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Many studies have focused on the physicochemical properties of aerosol particles in unusually severe haze episodes instead of the more freqent and less severe hazes. Consistent with this lack of attention, the morphology and mixing state of organic matter (OM) particles in the frequent light and moderate (L&M) hazes in winter in North China Plain (NCP) have not been examined, even though OM dominates these fine particles. In the present work, morphology, mixing state, and size of organic aerosols in the L&M hazes were systematically characterized using transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy, atomic force microscopy, and nanoscale secondary ion mass spectrometer, with the comparisons among an urban site (Jinan, S1), a mountain site (Tai, S2), and a background island site (Changdao, S3) in the same hazes. Based on their morphology, the OM particles were divided into six different types: spherical (type 1), near-spherical (type 2), irregular (type 3), domelike (type 4), dispersed-OM (type 5), and OM-coating (type 6). In the three sampling sites, type 1-3 of OM particles were most abundant in the L&M hazes and most of them were internally mixed with non-OM particles. The abundant near-spherical OM particles with higher sphericity and lower aspect ratio indicate that these primary OM particles formed in cooling, polluted plumes from coal combustion and biomass burning. Based on the Si-O-C ratio in OM particles, we estimated that 71% of type 1-3 OM particles were associated with coal combustion. Our result suggests that coal combustion in residential stoves was a widespread source from urban to rural areas in the NCP. Average OM thickness which correlates with the age of the air masses in type 6 particles only slightly increased from S3 to S2 to S1, suggesting that the L&M hazes were usually dry (relative humidity < 60%) with weak photochemistry and heterogeneous reactions between aerosols and gases. We conclude that the direct emissions from these coal stoves without any pollution controls in rural areas and in urban outskirts mainly contribute into the regional L&M hazes in North China. [ABSTRACT FROM AUTHOR]

Transmission electron microscopy (TEM) was employed to obtain morphology, size, composition, and mixing state of background fine particles with diameter less than 1 µm in the Qinghai-Tibetan Plateau (QTP) during 15 September to 15 October 2013. Individual aerosol particles mainly contained secondary inorganic aerosols (SIA-sulfate and nitrate) and organics during clean periods (PM2.5: particles less than 2.5 µg m-3). The presence of KCl-NaCl associated with organics and an increase of soot particles suggest that an intense biomass burning event caused the highest PM2.5 concentrations (>30 µg m-3) during the study. A large number fraction of the fly ash-containing particles (21.73%) suggests that coal combustion emissions in the QTP significantly contributed to air pollutants at the median pollution level (PM2.5: 10-30 µg m-3). We concluded that emissions from biomass burning and from coal combustion both constantly contribute to anthropogenic particles in the QTP atmosphere. Based on size distributions of individual particles in different pollution levels, we found that gas condensation on existing particles is an important chemical process for the formation of SIA with organic coating. TEM observations show that refractory aerosols (e.g., soot, fly ash, and visible organic particles) likely adhere to the surface of SIA particles larger than 200 nm due to coagulation. Organic coating and soot on surface of the aged particles likely influence their hygroscopic and optical properties in the QTP, respectively. To our knowledge, this study reports the first microscopic analysis of fine particles in the background QTP air. [ABSTRACT FROM AUTHOR]

The mitigation of air pollution in megacities remains a great challenge because of the complex sources and formation mechanisms of aerosol particles. The 2014 Asia- Pacific Economic Cooperation (APEC) summit in Beijing serves as a unique experiment to study the impacts of emission controls on aerosol composition, size distributions, and oxidative properties. Herein, a high-resolution time-of-flight aerosol mass spectrometer was deployed in urban Beijing for real-time measurements of size-resolved non-refractory submicron aerosol (NR-PM1) species from 14 October to 12 November 2014, along with a range of collocated measurements. The average (±σ) PM1 was 41.6 (±38.9) ±gm-3 during APEC, which was decreased by 53% compared with that before APEC. The aerosol composition showed substantial changes owing to emission controls during APEC. Secondary inorganic aerosols (SIA=sulfate+nitrate+ammonium) showed significant reductions of 62-69 %, whereas organics presented much smaller decreases (35 %). The results from the positive matrix factorization of organic aerosols (OA) indicated that highly oxidized secondary OA (SOA) showed decreases similar to those of SIA during APEC. However, primary OA (POA) from cooking, traffic, and biomass burning sources were comparable to those before APEC, indicating the presence of strong local source emissions. The oxidation properties showed corresponding changes in response to OA composition. The average oxygen-to-carbon level during APEC was 0.36 (±0.10), which is lower than the 0.43 (7#177;0.13) measured before APEC, demonstrating a decrease in the OA oxidation degree. The changes in size distributions of primary and secondary species varied during APEC. SIA and SOA showed significant reductions in large accumulation modes with peak diameters shifting from ~ 650 to 400nm during APEC, whereas those of POA remained relatively unchanged. The changes in aerosol composition, size distributions, and oxidation degrees during the aging processes were further illustrated in a case study of a severe haze episode. Our results elucidated a complex response of aerosol chemistry to emission controls, which has significant implications that emission controls over regional scales can substantially reduce secondary particulates. However, stricter emission controls for local source emissions are needed for further mitigating air pollution in the megacity of Beijing. [ABSTRACT FROM AUTHOR]

The megacity of Beijing has experienced frequent severe fine particle pollution during the last decade. Although the sources and formation mechanisms of aerosol particles have been extensively investigated on the basis of ground measurements, real-time characterization of aerosol particle composition and sources above the urban canopy in Beijing is rare. In this study, we conducted real-time measurements of non-refractory submicron aerosol (NR-PM1) composition at 260m at the 325m Beijing Meteorological Tower (BMT) from 10 October to 12 November 2014, by using an aerosol chemical speciation monitor (ACSM) along with synchronous measurements of size-resolved NR-PM1 composition at near ground level using a High-Resolution Time-of- Flight Aerosol Mass Spectrometer (HR-ToF-AMS). The NR-PM1 composition above the urban canopy was dominated by organics (46 %), followed by nitrate (27 %) and sulfate (13 %). The high contribution of nitrate and high NO3-=SO42- mass ratios illustrate an important role of nitrate in particulate matter (PM) pollution during the study period. The organic aerosol (OA) was mainly composed by secondary OA (SOA), accounting for 61% on an average. Different from that measured at the ground site, primary OA (POA) correlated moderately with SOA, likely suggesting a high contribution from regional transport above the urban canopy. The Asia-Pacific Economic Cooperation (APEC) summit with strict emission controls provides a unique opportunity to study the impacts of emission controls on aerosol chemistry. All aerosol species were shown to have significant decreases of 40-80% during APEC from those measured before APEC, suggesting that emission controls over regional scales substantially reduced PM levels. However, the bulk aerosol composition was relatively similar before and during APEC as a result of synergetic controls of aerosol precursors such as SO2, NOx, and volatile organic compounds (VOCs). In addition to emission controls, the routine circulations of mountain-valley breezes were also found to play an important role in alleviating PM levels and achieving the "APEC blue" effect. The evolution of vertical differences between 260m and the ground level was also investigated. Our results show complex vertical differences during the formation and evolution of severe haze episodes that are closely related to aerosol sources and boundary layer dynamics. [ABSTRACT FROM AUTHOR]

High concentrations of fine particles (PM2.5) are frequently observed during all seasons in Beijing, China, leading to severe air pollution and human health problems in this megacity. In this study, we conducted real-time measurements of non-refractory sub-micron aerosol (NR-PM1) species (sulfate, nitrate, ammonium, chloride, and organics) in Beijing using an Aerodyne Aerosol Chemical Speciation Monitor for 1 year, from July 2011 to June 2012. This is the first long-term, highly time-resolved (~ 15min) measurement of fine particle composition in China. The seasonal average (±1 σ) mass concentration of NR-PM1 ranged from 52 (±49) μg m-3 in the spring season to 62 (±49) μg m-3 in the summer season, with organics being the major fraction (40-51 %), followed by nitrate (17-25%) and sulfate (12-17%). Organics and chloride showed pronounced seasonal variations, with much higher concentrations in winter than in the other seasons, due to enhanced coal combustion emissions. Although the seasonal variations of secondary inorganic aerosol (SIA = sulfate + nitrate + ammonium) concentrations were not significant, higher contributions of SIA were observed in summer (57-61 %) than in winter (43-46 %), indicating that secondary aerosol production is a more important process than primary emissions in summer. Organics presented pronounced diurnal cycles that were similar among all seasons, whereas the diurnal variations of nitrate were mainly due to the competition between photochemical production and gas-particle partitioning. Our data also indicate that high concentrations of NR-PM1 (> 60 µgm-3) are usually associated with high ambient relative humidity (RH) (> 50%) and that severe particulate pollution is characterized by different aerosol composition in different seasons. All NR-PM1 species showed evident concentration gradients as a function of wind direction, generally with higher values associated with wind from the south, southeast or east. This was consistent with their higher potential as source areas, as determined by potential source contribution function analysis. A common high potential source area, located to the southwest of Beijing along the Taihang Mountains, was observed during all seasons except winter, when smaller source areas were found. These results demonstrate a high potential impact of regional transport from surrounding regions on the formation of severe haze pollution in Beijing. [ABSTRACT FROM AUTHOR]

Atmospheric aerosols exert highly uncertain impacts on radiative forcing and also have detrimental effects on human health. While aerosol particles are widely characterized in megacities in China, aerosol composition, sources and particle growth in rural areas in the Tibetan Plateau remain less understood. Here we present the results from an autumn study that was conducted from 5 September to 15 October 2013 at a national background monitoring station (3295 ma.s.l.) in the Tibetan Plateau. The submicron aerosol composition and particle number size distributions were measured in situ with an Aerodyne Aerosol Chemical Speciation Monitor (ACSM) and a Scanning Mobility Particle Sizer (SMPS). The average mass concentration of submicron aerosol (PM1) is 11.9 µg m-3 (range: 1.0-78.4 µg m-3) for the entire study, which is much lower than those observed at urban and rural sites in eastern China. Organics dominated PM1 on average accounting for 43%, followed by sulfate (28%) and nitrate (1%). Positive matrix factorization analysis of ACSM organic aerosol (OA) mass spectra identified an oxygenated OA (OOA) and a biomass burning OA (BBOA). The OOA dominated OA composition accounting for 85% on average, 17% of which was inferred from aged BBOA. The BBOA contributed a considerable fraction of OA (15%) due to the burning of cow dung and straws in September. New particle formation and growth events were frequently observed (80% of time) throughout the study. The average particle growth rate is 2.0 nm h-1 (range: 0.8-3.2 nm h-1). By linking the evolution of particle number size distribution to aerosol composition, we found an elevated contribution of organics during particle growth periods and also a positive relationship between the growth rate and the fraction of OOA in OA, which potentially indicates an important role of organics in particle growth in the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

High concentrations of fine particles (PM2.5) are frequently observed during all seasons in Beijing, China, leading to severe air pollution and human health problems in this megacity. In this study, we conducted real-time measurements of non-refractory submicron aerosol (NR-PM1) species (sulfate, nitrate, ammonium, chloride, and organics) in Beijing using an Aerodyne Aerosol Chemical Speciation Monitor for 1 year, from July 2011 to June 2012. This is the first long-term, highly time-resolved (~ 15 min) measurement of fine particle composition in China. The seasonal average (±1 σ) mass concentration of NR-PM1 ranged from 52 (±49) µgm-3 in the spring season to 62 (±49) µgm-3 in the summer season, with organics being the major fraction (40-51 %), followed by nitrate (17-25 %) and sulfate (12-17 %). Organics and chloride showed pronounced seasonal variations, with much higher concentrations in winter than in the other seasons, due to enhanced coal combustion emissions. Although the seasonal variations of secondary inorganic aerosol (SIA=sulfate+nitrate+ammonium) concentrations were not significant, higher contributions of SIA were observed in summer (57-61 %) than in winter (43-46 %), indicating that secondary aerosol production is a more important process than primary emissions in summer. Organics presented pronounced diurnal cycles that were similar among all seasons, whereas the diurnal variations of nitrate were mainly due to the competition between photochemical production and gas--particle paritioning. Our data also indicate that high concentrations of NR-PM1 (> 60 µgm-3) are usually associated with high ambient relative humidity (RH) (> 50 %) and that severe particulate pollution is characterized by different aerosol composition in different seasons. All NR-PM1 species showed evident concentration gradients as a function of wind direction, generally with higher values associated with wind from the south, southeast or east. This was consistent with their higher potential as source areas, as determined by potential source contribution function analysis. A common high potential source area, located to the southwest of Beijing along the Taihang Mountains, was observed during all seasons except winter, when smaller source areas were found. These results demonstrate a high potential impact of regional transport from surrounding regions on the formation of severe haze pollution in Beijing. [ABSTRACT FROM AUTHOR]

Atmospheric aerosols exert highly uncertain impacts on radiative forcing and also have detrimental effects on human health. While aerosol particles are widely characterized in megacities in China, aerosol composition, sources and particle growth in rural areas in the Tibetan Plateau remain less understood. Here we present the results from an autumn study that was conducted from 5 September to 15 October 2013 at a national background monitoring station (3295 m a.s.l.) in the Tibetan Plateau. The submicron aerosol composition and particle number size distributions were measured in situ with an Aerodyne Aerosol Chemical Speciation Monitor (ACSM) and a Scanning Mobility Particle Sizer (SMPS). The average mass concentration of submicron aerosol (PM1) is 11.9 µg m-3 (range: 1.0-78.4 µg m-3) for the entire study, which is much lower than those observed at urban and rural sites in eastern China. Organics dominated PM1 on average accounting for 43%, followed by sulfate (28%) and nitrate (1%). Positive matrix factorization analysis of ACSM organic aerosol (OA) mass spectra identified an oxygenated OA (OOA) and a biomass burning OA (BBOA). The OOA dominated OA composition accounting for 85% on average, 17% of which was inferred from aged BBOA. The BBOA contributed a considerable fraction of OA (15%) due to the burning of cow dung and straws in September. New particle formation and growth events were frequently observed (80% of time) throughout the study. The average particle growth rate is 2.0 nm h-1 (range: 0.8-3.2 nm h-1). By linking the evolution of particle number size distribution to aerosol composition, we found an elevated contribution of organics during particle growth periods and also a positive relationship between the growth rate and the fraction of OOA in OA, which potentially indicates an important role of organics in particle growth in the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Four extreme haze episodes occurred in October 2014 in the North China Plain (NCP). To clarify the formation mechanism of hazes in the autumn, strengthened observations were conducted in Beijing from 5 October to 2 November. The meteorological parameters, satellite data, chemical compositions and optical properties of aerosols were obtained. The hazes originated from NCP, developing in the southwest and northeast directions, with the highest concentration of PM2.5 of 469 µgm-3 in Beijing. NCP was dominated by a weak high pressure system during the haze episode, which resulted in low surface wind speed and relatively stagnant weather. Moreover, the wind slowed down around Beijing city. The secondary aerosols NO3- was always higher than that of SO42-, which indicated the motor vehicles played a more important part in the hazes in October 2014, even though the oxidation rate from SO2 to SO42- was faster than that of NOx to NO3- . Sudden increases of the concentrations of organic matter, Cl- and BC (Black carbon) before each haze episode implied that regional transport of pollutants by biomass burning was important for haze formation during the autumn. A satellite map of fire points and the backward trajectories of the air masses also indicated this pollution source. The distinct decrease in the PBL (planetary boundary layer) height during four haze episodes restrained the vertical dispersion of the air pollutants. Water vapor also played a vital role in the formation of hazes by accelerating the chemical transformation of secondary pollutants, leading to hygroscopic growth of aerosols and altering the thermal balance of the atmosphere. [ABSTRACT FROM AUTHOR]

Atmospheric submicron particulate matter (PM1) is one of the most significant pollution components in China. Despite its current popularity in the studies of aerosol chemistry, the characteristics, sources and evolution of atmospheric PM1 species in the East China are still poorly understood. Particular situations are the two harvest seasons, namely summer wheat harvest and autumn rice harvest. An Aerodyne Aerosol Chemical Speciation Monitor (ACSM) was deployed for online continuous monitoring of PM1 components during summer and autumn harvest seasons in urban Nanjing situated in the Yangtze River Delta (YRD) region of China. Results show that organic aerosol (OA) was the most abundant PM1 component, accounting for 39% and 41% of the total mass during the summer and autumn harvest periods, respectively. Positive matrix factorization (PMF) analysis resolved three OA components, i.e., hydrocarbon-like OA (HOA), biomass burning OA (BBOA), and oxygenated OA (OOA), which on average accounted for 19% (30 %), 17% (18 %), and 64% (52 %) of the total OA mass concentrations during the summer (autumn) harvest respectively. The BBOA mass fraction increases with an increase of high PM1 mass loadings (PM1 > 100 µgm-3), implying that BBOA plays a dominate role in high PM pollution during the harvest seasons. The mass concentrations of BBOA correlate well with the mass concentration of water-soluble potassium (K+), indicating that the atmospheric K+ is a good tracer for both wheat and rice straw burning during the harvest seasons. The BBOA mass concentrations for the summer and autumn harvest can be estimated as BBOA = 36.7 x (m/z 60-0.26% x OA) and = 41.4 x (m/z 60-0.26% x OA), respectively, m/z 60 as an identified marker for levoglucosan-like species. The OA mass decreases with the aging of BB plumes, implying that the fresh BB plumes contribute to atmospheric OA burden significantly. Combination of back-trajectory analysis with local wind indicates that the heavy pollution during the harvest seasons in the YRD region was found to be associated with transport processes and local source emissions. [ABSTRACT FROM AUTHOR]

Measurements of gaseous pollutants, including ozone (O3), sulfur dioxide (SO2), nitrogen oxides (NOx = NO + NO2), carbon monoxide (CO), particle number concentrations (5.6-560 nm and 0.47-30 μm), and meteorological parameters (T, RH, P) were conducted during the Program of Campaigns of Air Quality Research in Beijing and Surrounding Region (CAREBeijing) from 27 August through 13 October 2008. The data of total 18 flights (70 h flight time) from the ground to 2100 m were obtained by a Yun-12 aircraft in the southern surrounded areas of Beijing (38° N-40° N, 114° E-118° E). This measurement was to characterize the regional variation of air pollution during and after the Olympics of 2008, the impacts of different transport direction and possible influencing factors. Results suggested that four different groups of transport sources influenced the pollution level of pollutants with the consideration of the backward trajectory analysis, including: (1) the pollutant transport of the southern direction with higher pollutants level; (2) the cleaner long-range transport of the northern or northwestern direction with lower pollutants level; (3) the transport from the eastern direction with characteristics of sea sources, i.e. middle level of gases pollutants and higher particle concentration; (4) the transport of mixing directions, i.e. lower altitudes from the pollutant transport direction or local pollution but higher altitudes from the clean transport direction. Additionally, the relatively long-lived CO was shown to be a possible transport tracer of long-range transport of northwestern direction especially on the higher altitudes. Three factors influenced the size distribution of particles, i.e. air mass transport direction, ground source emissions and meteorological influences were also discussed. [ABSTRACT FROM AUTHOR]

Air pollution is a major environmental concern among all seasons in megacity Beijing, China. Here we present the results from a winter study that was conducted from 21 November 2011 to 20 January 2012 with an Aerodyne Aerosol Chemical Speci-ation Monitor (ACSM) and various collocated instruments. The non-refractory sub-micron aerosol (NR-PM1) species vary dramatically with clean periods and pollution episodes alternating frequently. Compared to summer, wintertime submicron aerosols show much enhanced organics and chloride, which on average account for 52% and 5%, respectively of the total NR-PM1 mass. All NR-PM1 species show quite different diurnal behaviors between summer and winter. For example, the wintertime nitrate presents a gradual increase during daytime and correlates well with secondary organic aerosol (OA), indicating a dominant role of photochemical production over gas-particle partitioning. Positive matrix factorization was performed on ACSM OA mass spectra, and identified three primary OA (POA) factors, i.e. hydrocarbon-like OA (HOA), cooking OA (COA), and coal combustion OA (CCOA), and one secondary factor, i.e. oxygenated OA (OOA). The POA dominates OA during wintertime, contributing 69% with the rest of 31 % being SOA. Further, all POA components show pronounced diurnal cycles with the highest concentrations occurring at nighttime. CCOA is the largest primary source during the heating season, on average accounting for 33% of OA and 17% of NR-PM1. CCOA also plays a significant role in chemically-resolved particulate matter (PM) pollution as its mass contribution increases linearly as a function of NR-PM1 mass loadings. The SOA however presents a reversed trend, which might indicate the limited SOA formation during high PM pollution episodes in winter. The effects of meteorology on PM pollution and aerosol processing were also explored. In particular, the sulfate mass is largely enhanced during periods with high humidity because of fog processing of high concentration of precursor SO2. In addition, the increased traffic-related HOA emission at low temperature is also highlighted. [ABSTRACT FROM AUTHOR]

The high resolution mass spectra of organic and inorganic aerosols from aerosol mass spectrometer (AMS) measurements were first combined into positive matrix factorization (PMF) analysis to investigate the sources and evolution processes of atmospheric aerosols. The new approach is able to study the mixing of organic aerosols (OA) and inorganic species, the acidity of OA factors, and the fragment ion patterns related to photochemical processing. In this study, PMF analysis of the unified AMS spectral matrices resolved 8 factors for the submicron aerosols measured at Queens College in New York City in summer 2009. The hydrocarbon-like OA (HOA) and cooking OA (COA) contain very minor inorganic species, indicating the different sources and mixing characteristics between primary OA and secondary species. The two factors that are primarily ammonium sulfate (SO4-OA) and ammonium nitrate (NO3-OA), respectively, are overall neutralized, of which the OA in SO4-OA shows the highest oxidation state (O/C = 0.69) among OA factors. The semi-volatile oxygenated OA comprises two components, i.e., a less oxidized (LO-OOA) and a more oxidized (MO-OOA). The MO-OOA represents a local photochemical product with the diurnal profile exhibiting a pronounced noon peak, consistent with those of formaldehyde (HCHO) and Ox (=O3 +NO2). The much higher NO+/NO+2 fragment ion ratio in MO-OOA than that from ammonium nitrate alone provides evidence for the formation of organic nitrates. The amine-related nitrogenenriched OA (NOA) contains ∼25% of acidic inorganic salts, elucidating the formation of secondary OA from amines in acidic environments. The size distributions derived from 3-dimensional size-resolved mass spectra show distinct diurnal evolving behaviors for different OA factors, but overall a progressing evolution from smaller to larger particle mode as a function of oxidation states. Our results demonstrate that PMF analysis by incorporating inorganic aerosols is of importance for gaining more insights into the sources and processes, mixing characteristics, and acidity of OA. [ABSTRACT FROM AUTHOR]

Organic tracer compounds of tropospheric aerosols, as well as organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and stable carbon isotope ratios (δC) of total carbon (TC) have been investigated for aerosol samples collected during early and late periods of Mount Tai experiment 2006 (MTX2006) field campaign in North China Plain. Total solvent extracts were investigated by gas chromatography/mass spectrometry. More than 130 organic compounds were detected in the aerosol samples. They were grouped into twelve organic compound classes, including biomass burning tracers, biogenic primary sugars, biogenic secondary organic aerosol (SOA) tracers, and anthropogenic tracers such as phthalates, hopanes and polycyclic aromatic hydrocarbons (PAHs). In early June when the field burning activities of wheat straws in North China Plain were very active, the total identified organics (2090±1170 ngm-3) were double those in late June (926±574 ngm-3). All the compound classes were more abundant in early June than in late June, except phthalate esters, which were higher in late June. Levoglucosan (88-1210 ngm-3, 403 ngm-3) was found as the most abundant single compound in early June, while diisobutyl phthalate was the predominant species in late June. During the biomass-burning period in early June, the diurnal trends of most of the primary and secondary organic aerosol tracers were characterized by the concentration peaks observed at mid-night or in early morning, while in late June most of the organic species peaked in late afternoon. This suggests that smoke plumes from biomass burning can uplift the aerosol particulate matter to a certain altitude and then transported to and encountered the summit of Mt. Tai during nighttime. On the basis of the tracer-based method for the estimation of biomass-burning OC, fungal-spore OC and biogenic secondary organic carbon (SOC), we estimate that an average of 24% (up to 64 %) of the OC in the Mt. Tai aerosols was due to biomass burning in early June, followed by the contribution of isoprene SOC (mean 4.3 %). In contrast, isoprene SOC was the main contributor (6.6%) to OC, and only 3.0% of the OC was due to biomass burning in late June. In early June, δ13C of TC (-26.6% to -23.2%, mean -25.0%) were lower than those (-23.9% to -21.9% , mean -22.9%) in late June. In addition, a strong anti-correlation was found between levoglucosan and δ13C values. This study demonstrates that crop-residue burning activities can significantly enhance the organic aerosol loading and alter the organic molecular compositions and stable carbon isotopic compositions of aerosol particles in the troposphere over North China Plain. [ABSTRACT FROM AUTHOR]

Knowledge of the variations of mass concentration, chemical composition and size distributions of submicron aerosols near roadways is of importance for reducing exposure assessment uncertainties in health effects studies. The goal of this study is to deploy and evaluate an Atmospheric Sciences Research Center-Mobile Laboratory (ASRC-ML), equipped with a suite of rapid response instruments for characterization of traffic plumes, adjacent to the Long Island Expressway (LIE) -- a high-traffic highway in the New York City Metropolitan Area. In total, four measurement periods, two in the morning and two in the evening were conducted at a location approximately 30m south of the LIE. The mass concentrations and size distributions of non-refractory submicron aerosol (NR-PM1) species were measured in situ at a time resolution of 1 min by an Aerodyne High-Resolution Time-of-Flight Aerosol Mass Spectrometer, along with rapid measurements (down to 1Hz) of gaseous pollutants (e.g., HCHO, NO2, NO, O3, and CO2, etc.), black carbon (BC), and particle number concentrations and size distributions. The particulate organics varied dramatically during periods with highest traffic influences from the nearby roadway. The variations were mainly observed in the hydrocarbon-like organic aerosol (HOA), a surrogate for primary OA from vehicle emissions. The inorganic species (sulfate, ammonium, and nitrate) and oxygenated OA (OOA) showed much smoother variations -- with minor impacts from traffic emissions. The concentration and chemical composition of NR-PM1 also varied differently on different days depending on meteorology, traffic intensity and vehicle types. Overall, organics dominated the traffic-related NR-PM1 composition (> 60%) with HOA being the major fraction of OA. The traffic-influenced organics showed two distinct modes in mass-weighted size distributions, peaking at ~ 120 nm and 500 nm (vacuum aerodynamic diameter, Dva ), respectively. OOA and inorganic species appear to be internally mixed in the accumulation mode peaking at ~ 500--600 nm. The enhancement of organics in traffic emissions mainly occurred at ultrafine mode dominated by HOA, with little relation to the OOA-dominated accumulation mode. From Fast Mobility Particle Sizer (FMPS)measurements, a large increase in number concentration at ~10 nm (mobility number mean diameter, Dm) was also found due to traffic influence; though these particles typically contribute a minor fraction of total particle mass. Results here may have significant implications for near-highway air pollution characterization and exposure assessments. Our results suggest that exposure assessments must take into account the rapid variations of aerosol chemistry over short distances near roadways, and also that long-term monitoring of air pollutants throughout the day on different types of days is necessary to accurately gauge exposure to individuals. [ABSTRACT FROM AUTHOR]

We have investigated an aerosol processing and evolution event from 21-22 July during the summer 2009 Field Intensive Study at Queens College in New York City (NYC). The evolution processes are characterized by three consecutive stages: (1) aerosol wet scavenging, (2) nighttime nitrate formation, and (3) photochemical production and evolution of secondary aerosol species. Our results suggest that wet scavenging of aerosol species tends to be strongly related to their hygroscopicities and also mixing states. The scavenging leads to a significant change in bulk aerosol composition and average carbon oxidation state because of scavenging efficiencies in the following order: sulfate > low-volatility oxygenated organic aerosol (LV-OOA) > semi-volatile OOA (SV-OOA) > hydrocarbon-like OA (HOA). The second stage involves a quick formation of nitrate from heterogeneous reactions at nighttime. During the third stage, simultaneous increases of sulfate and SV-OOA were observed shortly after sunrise, indicating secondary aerosol formation. Organic aerosol particles become highly oxidized in ~half day as the result of photochemical processing, consistent with previously reported results from the CO-tracer method (OA/ΔCO). The photochemical reactions appear to progress gradually associated with a transformation of semi-volatile OOA to low-volatility species based on the evolution trends of oxygen-to-carbon (O/C) ratio, relationship between f44 (fraction of m/z 44 in OA) and f43 (fraction of m/z 43 in OA), and size evolution of OOA and HOA. Aerosols appear to become more internally mixed during the processing. Our results suggest that functionalization by incorporation of both C and O plays a major role in the early period of OA oxidation (O/C <0.5). Our results also show that photochemical production of LV-OOA during this event is approximately a few hours behind of sulfate production, which might explain the sometimes lack of correlations between LV-OOA and sulfate, two secondary aerosol species which often exist in internal mixtures over regional scales. [ABSTRACT FROM AUTHOR]