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Atmospheric Environment (v.42, #8)
Exploring variability in pedestrian exposure to fine particulates (PM2.5) along a busy road by Stephen Greaves; Tharit Issarayangyun; Qian Liu (pp. 1665-1676).
In August 2006, pedestrian exposure to PM2.5 was monitored along a busy roadway in Sydney, Australia. The objective of the campaign was to assess the factors affecting exposure at both an inter- and intra-trip level. PM2.5 measurements were made at second-by-second intervals using a portable aerosol monitor, while simultaneously recording location with a personal GPS device. A digital voice recorder was used to record any events or circumstances, perceived to notably increase potential PM2.5 levels. The average PM2.5 concentration for the 39 trips conducted was 12.8μgm−3, which while 40% higher than concurrent ambient measurements was well within proposed daily standards for Australia. Multivariate time-series methods were then applied to study the effects of various interventions on PM2.5 at an intra-trip level while controlling for autocorrelation. Wind speed, traffic volumes and clearway operations (independent of traffic volumes) were found to be significant predictors in addition to the previous PM2.5 concentrations. Sensitivity analysis showed doubling traffic volumes increased PM2.5 concentrations by 26%, while each 5kmh−1 increase in wind speed increased PM2.5 concentrations by 10%. Several PM2.5 hotspots were identified where concentrations exceeded 100μgm−3. These were attributed to specific traffic (intersections, trucks, buses) and non-traffic sources (pedestrians smoking), typically only lasting a few seconds.
Keywords: Pedestrian exposure; PM; 2.5; Time-series methods; Personal monitoring; Sydney
Partitioning of major and trace components in PM10–PM2.5–PM1 at an urban site in Southern Europe by Perez N. Pérez; J. Pey; X. Querol; A. Alastuey; Lopez J.M. López; M. Viana (pp. 1677-1691).
Partitioning of major and trace components in PM10–PM2.5–PM1 at an urban site in Barcelona (Spain) in the Western Mediterranean was studied in the period 2005–2006. Particular attention was paid to the partitioning of mineral matter and to the evidence of possible interactions of mineral matter with other pollutants (gaseous pollutants and secondary PM). The results showed a high contribution of mineral matter (mainly anthropogenic, but sporadically associated with African dust outbreaks) in levels of both PM10 and PM2.5. A high proportion of nitrate was also present in the coarse fractions as a result of the interaction of mineral matter with gaseous pollutants. As at most urban sites in Europe, sulphate and carbonaceous aerosols are mainly present in the finer PM fractions. The PM1–2.5 fraction resembled that of PM10 in composition. The chemically unaccounted fraction (mostly bounded water) had also a fine grain size, probably because of the fine size of the hygroscopic aerosol components. The data series follow an increasing trend for PM1 levels (and less clearly for PM2.5) from 1999 to 2006, whereas no trend is observed for PM10.The contributions of African dust and regional soil resuspension to the annual PM10 levels has been estimated in around 1–2 and 2–3μgm−3 in this part of Spain. The African dust outbreaks accounted for around 15–20 exceedances of the European daily PM10 limit value.Finally, the data obtained were compared with data from selected European sites to highlight major differences in levels and speciation of PM.
Keywords: Atmospheric particulate matter; Speciation; Urban; Pollution; Mineral dust; Saharan dust
Characterization of polycyclic aromatic hydrocarbon emission from open burning of joss paper by J.-Y. Jui-Yeh Rau; H.-H. Hui-Hsin Tseng; M.-D. Min-Der Lin; M.-Y. Ming-Yen Wey; Y.-H. Yu-Hao Lin; C.-W. Chien-Wei Chu; C.-H. Ching-Hwa Lee (pp. 1692-1701).
The concentration of polycyclic aromatic hydrocarbons (PAHs) in the ambient air from a massive open burning of joss paper was simultaneously measured at an open-burning site (OS) and a downwind site (DS) from 6 to 8 August 2006. A total of 16 major PAHs (particle-bound and gas-phase) concentrations were extracted by the Soxhlet analytical method and analyzed by gas chromatography. The dominant PAHs of the total mass of the organic compound at both the sampling sites were low-molecular-weight species. Further, the results showed that the start burning/end burning-dominant PAH concentration ratios at the OS and DS were 10 and 6.2, respectively. Diagnostic ratios were also used in this study to characterize and identify the PAH emission sources. The results suggest that the characterization of air pollutants emitted from open-burning joss paper lies between furnace-burning joss paper and wood combustion.
Keywords: PAHs; Open burning; Joss paper; Suburban
An analysis of the spatial patterns of human health related surface ozone metrics across the UK in 1995, 2003 and 2005 by John R. Stedman; Andrew J. Kent (pp. 1702-1716).
Maps of a range of human health related surface ozone metrics for the UK have been generated using empirical measurements based models for the years 1995, 2003 and 2005. These years have been chosen to illustrate two recent years with higher and lower photochemical ozone contributions (2003 and 2005) and a year with higher photochemical ozone contributions combined with higher urban NO emissions (1995). A comparison of monitoring data with a transect of mapped values for London suggests that the empirically generated maps include a reasonably realistic description of the regional ozone concentrations and of the urban decrements of ozone concentrations.Estimates of the health impacts associated with ozone have been calculated from the mapped concentrations and are highly dependent on the metric chosen and thus on the implicit assumptions concerning the threshold concentration for effect (0, 70 or 100μgm−3). The year of maximum health impact is also dependent on the metric used. Estimated derived from the annual mean of the daily maximum of the running 8-h mean concentration with a cut-off of 0μgm−3 vary little from year-to-year, while the greatest impact was estimated to be in 1995 for annual mean of the daily maximum of the running 8-h mean concentration with a cut-off of 100μgm−3. Estimates derived from the annual mean of the daily maximum of the running 8-h mean concentration with a cut-off of 70μgm−3 were greatest in 2003, reflecting the fact that this metric (closely related to the SOMO35 metric adopted for European scale integrated assessment modelling) is influenced by both the magnitude of summer photochemical ozone episodes and the extent of titration with local NO emissions (the urban decrement). The models used should be applicable across much of NW Europe and other locations where there is little or no urban scale photochemical generation of ozone.
Keywords: Surface ozone; Empirical maps; Urban ozone; Health impact assessment
Experimental and numerical study on particle distribution in a two-zone chamber by Alvin C.K. Lai; K. Wang; F.Z. Chen (pp. 1717-1726).
Better understanding of aerosol dynamics is an important step for improving personal exposure assessments in indoor environments. Although the limitation of the assumptions in a well-mixed model is well known, there has been very little research reported in the published literature on the discrepancy of exposure assessments between numerical models which take account of gravitational effects and the well-mixed model.A new Eulerian-type drift-flux model has been developed to simulate particle dispersion and personal exposure in a two-zone geometry, which accounts for the drift velocity resulting from gravitational settling and diffusion.To validate the numerical model, a small-scale chamber was fabricated. The airflow characteristics and particle concentrations were measured by a phase Doppler Anemometer. Both simulated airflow and concentration profiles agree well with the experimental results. A strong inhomogeneous concentration was observed experimentally for 10μm aerosols.The computational model was further applied to study a simple hypothetical, yet more realistic scenario. The aim was to explore different levels of exposure predicted by the new model and the well-mixed model. Aerosols are initially uniformly distributed in one zone and subsequently transported and dispersed to an adjacent zone through an opening. Owing to the significant difference in the rates of transport and dispersion between aerosols and gases, inferred from the results, the well-mixed model tends to overpredict the concentration in the source zone, and under-predict the concentration in the exposed zone. The results are very useful to illustrate that the well-mixed assumption must be applied cautiously for exposure assessments as such an ideal condition may not be applied for coarse particles.
Keywords: Dispersion; Exposure; Eulerian model; Well-mixed model; Multi-zone
Origins of chemical pollution derived from Mid-Atlantic aircraft profiles using a clustering technique by Jennifer C. Hains; Brett F. Taubman; Anne M. Thompson; Jeffrey W. Stehr; Lackson T. Marufu; Bruce G. Doddridge; Russell R. Dickerson (pp. 1727-1741).
Upwind sources of NO x and SO2 play a crucial role in the amount of O3 and aerosols in the lower troposphere in the Mid-Atlantic US. This paper describes a novel method of clustering trace gas and aerosol profiles allowing for the quantification of the relationship between point sources and pollution levels. This improves our understanding of pollution origins and has the potential for prediction of episodes of poor air quality. A hierarchical clustering method was used to classify distinct chemical and meteorological events from over 200 aircraft vertical profiles in the lower troposphere. Profile measurements included O3, SO2, CO and particle scattering from June to August 1997–2003, in the Mid-Atlantic US (mostly in Maryland, Pennsylvania and Virginia). The clustering technique could discriminate distinct profile shapes including measurements made during the 2002 Canadian forest fires. Forty-eight-hour back trajectories were run for each profile and the integrated NO x and SO2 point source emissions encountered by each trajectory were calculated using data from the EPA Clean Air Market Division's emissions database. There was a strong correlation between integrated NO x emissions and O3 profiles, indicating that O3 profiles are strongly influenced by and can be predicted with point source emissions. There is a prevalent concentration of SO2 over the eastern US with mixing ratios decreasing smoothly from about 3.5ppb near the surface to 0.2ppb at 2400m.
Keywords: Ozone; SO; 2; Clustering; Emissions
Indoor and outdoor concentrations of organic and inorganic molecular markers: Source apportionment of PM2.5 using low-volume samples by David A. Olson; John Turlington; Rachelle M. Duvall; Stephen R. McDow; Carvin D. Stevens; Ron Williams (pp. 1742-1751).
Concentrations of PM2.5, elemental carbon (EC), organic carbon (OC), 30 organic source markers (13 alkanes, 14 polycyclic aromatic hydrocarbons and ketones, and 3 hopanes) and 19 inorganic source markers are reported from residential indoor, residential outdoor, and ambient microenvironments from a nine home pilot study conducted in Tampa, Florida. Mean daily PM2.5 concentrations were 9.3μgm−3 for residential indoor, 11.3μgm−3 for residential outdoor, and 12.7μgm−3 for ambient microenvironments. The EPA Chemical Mass Balance Model (CMB8.2) was used for source apportionment of PM2.5 residential outdoor samples. Four main sources of PM2.5 were identified: sulfate (55±6%) (average outdoor PM2.5±S.D.), gasoline-powered motor vehicles (32±4%), diesel-powered vehicles (8±2%), and road dust (5±1%).
Keywords: Organic source markers; Source apportionment; Exposure; Chemical Mass Balance (CMB)
Extinction spectra of mineral dust aerosol components in an environmental aerosol chamber: IR resonance studies by Praveen K. Mogili; K.H. Yang; Mark A. Young; Paul D. Kleiber; Vicki H. Grassian (pp. 1752-1761).
Mineral dust aerosol plays an important role in determining the physical and chemical equilibrium of the atmosphere. To better understand the impact that mineral dust aerosol may have on climate forcing and on remote sensing, we have initiated a study of the optical properties of important components of mineral dust aerosol including silicate clays (illite, kaolinite, and montmorillonite), quartz, anhydrite, and calcite. The extinction spectra are measured in an environmental simulation chamber over a broad wavelength range, which includes both the IR (650–5000cm−1) and UV–vis (12,500–40,000cm−1) spectral regions. In this paper, we focus on the IR region from 800 to 1500cm−1, where many of these mineral dust constituents have characteristic vibrational resonance features. Experimental spectra are compared with Mie theory simulations based on published mineral optical constants. We find that Mie theory generally does a poor job in fitting the IR resonance peak positions and band profiles for nonspherical aerosols in the accumulation mode size range ( D∼0.1–2.5μm). We explore particle shape effects on the IR resonance line profiles by considering analytic models for extinction of particles with characteristic shapes (i.e. disks, needles, and ellipsoids). Interestingly, Mie theory often appears to give more accurate results for the absorption line profiles of larger particles that fall in the coarse mode size range.
Keywords: Aerosol; Mineral dust; Mie theory; Remote sensing; Radiative forcing
The effect of salting with magnesium chloride on the concentration of particular matter in a road tunnel by Magne Aldrin; Ingrid Hobæk Haff; Pål Rosland (pp. 1762-1776).
This work presents an analysis of the effect of dust treatment with a magnesium chloride solution on the concentration of airborne particulate matter inside a road tunnel. During the winter 2004/2005, the road inside the tunnel of Strømsås was salted 43 times with magnesium chloride solution, of which 27 times with the amount20gm-2 and 16 with40gm-2. In addition, the road was swept 11 times and washed twice. Simultaneously, one recorded the concentration ofPM10 andPM2.5 hourly. The model used in the analysis is a generalised additive model (GAM) on log-scale, having traffic counts, diverse meteorological conditions and the pollution reducing actions as predictor variables.The analysis revealed no clear effect from sweeping and washing. The impact of the dust binding medium on the concentrations of particulate matter is, however, clearly propitious. As one would expect, it is largest immediately after applying the magnesium chloride, and diminishes steadily afterwards. The duration of the effect is estimated to 10 days, but with a rather large uncertainty (95% confidence intervals between 3 and 16 days). We estimated an effect (reduced pollution level) of70% on the concentration of the coarse particlesPM10–PM2.5 and56% on the concentration ofPM10. The estimated effect on the fine particlesPM2.5 is a modest17%, and barely significant.
Keywords: Air quality modelling; Urban air quality; Dust treatment; Road dust; Generalised additive models
Development of a computational system for estimating biogenic NMVOCs emissions based on GIS technology by Panagiotis Symeonidis; Anastasia Poupkou; Anthia Gkantou; Dimitrios Melas; Ozan Devrim Yay; Evangelia Pouspourika; Dimitrios Balis (pp. 1777-1789).
A computational system was developed that can be used for the compilation of spatially and temporally resolved biogenic non-methane volatile organic compounds emission inventories. A Geographic Information System was used to integrate a variety of input data including: satellite land use data, land-use specific emission potentials and foliar biomass densities, temperature and solar radiation data. The computational system was implemented focusing on the Balkan Peninsula and a biogenic isoprene, monoterpenes and other volatile organic compounds emission inventory was produced. The inventory has 1km spatial resolution and is driven by mean climatology. The annual total biogenic non-methane volatile organic compounds (NMVOCs) emissions over the study area are estimated to be 3769.2Gg, composed of 36.1% isoprene, 26.8% monoterpenes and 37.1% other volatile organic compounds (OVOCs). Approximately, 94% of annual isoprene emissions are produced from May to September, while this percentage is lower for monoterpenes and OVOCs (70% and 85%, respectively). Vegetation is a strong source of NMVOCs emissions in the study domain. On a country basis, for most of the countries studied, annual biogenic emissions represent a large share of the annual total NMVOCs emissions ranging from 70% to 80%.
Keywords: Biogenic emissions; NMVOCs; Emission inventory; GIS
The origin of black carbon on speleothems in tourist caves in South Korea: Chemical characterization and source discrimination by radiocarbon measurement by Sae Jung Chang; Gi Young Jeong; Soo Jin Kim (pp. 1790-1800).
Since the Gosu, Ondal, and Sungryu karst caves in South Korea became open to the public several decades ago, the surface of their speleothems has been turning black due to pollutants. The black pollutant is concentrated at the surface of speleothems, and the surface black layer is 0.1 to several millimeters thick. Elemental measurements of three bulk, acid-dissolved and oxidized fractions of the surface black layer show that the black pigment is a black carbon. The black carbon correlates positively with sulfates, nitrates, manganese, and lead, which are typical tracers of industrial and urban emissions. The14C-measurement of the black carbon, using accelerator mass spectrometry, shows that the black carbon was derived from both fossil-fuel combustion and biomass burning in roughly equal amounts, evidenced by fC value ranging from 0.340 to 0.592 (<±0.004, 1 σ). Therefore, protection of speleothems from black coloration requires control of anthropogenic black carbons carried by visitors. Suitable measures might include closure of caves, air cleaning of visitors and regulation of visitor numbers. The application of radiocarbon measurement of black carbon suggests that the fC is a valuable proxy for tracing the blackening phenomenon of natural and cultural heritage sites such as caves.
Keywords: Accelerator mass spectrometry; Black carbon; Cave; Radiocarbon; Speleothem
Polycyclic aromatic hydrocarbons (PAHs) in indoor dust matter of Palermo (Italy) area: Extraction, GC–MS analysis, distribution and sources by Maria Rosaria Mannino; Santino Orecchio (pp. 1801-1817).
Studies on indoor pollution are important since people spend more than 80% of their time indoor environments. In this work the method for PAHs analysis in indoor dust (used as passive sampler) and the results relative to samples collected in the area of Palermo are reported. Dust samples for analysis were collected from 45 indoor environments. Total PAHs concentrations in indoor dusts ranged from 36 to 34453μgkg−1d.w. To correlate indoor and outdoor pollution we analyze, also, the particulate matter and PAHs levels samples collected in four stations. The percentage measured in indoor dusts results more low than that found outside. The values of isomeric ratios for the different samples were used to individuate the predominant PAHs sources.
Keywords: Indoor; Dust; PAHs; GC–MS; Particulate
Mercury deposition in the Adirondacks: A comparison between precipitation and throughfall by H.-D. Hyun-Deok Choi; T.J. Timothy J. Sharac; T.M. Thomas M. Holsen (pp. 1818-1827).
The volume-weighted mean (VWM) Hg concentrations and the total cumulative fluxes in deciduous throughfall (6.6ngL−1 and 12.0μgm−2, respectively) were statistically higher than in precipitation (4.9ngL−1 and 11.6μgm−2, respectively) during 2 years of sampling at the Huntington Wildlife Forest in Newcomb, NY. Seasonally, the VWM Hg concentrations and the Hg fluxes in both precipitation and throughfall were lowest in winter and highest in summer. Due to the wash-off of dry deposition and foliar leaching, concentrations in throughfall were almost 50% higher than those in precipitation during the leaf-on period, while concentrations in throughfall were slightly higher than (or similar to) those in precipitation during the leaf-off period. During the 2 years of sampling, the total deposited cumulative flux in precipitation and deciduous throughfall were very similar (11.6μgHgm−2 and 12.0μgHgm−2, respectively), because the higher concentrations in throughfall were offset by smaller throughfall depths. Meteorological analysis indicated that the precipitation events resulting in the highest Hg fluxes were associated with trajectories that passed through regions of Midwest where major Hg sources including coal/oil-fired power plants and waste incinerators are located.
Keywords: Total mercury deposition; Throughfall; Precipitation; Meteorological analysis
Scientific uncertainties in atmospheric mercury models III: Boundary and initial conditions, model grid resolution, and Hg(II) reduction mechanism by Pruek Pongprueksa; C.J. Che-Jen Lin; Steve E. Lindberg; Carey Jang; Thomas Braverman; O. Russell Bullock Jr.; Thomas C. Ho; H.W. Hsing-Wei Chu (pp. 1828-1845).
In this study, the model response in terms of simulated mercury concentration and deposition to boundary condition (BC), initial condition (IC), model grid resolution (12km versus 36km), and two alternative Hg(II) reduction mechanisms, was investigated. The model response to the change of gaseous elemental mercury (GEM) concentration from 0 to 2ngm−3 in IC/BC is found to be very linear ( r2>0.99) based on the results of sensitivity simulations in July 2001. An increase of 1ngm−3 of GEM in BC resulted in an increase of 0.81ngm−3 in the monthly average of total mercury concentration, and 1270ngm−2 in the monthly total deposition. IC has similar but weaker effects compared to those of BC. An increase of 1ngm−3 of GEM in IC resulted in an increase of 0.14ngm−3 in the monthly average of total mercury concentration, and 250ngm−2 in the monthly total deposition. Varying reactive gaseous mercury (RGM) or particulate mercury (PHg) in BC/IC has much less significant impact. Simulation results at different grid resolutions show good agreement (slope=0.950–1.026, r=0.816–0.973) in mercury concentration, dry deposition, and total deposition. The agreement in wet deposition is somewhat weaker (slope=0.770–0.794, r=0.685–0.892) due to the difference in emission dilution and simulated precipitation that subsequently change reaction rates in the aqueous phase. Replacing the aqueous Hg(II)-HO2 reduction by either RGM reduction by CO (5×10−18cm3molecule−1s−1) or photoreduction of RGM (1×10−5s−1) gives significantly better model agreement with the wet deposition measured by Mercury Deposition Network (MDN). Possible ranges of the reduction rates are estimated based on model sensitivity results. The kinetic estimate requires further verification by laboratory studies.
Keywords: Atmospheric mercury; Boundary and initial conditions; CMAQ-Hg; Grid resolution; Mercury reduction mechanism
Air ion concentrations under overhead high-voltage transmission lines by E.R. Jayaratne; F.O. J-Fatokun; L. Morawska (pp. 1846-1856).
This paper reports net concentrations of small ions (NCSI) monitored at 41 sites under overhead high voltage ac power lines in and around an urban environment. The net ionic polarity under power lines was of both signs but mostly positive and NCSI varied widely from 0 to 3300cm−3. Concomitant measurements of the vertical dc electric field at the ground confirmed the presence of a net positive charge above. Approximately, 19% of the sites exhibited relatively high NCSI exceeding 1000cm−3. The mean value of all the sites was 776cm−3. Statistically, the mean for the transmission voltage (220–330kV) line sites was significantly higher than that for the sub-transmission voltage (110–132kV) line sites with means of 905 and 501cm−3, respectively. These values were compared with the mean urban outdoor concentration well away from the lines which was about 400cm−3 and of negative polarity. Overall, NCSI at approximately 76% of the power line sites exceeded the absolute mean urban outdoor value. The dc electric fields under the power lines showed a statistically significant relationship to the measured NCSI, although there was considerable scatter to indicate that electric field measurements do not necessarily reflect NCSI in the air at ground level.
Keywords: Atmospheric ions; Atmospheric electric field; Charged aerosols; Power lines
Global sensitivity analysis of a 3D street canyon model—Part I: The development of high dimensional model representations by T. Ziehn; A.S. Tomlin (pp. 1857-1873).
Traditional methods for global uncertainty and sensitivity analysis (SA) such as Monte Carlo methods based on full model simulations are often not suitable for application in environmental modelling due to the nonlinearity and computational complexity of the models. The high dimensional model representation (HDMR) method was developed to express the input–output relationships of a complex model with a high dimensional input space. HDMR provides a model replacement that can be easily employed within global SA. In this work an optimisation method is developed as an extension to the existing set of HDMR tools to improve the accuracy of the mapping process. An application from the field of urban flow and dispersion is chosen to demonstrate the effectiveness of the approach. Model replacements of a k–ε model simulating the flow field in an urban street canyon are constructed. The necessary computational effort for their construction is considerably lower than required by traditional global SA methods. First- and second-order sensitivity indices can then be calculated using the replacements without the need for additional full model runs. Comparison with a large sample of full model runs demonstrates that the output statistics of the full model are well represented by the model replacements. The proposed HDMR method therefore provides a powerful tool for general application to global SA of environmental models.
Keywords: Global sensitivity analysis; High dimensional model representation; Urban flow and dispersion; Street scale model; Street canyon
Global sensitivity analysis of a 3D street canyon model—Part II: Application and physical insight using sensitivity analysis by James Benson; Tilo Ziehn; Nick S. Dixon; Alison S. Tomlin (pp. 1874-1891).
In this work global sensitivity studies using Monte Carlo sampling and high dimensional model representations (HDMR) have been carried out on the k– ε closure computational fluid dynamic (CFD) model MISKAM, allowing detailed representation of the effects of changing input parameters on the model outputs. The scenario studied is that of a complex street canyon in the city of York, UK. The sensitivity of the turbulence and mean flow fields to the input parameters is detailed both at specific measurement points and in the associated canyon cross-section to aid comparison with field data. This analysis gives insight into how model parameters can influence the predicted outputs. It also shows the relative strength of each parameter in its influence. Four main input parameters are addressed. Three parameters are surface roughness lengths, determining the flow over a surface, and the fourth is the background wind direction. In order to determine the relative importance of each parameter, sensitivity indices are calculated for the canyon cross-section. The sensitivity of the flow structures in and above the canyon to each parameter is found to be very location dependant. In general, at a particular measurement point, it is the closest wall surface that is most influential on the model output. However, due to the complexity of the flow at different wind angles this is not always the case, for example when a re-circulating canyon flow pattern is present. The background wind direction is shown to be an important parameter as it determines the surface features encountered by the flow. The accuracy with which this is specified when modelling a full-scale situation is therefore an important consideration when considering model uncertainty. Overall, the uncertainty due to roughness lengths is small in comparison to the mean outputs, indicating that the model is well defined even with large ranges of input parameter uncertainty.
Keywords: Sensitivity analysis; Urban CFD model; Monte Carlo; HDMR; Street canyon
Aerosol climatology over four AERONET sites: An overview by H.D. Kambezidis; D.G. Kaskaoutis (pp. 1892-1906).
A 3-year data set from the AERONET sunphotometers is used to remotely sense the aerosol optical depth (AOD) and the Ångström wavelength exponent ( α) in four key locations characteristic of different environments. These sites are indicative of the dominance of different aerosol types, representing biomass burning, urban/industrial pollution, marine conditions and desert particles. The multiyear observations show robust differentiation in both values and spectral dependence of the AOD in the different environments. Higher AODs are depicted in tropical areas directly affected by forest fires, in urban areas due to heavy anthropogenic pollution as well as in desert regions under specific dust outbreaks. In contrast, remote oceanic regions can be characterized as areas without local pollution, where their aerosol load approaches background levels. In all locations, significant annual, seasonal and day-to-day variability in AOD and Ångström α is observed. The Ångström exponent exhibits its lowest values over oceanic and desert areas, ∼0.2–0.4, while it can reach 2.0, or even more, under intensive fire events. The seasonal variation of the AOD in biomass-burning areas shows a pronounced August–September peak, while in the other months the AOD is low. A clear seasonal pattern with maximum AOD in the period May–June is observed for the desert region, while the AOD's seasonal variation in urban and oceanic sites does not present a clear annual peak. As regards the Ångström exponent, a clear seasonal variation is depicted in the biomass-burning region with a peak in the burning season, and in desert areas with a minimum in the months with significant dust loading.
Keywords: Aerosol optical depth; Ångström exponent; Biomass burning; Urban/industrial; Clean maritime; Desert dust; AERONET
An evaluation of the wind erosion module in DUSTRAN by William J. Shaw; K. Jerry Allwine; Bradley G. Fritz; Frederick C. Rutz; Jeremy P. Rishel; Elaine G. Chapman (pp. 1907-1921).
Pacific Northwest National Laboratory (PNNL) has developed a dust transport model (DUSTRAN), which calculates atmospheric dust concentrations that result from both natural and human activity. DUSTRAN is a comprehensive dispersion modeling system, consisting of a dust-emissions module, a diagnostic meteorological model, and dispersion models that are integrated seamlessly into graphical information system (GIS) software. DUSTRAN functions as a console application and allows the user to interactively create a release scenario and run the underlying models.We have recently compared dust concentrations calculated by DUSTRAN with observations of wind erosion on the US Department of Energy's Hanford Site in southeastern Washington. In this paper we describe both DUSTRAN's algorithm for predicting the source strength of wind-blown dust and the comparison of simulated dust concentrations with data. The comparisons use observations of PM10 concentrations for three separate dust events on the Hanford Site in 2001. The dust measurements were made as part of an effort to monitor site recovery following a large range fire that occurred in 2000.The comparisons have provided both encouragement as to the practical value of the wind erosion module in DUSTRAN and examples of occasions when the simulations and observations diverge. In general, the maximum dust concentrations from the simulations and the observations for each dust event agreed closely. Because of the lack of soil moisture information, the model was run in a “dry” mode. However, certain discrepancies between the measured and simulated values relative to the timing of observed precipitation events suggest that soil moisture should be accounted for where possible. For low dust concentrations, DUSTRAN tends to overestimate PM10 levels. This may be a weakness in the form of the dust flux parameterization at low wind speeds. Overall, however, we have shown DUSTRAN to be an effective tool for simulating dust events due to wind erosion.
Keywords: Wind erosion; PM; 10; Dust flux; DUSTRAN; TEOM
Comparisons of modeled and observed isoprene concentrations in southeast Texas by Jihee Song; William Vizuete; Sunghye Chang; David Allen; Yosuke Kimura; Susan Kemball-Cook; Greg Yarwood; Marianthi-Anna Kioumourtzoglou; Elliot Atlas; Armin Hansel; Armin Wisthaler; Elena McDonald-Buller (pp. 1922-1940).
Biogenic emissions of hydrocarbons, primarily isoprene, dominate the VOC emission inventory in eastern Texas. Air quality model predictions of isoprene in southeast Texas were evaluated using ground and aircraft measurements collected during the Texas Air Quality Study 2000. The effects of two different vertical mixing schemes on model predictions of isoprene concentrations were also evaluated. The photochemical and biogenic emission estimation models used were the Comprehensive Air Quality Model with Extensions and the Global Biosphere Emissions and Interactions System. Ground level isoprene concentrations predicted by the models showed markedly good agreement with measured diurnal isoprene patterns. The vertical mixing schemes were most influential on surface concentrations, resulting in differences of as much as 270% in modeled isoprene concentrations. The model over predicted observations from airborne canister samples by as much as a factor of two over rural areas, but under predicted observations over urban areas. Modeled isoprene concentrations were also compared with measurements from an airborne Proton Transfer Reaction Mass Spectrometer, and the results indicated under prediction of isoprene by the model over urban areas, but better agreement in rural areas. The impacts of the vertical mixing schemes on isoprene concentrations were less direct aloft than at the surface. The resulting vertical redistribution of isoprene affected transport rates, chemistry, and the accumulation of mass. As a result, differences in concentrations aloft ranged from none to as much as 30%. This study reinforces the challenges of air quality model validation for highly reactive species such as isoprene, and the need for carefully controlled studies of biogenic emissions and chemical processing during different meteorological conditions in regions with spatially heterogeneous land use.
Keywords: Biogenic inventories; CAMx; GloBEIS inventory uncertainties; Isoprene
Tracers and impact of open burning of rice straw residues on PM in Eastern Spain by M. Viana; Lopez J.M. López; X. Querol; A. Alastuey; Garcia-Gacio D. García-Gacio; G. Blanco-Heras; Lopez-Mahia P. López-Mahía; Pineiro-Iglesias M. Piñeiro-Iglesias; M.J. Sanz; F. Sanz; X. Chi; W. Maenhaut (pp. 1941-1957).
Biomass burning emissions of rice straw residues may be carried out near urban agglomerations and may present a potential health risk for the population. Thus, tracers of these emissions should be clearly identified. We present a detailed chemical characterisation, including inorganic and organic tracer species, of PM10 aerosol at a rural site located close to the urban agglomeration of Valencia (Eastern Spain) during the rice straw burning season in 2006. Our results show that open burning of rice field residues increased daily PM10 concentrations on a regional scale (approximately 17,400ha) by 10–15μgm−3 on average, with a maximum of 30μgm−3 on peak episodic days. PM10 levels during open burning events were especially enriched in oxalate, fluoranthene, C31 n-alkane, levoglucosan, K, water-soluble organic carbon (WSOC), oleic acid, Cl−, Na, NO3−, and V. High enrichments were also obtained for Zn, Pb, Cr, Cd, and Na, probably as a consequence of the bioaccumulation of trace metals in rice straw and the influence of sea spray and brackish waters on the crops. Anthropogenic contributions from lubricant oil residues, probably from agricultural machinery or nearby traffic emissions, were also detected in the levels of n-alkanes (C19). The high Carbon Preference Index (CPI; >3.5) obtained for n-alkanoic acids confirmed their mostly biogenic origin. Organic tracers were more sensitive than inorganic species to the influence of indirect (regional scale or long-range transported) biomass burning emissions. Source apportionment of the PM10 mass by means of PCA-MLRA showed that rice straw burning reached maximum contributions up to 40% of the PM10 mass during peak episodes.
Keywords: Agricultural biomass; Open fire; PM; 10; WSOC; Levoglucosan; Oxalate; Potassium; Chlorine; CPI