buses’ self-pollution. The 1990 model year school buses demonstrated much higher air pollutant concentrations than the 2006 model year ones. When the windows were open, the majority of in-cabin air pollutants came from the outside roadway environment with similar pollutant levels observed regardless of engine ages. The highest average UFP concentration was observed at a bus transfer station where approximately 27 idling school buses were queued to load or unload students. Starting-up and idling generated higher air pollutant levels than the driving state. Higher in-cabin air pollutant concentrations were observed when more students were on board.
Keywords: School bus; Ultrafine particles; Engine age; Window position; In-cabin air quality
Use of CALPUFF for exposure assessment in a near-field, complex terrain setting by David L. MacIntosh; James H. Stewart; Theodore A. Myatt; Joseph E. Sabato; George C. Flowers; Kirk W. Brown; Dennis J. Hlinka; David A. Sullivan (pp. 262-270).
CALPUFF is an atmospheric source-receptor model recommended by the U.S. Environmental Protection Agency for use on a case-by-case basis in complex terrain and wind conditions. The ability of the model to provide useful information for exposure assessments in areas with those topographical and meteorological conditions has received little attention. This is an important knowledge gap for use of CALPUFF outside of regulatory applications, such as exposure analyses conducted in support of risk assessments and health studies. We compared deposition of cadmium (Cd), lead (Pb), and zinc (Zn) calculated with CALPUFF as a result of emissions from a zinc smelter with corresponding concentrations of the metals measured in attic dust and soil samples obtained from the surrounding area. On a point-by-point analysis, predictions from CALPUFF explained 11% (lead) to 53% (zinc) of the variability in concentrations measured in attic dust. Levels of heavy metals in soil interpolated to 100 residential addresses from the distribution of concentrations measured in soil samples also agreed well with deposition predicted with CALPUFF: R2 of 0.46, 0.76, and 079 for Pb, Cd, and Zn, respectively. Community-average concentrations of Cd, Pb, and Zn measured in soil were significantly ( p < 0.0001) and strongly correlated ( R2 ranged from 0.77 to 0.98) with predicted deposition rates. These findings demonstrate that CALPUFF can provide reasonably accurate predictions of the patterns of long-term air pollutant deposition in the near-field associated with emissions from a discrete source in complex terrain. Because deposition estimates are calculated as a linear function of air concentrations, CALPUFF is expected to be reliable model for prediction of long-term average, near-field ambient air concentrations in complex terrain as well.
Keywords: CALPUFF; Deposition; Near-field; Exposure
Impact of the mixing boundary layer on the relationship between PM2.5 and aerosol optical thickness by Neda Boyouk; Jean-François Léon; Hervé Delbarre; T. Podvin; C. Deroo (pp. 271-277).
The purpose of this paper is to study the relationship between columnar aerosol optical thickness and ground-level aerosol mass. A set of Sun photometer, elastic backscattering lidar and TEOM measurements were acquired during April 2007 in Lille, France. The PM2.5 in the mixed boundary layer is estimated using the lidar signal, aerosol optical thickness, or columnar integrated Sun photometer size distribution and compared to the ground-level station measurements. The lidar signal recorded in the lowest level (240m) is well correlated to the PM2.5 ( R2=0.84). We also show that the correlation between AOT-derived and measured PM2.5 is significantly improved when considering the mixed boundary layer height derived from the lidar. The use of the Sun photometer aerosol fine fraction volume does not improve the correlation.
Keywords: Mass concentration; Aerosol optical thickness; Boundary layer; Lidar
Aircraft measurements of the vertical distribution of sulfur dioxide and aerosol scattering coefficient in China by Likun Xue; Aijun Ding; Jian Gao; Tao Wang; Wenxing Wang; Xuezhong Wang; Hengchi Lei; Dezhen Jin; Yanbin Qi (pp. 278-282).
Information on the vertical distribution of air pollution is important for understanding its sources and processes and validating satellite retrievals and chemical transport models. This paper reports the results of the measurements of sulfur dioxide (SO2) and aerosol scattering coefficient (Bsp) obtained from several aircraft campaigns during summer and autumn 2007 in the north-eastern (NE), north-western (NW), and central-eastern (CE) regions of China. Their vertical profiles over the three regions with contrasting emission characteristics and climates are compared. Very high concentrations/values of SO2 and Bsp (with a value of up to 51 ppbv and 950 Mm−1, respectively) were recorded in the lower planetary boundary layer in CE China, indicating high SO2 emissions in the region. The SO2 column concentrations determined from the in-situ measurements were compared with Ozone Monitoring Instrument (OMI) SO2 retrievals. The results show that the OMI data could distinguish the varying levels of SO2 pollution in the study regions, but appeared to have underestimated the SO2 column in the highly polluted region of CE China.
Keywords: Aircraft observation; Vertical profile; SO; 2; PBL; OMI retrieval