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Atmospheric Environment (v.41, #5)
Source apportionment of PM10 in six cities of northern China by Xiaohui Bi; Yinchang Feng; Jianhui Wu; Yuqiu Wang; Tan Zhu (pp. 903-912).
Ambient PM10 was sampled in six northern China cities (Urumqi, Yinchuan, Taiyuan, Anyang, Tianjin and Jinan) from December 1999 to July 2002, and analyzed for 16 chemical elements, two water-soluble ions, total carbon, and organic carbon. In addition, chemical source profiles consisting of the same particulate components were obtained from a number of naturally occurring geological sources (soil dust from exposed lands) and sources of atmospheric particulates resulting from human activities (resuspended dust, cement, coal combustion fly ash, vehicle exhaust, and secondary particles). Ambient and source data were used in a chemical mass balance (CMB) receptor model to determine the major source of PM10 in these six cities. Results of CMB modeling showed that the major source of ambient PM10 in all the cities was resuspended dust. Significant contributions from coal fly ash were also found in all six cities.
Keywords: Source apportionment; Particulate matter; Chemical mass balance; Cities of northern China
Recreational atmospheric pollution episodes: Inhalable metalliferous particles from firework displays by Teresa Moreno; Xavier Querol; A. Andrés Alastuey; Cruz Minguillon Mari Cruz Minguillón; Jorge Pey; Sergio Rodriguez; J. Vicente Miro José Vicente Miró; Carles Felis; Wes Gibbons (pp. 913-922).
The use of fireworks creates an unusual and distinctive anthropogenic atmospheric pollution event. We report on aerosol samples collected during Las Fallas in Valencia, a 6-day celebration famous for its firework displays, and add comparative data on firework- and bonfire-contaminated atmospheric aerosol samples collected from elsewhere in Spain (Barcelona, L’Alcora, and Borriana) and during the Guy Fawkes celebrations in London. Specific high-profile official firework events during Las Fallas included the afternoon Mascletà and the nightly aerial displays (especially in the climactic final 2 days of the fiesta) and were accompanied by pollution spikes in suspended particles, NO, SO2, and the creation and dispersal of an aerosol cloud enriched in a range of metallic elements. Notable metal aerosol concentration increases recorded during Las Fallas were potassium (from 500 to 5900ngm−3), aluminium (as Al2O3 from around 600 to 2200ngm−3), titanium (from 200 to 700ngm−3), magnesium (from 100 to 500ngm−3), lead (from 17 to 379ngm−3), barium (from 39 to 322ngm−3), strontium (from 3 to 112ngm−3), copper (from 12 to 71ngm−3), and antimony (from 1 to 52ngm−3). Firework-contaminated aerosols of similarly metalliferous composition were also identified at the other monitoring sites, although different sites show variations attributable to other sources such as bonfires and local industry. Unusual levels of the trace elements Ba, Sr and (to a lesser extent) Cu, always in proportions with Ba dominant, along with strongly enhanced K, Pb, and Sb, are identified as being particularly characteristic of firework aerosols. Although firework-related recreational pollution episodes are transient in nature, they are highly concentrated, contribute significantly to total annual metal emissions, and are on average fine enough to be easily inhaled and a health risk to susceptible individuals.
Keywords: Fireworks; Aerosols; Airborne metals; Pollution episodes.
Contribution of railway traffic to local PM10 concentrations in Switzerland by Robert Gehrig; Matz Hill; Peter Lienemann; Christoph N. Zwicky; Nicolas Bukowiecki; Ernest Weingartner; Urs Baltensperger; Brigitte Buchmann (pp. 923-933).
Field measurement campaigns of PM10 and its elemental composition (daily sampling on filters) covering different seasons were performed at two sites near the busiest railway station of Switzerland in Zurich (at a distance of 10m from the tracks) and at a site near a very busy railway line with more than 700 trains per day. At this latter site parallel samples were taken at 10, 36 and 120m distances from the tracks with the aim to study the distance dependence of the railway induced PM10 concentrations.To distinguish the relatively small railway emissions from the regional background (typically 20–25μgm−3), simultaneous samples were also taken at an urban background site in Zurich. The differences in PM10 and elemental concentrations between the railway exposed sites and the background site were allocated to the railway contribution.Small, however, measurable PM10 concentration differences were found at all sites. The elemental composition of these differences revealed iron as the only quantitatively important constituent. As a long-term average it amounted to approximately 1μgm−3 Fe at a distance of 10m from the tracks at all three sites. Assuming that iron was at least partly oxidised (e.g. in the form of Fe2O3) the contribution can amount up to 1.5μgm−3. Emissions of copper, manganese and chromium from trains were also clearly identified. However, compared to iron these, elements were emitted in very low quantities.No significant contribution from rock material (calcium, aluminium, magnesium, sodium) was observed as might have been expected from erosion, abrasion and resuspension from the gravel below the tracks. Particle emissions from diesel exhaust were not considered as trains in Switzerland are operated nearly exclusively by electric locomotives.The railway, induced contribution to ambient PM10 decreased rapidly with increasing distance from the tracks. At a distance of 120m this contribution dropped to only 25% of the contribution observed at 10m distance.
Keywords: Particulate matter; Railroad; Iron; Abrasion
Modeling reactive pollutant dispersion in an urban street canyon by J.-J. Jong-Jin Baik; Y.-S. Yoon-So Kang; J.-K. Jae-Jin Kim (pp. 934-949).
Reactive pollutant dispersion in an urban street canyon with a street aspect ratio of one is numerically investigated using a computational fluid dynamics (CFD) model. The CFD model developed is a Reynolds-averaged Navier–Stokes equations (RANS) model with the renormalization group (RNG) k–ε turbulence model and includes transport equations for NO, NO2, and O3 with simple photochemistry. An area emission source of NO and NO2 is considered in the presence of background O3 and street bottom heating (Δ T=5°C) with an ambient wind perpendicular to the along-canyon direction. A primary vortex is formed in the street canyon and the line connecting the centers of cross-sectional vortices meanders over time and in the canyon space. The cross-canyon-averaged temperature and reactive pollutant concentrations oscillate with a period of about 15min. The averaged temperature is found to be in phase with NO and NO2 concentrations but out of phase with O3 concentration. The photostationary state defect is small in the street canyon except for near the roof level and the upper downwind region of the canyon and its local minimum is observed near the center of the primary vortex. The budget analysis of NO (NO2) concentration shows that the magnitude of the advection or turbulent diffusion term is much larger (larger) than that of the chemical reaction term and that the advection term is largely balanced by the turbulent diffusion term. On the other hand, the budget analysis of O3 concentration shows that the magnitude of the chemical reaction term is comparable to that of the advection or turbulent diffusion term. The inhomogeneous temperature distribution itself affects O3 concentration to some extent due to the temperature-dependent photolysis rate and reaction rate constant.
Keywords: Computational fluid dynamics (CFD) model; Urban street canyon; Street bottom heating; Reactive pollutant dispersion; Photochemistry
An exceptional ozone episode in northern Fennoscandia by A. Lindskog; P.-E. Karlsson; P. Grennfelt; S. Solberg; C. Forster (pp. 950-958).
Ground-based observations of ozone have been performed at three sites in northern Fennoscandia, Karasjok, Esrange and Pallas. The sites are located in remote, unpolluted areas far away from the European source regions, and thus representing the northern hemispheric background. Events of photochemical episodes are rare. However, on 19 and 20 April 2003 two episodes with unusually high ozone values were measured at these stations. The highest values of 85.4 and 83.5ppbv were observed at Esrange and Pallas, respectively, on the 20th April. A simultaneous increase of other pollutants, e.g. nitrate, supports the idea that this was an anthropogenic episode to the far north. A third episode was seen on the 21st at Esrange and Pallas but not at Karasjok.Results from a source–receptor analysis with the particle dispersion model FLEXPART show southern continental Europe as the main source of the polluted air masses in connection with the enhanced ozone, whereas in between transport of cleaner air masses from the North-Atlantic took place. The highest ozone peaks measured at Esrange and Pallas can most likely be traced back to transport of pollution from the Iberian peninsula superimposed on pollution transported from the Northern Mediterranean.
Keywords: Ozone; Backward simulations; Source–receptor analysis; Flexpart; Long-range transport; Spatial variation
The effects of ozone/limonene reactions on indoor secondary organic aerosols by Golam Sarwar; Richard Corsi (pp. 959-973).
An indoor air quality model was used to predict dynamic particle mass concentrations based on homogeneous chemical mechanisms and partitioning of semi-volatile products to particles. The ozone–limonene reaction mechanism was combined with gas-phase chemistry of common atmospheric organic and inorganic compounds and incorporated into the indoor air quality model. Experiments were conducted in an environmental chamber to investigate secondary particle formation resulting from ozone/limonene reactions. Experimental results indicate that significant fine particle growth occurs due to the interaction of ozone and limonene and subsequent intermediate by-products. Secondary particle mass concentrations were estimated from the measured particle size distribution. Predicted particle mass concentrations were in good agreement with experimental results—generally within ∼25% at steady-state conditions. Both experimental and predicted results suggest that air exchange rate plays a significant role in determining secondary fine particle levels in indoor environments. Secondary particle mass concentrations are predicted to increase substantially with lower air exchange rates, an interesting result given a continuing trend toward more energy efficient buildings. Lower air exchange rates also shifted the particle size distribution toward larger particle diameters. Secondary particle mass concentrations are also predicted to increase with higher outdoor ozone concentrations, higher outdoor particle concentrations, higher indoor limonene emission rates, and lower indoor temperatures.
Keywords: Indoor chemistry; Ozone; Limonene; Terpenes; Secondary aerosols
Monitoring of atmospheric reduced sulfur compounds and their oxidation in two coastal landfill areas by S.-K. Sang-Keun Song; Z.-H. Zang-Ho Shon; K.-H. Ki-Hyun Kim; Seong Cheon Kim; Y.-K. Yoo-Keun Kim; J.-K. Jung-Kwon Kim (pp. 974-988).
In this study, the distribution characteristics of reduced sulfur compounds (RSCs) in ambient air were investigated in two coastal landfill (LF) facilities and their surrounding areas. The photochemical conversion of RSCs to sulfur dioxide (SO2) was also evaluated using a photochemical box model (PCBM). Measurements of RSCs were carried out from both in and around areas of two coastal LFs in Gunsan (G) and Donghae (D) city, Korea during several field campaigns (May through December 2004). The dominant RSCs at the Gunsan landfill (G-LF) were found to be DMS and H2S, whereas those at the Donghae landfill (D-LF) were H2S and DMDS. The concentrations of DMS at these study sites were likely to be affected not only by LF processes but also by an oceanic source, while such a pattern was more prominent at the D-LF. The chemical species of RSCs that can exert significant influences on the photochemical production of SO2 in the LF environment were identified to be H2S, DMS, or DMDS.
Keywords: Landfill; Photochemical oxidation; RSCs; H; 2; S; SO; 2
Analysis of ozone and VOCs measured in Shanghai: A case study by Fuhai Geng; Chunsheng Zhao; Xu Tang; Guoliang Lu; Xuexi Tie (pp. 989-1001).
Shanghai Meteorological Administration has established a volatile organic compounds (VOCs) laboratory and an observational network for VOCs and ozone (O3) measurements in the city of Shanghai. In this study, the measured VOCs and O3 concentrations from 15 November (15-Nov) to 26 November (26-Nov) of 2005 in Shanghai show that there are strong day-to-day and diurnal variations. The measured O3 and VOCs concentrations have very different characterizations between the two periods. During 15-Nov to 21-Nov (defined as the first period), VOCs and O3 concentrations are lower than the values during 22-Nov to 28-Nov (defined as the second period). There is a strong diurnal variation of O3 during the second period with maximum concentrations of 40–80ppbv at noontime, and minimum concentrations at nighttime. By contrast, during the first period, the diurnal variation of O3 is in an irregular pattern with maximum concentrations of only 20–30ppbv. The VOC concentrations change rapidly from 30–50ppbv during the first period to 80–100ppbv during the second period. Two chemical models are applied to interpret the measurements. One model is a regional chemical/dynamical model (WRF-Chem) and another is a detailed chemical mechanism model (NCAR MM). Model analysis shows that the meteorological conditions are very different between the two periods, and are mainly responsible for the different chemical characterizations of O3 and VOCs between the two periods. During the first period, meteorological conditions are characterized by cloudy sky and high-surface winds in Shanghai, resulting in a higher nighttime planetary boundary layer (PBL) and faster transport of air pollutants. By contrast, during the second period, the meteorological conditions are characterized by clear sky and weak surface winds, resulting in a lower nighttime PBL and slower transport of air pollutants. The chemical mechanism model calculation shows that different VOC species has very different contributions to the high-ozone concentrations during the second period. Alkane (40ppbv) and aromatic (30ppbv) are among the highest VOC concentrations observed in Shanghai. The analysis suggests that the aromatic is a main contributor for the O3 chemical production in Shanghai, with approximately 79% of the O3 being produced by aromatic. This analysis implies that future increase in VOC (especially aromatic) emissions could lead to significant increase in O3 concentrations in Shanghai.
Keywords: VOCs; Ozone; Shanghai; WRF-Chem
Isoprene above the Eastern Mediterranean: Seasonal variation and contribution to the oxidation capacity of the atmosphere by E. Liakakou; M. Vrekoussis; B. Bonsang; Ch. Donousis; M. Kanakidou; N. Mihalopoulos (pp. 1002-1010).
Isoprene is one of the most important biogenic volatile organic compounds with large terrestrial emissions and comparatively a small oceanic source on a global scale. This marine source seems to strongly depend on environmental parameters such as phytoplankton abundance, light, temperature, wind speed, and thus, to be highly variable. However, this source can consequently affect the chemistry of the marine boundary layer on a local or mesoscale. The present study investigates the factors that control isoprene levels and estimates the marine source of isoprene and its role in the oxidizing capacity of the atmosphere at a coastal site in the East Mediterranean. More than 2000 measurements of isoprene have been conducted at Finokalia sampling station on the island of Crete over an 8-month period from February to October 2004. Isoprene varies between 5 and 1200pptv with the highest values observed in summer. The origin of the air masses determines the atmospheric abundance and the prevailing source of isoprene. According to chemical box model calculations, during daytime the isoprene observed under marine conditions is reducing hydroxyl (OH) and hydroperoxy (HO2) radicals by up to 26% and 13%, respectively, whereas, it can increase the sum of peroxy radicals by a factor of 4. At night, isoprene of marine origin is depressing nitrate radicals by up to 25% and increases the low nighttime levels of OH and HO2 radicals by up to 25% and 30%, respectively. The seawater emissions of isoprene in the area are estimated between 108 and 6×109 moleculescm−2s−1 with a strong seasonal variability.
Keywords: Isoprene; Oceanic source; Eastern Mediterranean; Oxidation capacity; Atmospheric chemistry
Spatial patterns of mobile source particulate matter emissions-to-exposure relationships across the United States by Susan L. Greco; Andrew M. Wilson; John D. Spengler; Jonathan I. Levy (pp. 1011-1025).
Assessing the public health benefits from air pollution control measures is assisted by understanding the relationship between mobile source emissions and subsequent fine particulate matter (PM2.5) exposure. Since this relationship varies by location, we characterized its magnitude and geographic distribution using the intake fraction (iF) concept. We considered emissions of primary PM2.5 as well as particle precursors SO2 and NO x from each of 3080 counties in the US. We modeled the relationship between these emissions and total US population exposure to PM2.5, making use of a source–receptor matrix developed for health risk assessment. For primary PM2.5, we found a median iF of 1.2 per million, with a range of 0.12–25. Half of the total exposure was reached by a median distance of 150km from the county where mobile source emissions originated, though this spatial extent varied across counties from within the county borders to 1800km away. For secondary ammonium sulfate from SO2 emissions, the median iF was 0.41 per million (range: 0.050–10), versus 0.068 per million for secondary ammonium nitrate from NO x emissions (range: 0.00092–1.3). The median distance to half of the total exposure was greater for secondary PM2.5 (450km for sulfate, 390km for nitrate). Regression analyses using exhaustive population predictors explained much of the variation in primary PM2.5 iF ( R2=0.83) as well as secondary sulfate and nitrate iF ( R2=0.74 and 0.60), with greater near-source contribution for primary than for secondary PM2.5. We conclude that long-range dispersion models with coarse geographic resolution are appropriate for risk assessments of secondary PM2.5 or primary PM2.5 emitted from mobile sources in rural areas, but that more resolved dispersion models are warranted for primary PM2.5 in urban areas due to the substantial contribution of near-source populations.
Keywords: Air pollution; Risk assessment; Automobiles; Environmental policy; Intake fraction; Fine particulate matter; PM; 2.5
Impact of the implementation of PM abatement technology on the ambient air levels of metals in a highly industrialised area by X. Querol; Minguillon M.C. Minguillón; A. Alastuey; E. Monfort; E. Mantilla; M.J. Sanz; F. Sanz; A. Roig; A. Renau; C. Felis; Miro J.V. Miró; Artinano B. Artíñano (pp. 1026-1040).
Data on the spatial and time (2002–2005) variation of levels of trace elements and the source attribution of these elements in the ceramic cluster of Castelló (Eastern Spain) are presented and discussed. Earlier studies concluded that metal levels in PM10 were one of the most critical parameters for attaining the EU legal requirements of the air quality standards. Levels of Li, Sc, Co, Zn, As, Se, Rb, Zr, Cd, Cs, Ce, Tl and Pb were higher than the usual range of concentration in urban areas of Spain, and some of them exceeded the concentration ranges obtained for other industrial sites in Spain. Of these elements, Zr, Zn, Pb and As (and probably Tl) may be considered as tracers of the ceramic emissions from the study area. A downward trend was observed for most of them, simultaneously, with the progressive implementation of the emission abatement techniques, especially those applied to the PM abatement of the manufacture of glaze components and the avoidance of the use of specific raw materials with high contents of impurities. At the end of the study period, the elements for which the EU sets limit or target values met the established requirements for 2013 (2005 for Pb), whereas, at the beginning of the study some elements exceeded the 2013 target values. Furthermore, a detailed discussion on the interpretation of peak concentration events and source attribution for a number of trace elements is presented. Five different sources were identified: mineral emissions (from clay use and handling), industry (mainly glaze production and use), road traffic, sea spray and the regional background influenced by a fuel oil-power plant and a petrochemical plant.
Keywords: PM; Metal; Air quality; Ceramic industry; Speciation; Abatement technology; Spain
Phase transition behaviour of sodium oleate aerosol particles by Najera Juan J. Nájera (pp. 1041-1052).
Field measurements have shown that organic surfactants are significant components of atmospheric aerosols. While fatty acids, among other surfactants, are prevalent in the atmosphere, the influence of these species on the chemical and physical properties of atmospheric aerosols remains not fully characterized. In order to assess the phase in which particles may exist, a detailed study of the deliquescence of a model surfactant aerosol has been carried out. Sodium oleate was chosen as a surfactant proxy relevant in atmospheric aerosol. Sodium oleate micelle aerosol particles were generated nebulizing a sodium oleate aqueous solution. In this study, the water uptake and phase transition of sodium oleate aerosol particles have been studied in a room temperature aerosol flow tube system (AFT) using Fourier transform infrared (FTIR) spectroscopy. Aerosol morphology and elemental composition were also analysed using scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX) techniques. The particles are homogeneously distributed as ellipsoidal-shape aggregates of micelles particles with an average size of ∼1.1μm. The deliquescence by the sodium oleate aerosol particles was monitored by infrared extinction spectroscopy, where the dried aerosol particles were exposed to increasing relative humidity as they passed through the AFT. Observations of the infrared absorption features of condensed phase liquid water enable to determine the sodium oleate deliquescence phase transition at 88±2%.
Keywords: Deliquescence; Extinction infrared spectrum; Organic aerosol; Sodium oleate micelle; Surfactant
Formation of fine particles enriched by V and Ni from heavy oil combustion: Anthropogenic sources and drop-tube furnace experiments by Ha-Na Jang; Yong-Chil Seo; Ju-Hyung Lee; Kyu-Won Hwang; Jong-Ik Yoo; Chong-Hui Sok; Seong-Heon Kim (pp. 1053-1063).
The present study attempts to investigate the emission characteristics of fine particles with special emphasis on nickel and vanadium metal elements emitted from the heavy oil combustion in industrial boilers and power plant, which are typical anthropogenic sources in Korea. A series of combustion experiments were performed to investigate the emission characteristics of particles in the size range of submicron by means of drop-tube furnace with three major domestic heavy oils. Cascade impactors were utilized to determine the size distribution of particulates as well as to analyze the partitioning enrichment of vanadium and nickel in various size ranges. Experimental results were compared with field data of particle size distribution and metal partitioning at commercial utility boilers with heavy oil combustion. Such data were interpreted by chemical equilibrium and particle growth mechanism by means of computational models. In general, fine particles were the major portion of PM10 emitted from the heavy oil combustion, with significant fraction of ultra-fine particles. The formation of ultra-fine particles through nucleation/condensation/coagulation from heavy oil combustion was confirmed by field and experimental data. Vanadium and nickel were more enriched in fine particles, particularly in ultra-fine particles. The conventional air pollution devices showed inefficient capability to remove ultra-fine particles enriched with hazardous transition metal elements such as vanadium and nickel.
Keywords: Combustion; Heavy oil; Vanadium; Nickel; Ultra-fine particles
Trends in size classified particle number concentration in subtropical Brisbane, Australia, based on a 5 year study by Mejia J.F. Mejía; D. Wraith; K. Mengersen; L. Morawska (pp. 1064-1079).
Particle number size distribution data in the range from 0.015 to 0.630μm were collected over a 5-year period in the central business district (CBD) of Brisbane, Australia. Particle size distribution was summarised by total number concentration and number median diameter (NMD) as well as the number concentration of the 0.015–0.030 ( N15–30), 0.030–0.050 ( N30–50), 0.050–0.100 ( N50–100), 0.100–0.300 ( N100–300) and 0.300–0.630 ( N300–630)μm size classes. Morning (6:00–10:00) and afternoon (16:00–19:00) measurements, the former representing fresh traffic emissions (based on the local meteorological conditions) and the latter well-mixed emissions from the CBD, during weekdays were extracted and the respective monthly mean values were estimated for time series analysis. For all size fractions, average morning concentrations were about 1.5 higher than in the afternoon whereas NMD did not vary between the morning and afternoon. The trend and seasonal components were extracted through weighted linear regression models, using the monthly variance as weights. Only the morning measurements exhibited significant trends. During this time of the day, total particle number increased by 105.7% and the increase was greater for larger particles, resulting in a shift in NMD by 7.9%. Although no seasonal component was detected the evidence against it remained weak due to the limitations of the database.
Keywords: Submicrometre particles; Ultrafine particles; Number size distribution; Time series; Regression models
Effects of exogenous nitrogen on freshwater marsh plant growth andN2O fluxes in Sanjiang Plain, Northeast China by Lihua Zhang; Changchun Song; Dexuan Wang; Yiyong Wang (pp. 1080-1090).
Field management strongly affected the emission ofN2O and plant growth from freshwater marshes. Nitrous oxide (N2O) fluxes, leaf area, plant height and above ground biomass were investigated under four N treatments (0, 6, 12 and 24gNH4NO3–Nm-2) in the freshwater marshes of Sanjiang Plain, Northeast China. The average growing seasonN2O flux was0.065±0.037,0.086±0.111,0.141±0.186,0.445±0.491mgm-2h-1, respectively, the above-ground biomass was201±49,252±40,290±47,954±115gm-2, respectively, the plant height was66.25±20.99,71.91±16.18,73.55±16.59,84.14±27.07cm, respectively. Exogenous nitrogen had a significant impact onN2O fluxes and plant growth. Compared to the non-fertilization treatment, the average growing seasonN2O flux in fertilization increased by 32%, 113%, 581%, respectively, the above-ground biomass increased by 26%, 44%, 375%, respectively, while the plant height increased by 8.5%, 11% and 27%, respectively. A quadratic relationship between the nitrogen applied rate andN2O fluxes, and a non-linear positive correlation between the nitrogen and above-ground biomass were found, while the relationship between theN2O flux and the above-ground biomass was significantly linear positive correlated after nitrogen application, so was the plant height. It was proposed that the exogenous nitrogen gives rise to considerableN2O emissions from freshwater marshes and a large fraction ofN2O was emitted to the atmosphere via the transpiration stream within the Deyeuxia angustifolia plants, which provides some quantificational data on the relationship between the nitrogen,N2O fluxes and marsh plant growth.
Keywords: Nitrogen fertilization; Plant height; Above-ground biomass; Leaf area; N; 2; O; fluxes; Field experiment
The evolution of chemical components of aerosols at five monitoring sites of China during dust storms by Ying Wang; Guoshun Zhuang; Aohan Tang; Wenjie Zhang; Yele Sun; Zifa Wang; Zhisheng An (pp. 1091-1106).
Daily PM2.5 and TSP and their chemical composition with two dust events (DS1: 9–10 March and DS2: 27–30 March) were simultaneously observed for the period of 9 March–23 April 2004 from a monitoring network over China. Five monitoring sites were performed along the transport pathway of Asian dust storm, located in Northwest, North, East, and Southeast regions of China. The dust and non-dust days exhibited different characteristics with respect to the composition and the meteorological conditions. In non-dust days, particulate pollution was found to be associated with the city economy, and it primarily consisted of the crustal, the secondary, and the carbonaceous material. In the dust episodes, significant increase in the particle concentration with a large part of the secondary components diluted by the crustal components was observed at all the sites. Particles were getting more and more acidic as the episodic dust progressed eastward. Dust particles were suggested to react with SO2/NO X/sulfate/nitrate based on the variations of SO42−/Ca2+ and NO3−/Ca2+ along the transport pathway, and the formation mechanism of sulfate and nitrate was proved to be different. Positive matrix factorization analysis showed that the sources from the upstream and the transport pathways could account for 49%, 82%, and 28% of PM mass, crust, and secondary aerosol, respectively, and the contribution decreased, as the dust made its way from source area to the coastal regions. Enrichment factors of the species presented significant correlations among different sites in the dust episodes, suggesting the significant impact of those dust emissions on the local environment.
Keywords: Dust storm; Evolution; Source contribution; PM; 2.5; TSP
Constraining the density and complex refractive index of elemental and organic carbon in biomass burning aerosol using optical and chemical measurements by G. Schkolnik; D. Chand; A. Hoffer; M.O. Andreae; C. Erlick; E. Swietlicki; Y. Rudich (pp. 1107-1118).
The role of biomass burning aerosols in the climate system is still poorly quantified, in part due to uncertainties regarding the optical properties of elemental and organic carbon (EC and OC, respectively), the main constituents of pyrogenic aerosols. In this study, we utilize comprehensive physical and chemical field measurements of biomass burning aerosols in Brazil to constrain the densities and refractive indices (RI) of EC and OC in these particles, by comparing their optically and chemically derived RI. The optically derived effective RI are retrieved from the measured absorption and scattering coefficients using a Mie scattering algorithm, and serve as a reference dataset, while the chemically derived effective RI are calculated from the measured chemical composition using electromagnetic mixing rules. The results are discussed in light of the observed combustion conditions, and in an effort to derive conclusions as to the chemical and optical properties of the usually less well-characterized components of biomass burning aerosols, namely, elemental carbon and organic matter. The best agreement between the optically and chemically derived RI was achieved by assigning a density ofρEC=1.8gcm-3 and refractive indexRIEC=1.87-0.22i to the EC component, andρ=0.9gcm-3 andRI=1.4-0i to the unidentified organic matter fraction of the particles. These parameters suggest low graphitization levels for the EC, and a dominant proportion of aliphatic compounds in the unidentified organic matter. Combining the density and RI of the unidentified organic matter with the properties of the chemically characterized organic fraction yieldsρ=1.1gcm-3 andRI=1.3-0i for the total aerosol OC.
Keywords: Biomass burning; Aerosol optical properties; Refractive index; Elemental carbon; Organic carbon