Major Aerosol Constituents Research Articles

Tracer-based source apportioning of atmospheric organic carbon and the influence of anthropogenic emissions on secondary organic aerosol formation in Hong Kong

Abstract. Here we conducted comprehensive chemical characterization and source apportionment of 49 PM2.5 samples collected in Hong Kong. Besides the major aerosol constituents, 39 polar organic species, including 14 secondary organic aerosol (SOA) tracers of isoprene, monoterpenes, β-caryophyllene, and naphthalene, were quantified using gas chromatography–mass spectrometry (GC–MS). Six factors, i.e., SOA, secondary sulfate (SS), biomass burning (BB)/SOA, sea salt, marine vessels, and vehicle emissions, were apportioned by positive matrix factorization (PMF) as the major sources of ambient organic carbon (OC) in Hong Kong. The secondary formation, including OC from SOA, SS, and aging of BB plume, was the leading contributor to OC (51.4 %, 2.15 ± 1.37 µg C m−3) throughout the year. We then applied a tracer-based method (TBM) to estimate the SOA formation from the photo-oxidation of four selected precursors, and monoterpene SOA was the most abundant. A Kintecus kinetic model was used to examine the formation channels of isoprene SOA, and the aerosol-phase ring-opening reaction of isoprene epoxydiols (IEPOXs) was found to be the dominant formation pathway. Consistently, IEPOX tracers contributed 94 % to total GC–MS-quantified isoprene SOA tracers. The TBM-estimated secondary organic carbon (SOCTBM) and PMF-apportioned SOC (SOCPMF) showed similar temporal trends; however, SOCTBM only accounted for 26.5 % of SOCPMF, indicating a large fraction of ambient SOA was from other reaction pathways or precursors. Results of Pearson's R and multivariate linear regression analysis showed that NOx processing played a key role in both daytime and nighttime SOA production in the region. Moreover, sulfate had a significant positive linear relationship with SOCPMF and SS-related SOC, and particle acidity was significantly correlated with SOC from the aging of BB.

Compositions and mixing states of aerosol particles by aircraft observations in the Arctic springtime, 2018

Abstract. Aerosol particles were collected at various altitudes in the Arctic during the Polar Airborne Measurements and Arctic Regional Climate Model Simulation Project 2018 (PAMARCMiP 2018) conducted in the early spring of 2018. The composition, size, number fraction, and mixing state of individual aerosol particles were analyzed using transmission electron microscopy (TEM), and their sources and transport were evaluated by numerical model simulations. We found that sulfate, sea-salt, mineral-dust, K-bearing, and carbonaceous particles were the major aerosol constituents. Many particles were composed of two or more compositions that had coagulated and were coated with sulfate, organic materials, or both. The number fraction of mineral-dust and sea-salt particles decreased with increasing altitude. The K-bearing particles increased within a biomass burning (BB) plume at altitudes > 3900 m, which originated from Siberia. Chlorine in sea-salt particles was replaced with sulfate at high altitudes. These results suggest that the sources, transport, and aging of Arctic aerosols largely vary depending on the altitude and air-mass history. We also provide the occurrences of solid-particle inclusions (soot, fly-ash, and Fe-aggregate particles), some of which are light-absorbing particles. They were mainly emitted from anthropogenic and biomass burning sources and were embedded within other relatively large host particles. Our TEM measurements revealed the detailed mixing state of individual particles at various altitudes in the Arctic. This information facilitates the accurate evaluation of the aerosol influences on Arctic haze, radiation balance, cloud formation, and snow/ice albedo when deposited.

Individual particle analysis of marine aerosols collected during the North\u2013South transect cruise in the Pacific Ocean and its marginal seas

Sea-salt particles are major aerosol constituents in the marine boundary layer (MBL) and are chemically modified by acidic substances from anthropogenic, volcanic, and biogenic sources. When these acidic substances react with sea-salt particles, they can be easily scavenged from the MBL. This scavenging process influences the concentration of cloud condensation nuclei in the MBL. In this study, differences in chemical compositions of sea-salt particles collected over the Pacific Ocean and its marginal seas were investigated based on an individual particle analysis. The sources of the acidic substances that modified sea-salt particles were also estimated. Approximately 70% of the analyzed particles were fresh sea-salt particles. However, a sample collected near Guam was dominated by sulfates and was affected by polluted air masses that originated over the Asian continent. The aerosols collected around the Aleutian Islands included a large number of sulfates and modified sea-salt particles. Individual particle composition analyses indicate that these sea-salt particles were modified by methanesulfonic acid produced from marine biota and sulfuric acid from volcanic gas from the Kamchatka Peninsula. The gravitational deposition velocities of sulfates and modified sea-salt particles were calculated based on measured particle sizes. The results suggested that if acidic substances react with sea-salt particles, their lifetime in the atmosphere could be shortened due to dry deposition. Therefore, it is necessary to consider the scavenging effect of sea-salt particles for estimating the climate cooling effect by clouds over the ocean.

Regional sulfate drives long-term rise in AOD over megacity Kolkata, India

We present here the first long-term (2001–2017) record of aerosol optical depth (AOD; interchangeably, AOT) and contributions of aerosol chemical components to light extinction over Kolkata, the second-most polluted metropolis in India. For this purpose, we use daily gridded MODIS AOD measurements coupled with modeled AOT for 5 major aerosol constituents – sulfate, sea-salt, dust, organic carbon (OC) and black carbon (BC), from the MERRA-2 reanalysis system. We find that AOD over Kolkata has increased significantly (32% overall, 0.010 y−1; Mann-Kendall test with Thiel-Sen slope estimation; p < 0.01) over the past 17 y to a mean of 0.74 ± 0.10 in 2017, and an overwhelming majority of this increase is driven by a concurrent rise (70% overall, 0.007 y−1, p < 0.01) in sulfate AOT. This is followed by smaller but significant enhancements in OC (40% overall, 0.002 y−1, p < 0.01) and BC (20% overall, 0.0004 y−1, p < 0.01) AOT. Although a non-trivial fraction (24%) of AOT is associated with natural emissions (sea-salt and dust), these do not exhibit significant trends over time and therefore are not instrumental in driving the observed AOD rise. A concentration-weighted trajectory (CWT) analysis shows that sulfate aerosol over Kolkata is mostly regional (within ∼250 km) during winter and post-monsoon with significant footprints over thermal power plant clusters in neighboring states and areas with considerable residential biofuel use (eastern Indo-Gangetic Plain (IGP) and the Ganges-Brahmaputra Basin). In comparison, BC and OC AOT show a significant long-range component (∼1800 km) originating from northwestern and central IGP, especially during post-monsoon, when open agricultural residue burning is rampant. Overall, these results provide a preliminary indication that a considerable fraction of aerosol light extinction over Kolkata might be related to non-local, atmospherically transported aerosol. Once validated by ground-based measurements, these results would reinforce the need to bring regional and long-range emissions, in addition to within-the-city emissions, under the purview of air quality management policies.

On the implications of aerosol liquid water and phase separation for organic aerosol mass.

Organic compounds and liquid water are major aerosol constituents in the southeast United States (SE US). Water associated with inorganic constituents (inorganic water) can contribute to the partitioning medium for organic aerosol when relative humidities or organic matter to organic carbon (OM/OC) ratios are high such that separation relative humidities (SRH) are below the ambient relative humidity (RH). As OM/OC ratios in the SE US are often between 1.8 and 2.2, organic aerosol experiences both mixing with inorganic water and separation from it. Regional chemical transport model simulations including inorganic water (but excluding water uptake by organic compounds) in the partitioning medium for secondary organic aerosol (SOA) when RH > SRH led to increased SOA concentrations,· particularly at night. Water uptake to the organic phase resulted in even greater SOA concentrations as a result of a positive feedback in which water uptake increased SOA, which further increased aerosol water and organic aerosol. Aerosol properties· such as the OM/OC and hygroscopicity parameter (κorg), were captured well by the model compared with measurements during the Southern Oxidant and Aerosol Study (SOAS) 2013. Organic nitrates from monoterpene oxidation were predicted to be the least water-soluble semivolatile species in the model, but most biogenically derived semivolatile species in the Community Multiscale Air Quality (CMAQ) model were highly water soluble and expected to contribute to water-soluble organic carbon (WSOC). Organic aerosol and SOA precursors were abundant at night, but additional improvements in daytime organic aerosol are needed to close the model–measurement gap. When taking into account deviations from ideality, including both inorganic (when RH > SRH) and organic water in the organic partitioning medium reduced the mean bias in SOA for routine monitoring networks and improved model performance compared to observations from SOAS. Property updates from this work will be released in CMAQ v5.2.

Horizontal distributions of aerosol constituents and their mixing states in Antarctica during the JASE traverse

Abstract. Measurements of aerosol number concentrations and direct aerosol sampling were conducted on continental Antarctica during the traverse of the Japanese–Swedish joint Antarctic expedition (JASE) from 14 November 2007 until 24 January 2008. Aerosol concentrations in background conditions decreased gradually with latitude in inland regions during the traverse. The lowest aerosol number concentrations were 160 L−1 in Dp &gt; 0.3 μm, and 0.5 L−1 in Dp 2 μm. In contrast, aerosol concentrations reached 3278 L−1 in Dp &gt; 0.3 μm, and 215 L−1 in Dp &gt; 2 μm under strong wind conditions. The estimated aerosol mass concentrations were 0.04–5.7 μg m−3. Single particle analysis of aerosol particles collected during the JASE traverse was conducted using a scanning electron microscope equipped with an energy dispersive x ray spectrometer. Major aerosol constituents were sulfates in fine mode, and sulfate, sea salts, modified sea salts, and fractionated sea salts in coarse mode. K-rich sulfates, Mg-rich sulfate, Ca-rich sulfates, and minerals were identified as minor aerosol constituents. Horizontal features of Cl / Na ratios imply that sea-salt modification (i.e. Cl loss) occurred on the Antarctic continent during the summer. Most sea-salt particles in the continental region near the coast were modified with acidic sulfur species such as H2SO4 and CH3SO3H. By contrast, acidic species other than the acidic sulfur species (likely HNO3) contributed markedly to sea-salt modification in inland areas during the traverse. Mg-rich sea-salt particles and Mg-free sea-salt particles were present in coarse and fine modes from the coast to inland areas. These sea-salt particles might be associated with sea-salt fractionation on the snow surface of continental Antarctica.

One-year observations of size distribution characteristics of major aerosol constituents at a coastal receptor site in Hong Kong – Part 1: Inorganic ions and oxalate

Abstract. Size distribution data of major aerosol constituents are essential in source apportioning of visibility degradation, testing and verification of air quality models incorporating aerosols. We report here 1-year observations of mass size distributions of major inorganic ions (sulfate, nitrate, chloride, ammonium, sodium, potassium, magnesium and calcium) and oxalate at a coastal suburban receptor site in Hong Kong, China. A total of 43 sets of size-segregated samples in the size range of 0.056–18 μm were collected from March 2011 to February 2012. The size distributions of sulfate, ammonium, potassium and oxalate were characterized by a dominant droplet mode with a mass mean aerodynamic diameter (MMAD) in the range of ~ 0.7–0.9 μm. Oxalate had a slightly larger MMAD than sulfate on days with temperatures above 22 °C as a result of the process of volatilization and repartitioning. Nitrate was mostly dominated by the coarse mode but enhanced presence in fine mode was detected on winter days with lower temperature and lower concentrations of sea salt and soil particles. This data set reveals an inversely proportional relationship between the fraction of nitrate in the fine mode and product of the sum of sodium and calcium in equivalent concentrations and the dissociation constant of ammonium nitrate (i.e., (1/([Na+] + 2[Ca2+]) × (1/Ke')) when Pn_fine is significant (&gt; 10%). The seasonal variation observed for sea salt aerosol abundance, with lower values in summer and winter, is possibly linked with the lower marine salinities in these two seasons. Positive matrix factorization was applied to estimate the relative contributions of local formation and transport to the observed ambient sulfate level through the use of the combined data sets of size-segregated sulfate and select gaseous air pollutants. On average, the regional/super-regional transport of air pollutants was the dominant source at this receptor site, especially on high-sulfate days while local formation processes contributed approximately 30% of the total sulfate. This work provides field-measurement-based evidence important for understanding both local photochemistry and regional/super-regional transport in order to properly simulate sulfate aerosols in air quality models.

Characterization of secondary aerosol and its extinction effects on visibility over the Pearl River Delta Region, China

Aerosol samples collected from July 2007 to March 2008 were used to obtain major aerosol constituents in an urban location in the Pearl River Delta Region (PRD), China. The minimum organic carbon (OC)/elemental carbon (EC) ratio was used to calculate the primary and secondary organic carbon and the extinction effect of the secondary aerosol on visibility was estimated. As indicated in the analysis, the mass of secondary aerosol takes up 50% of the total mass of PM2.5; the OC/EC ratio is larger than 2 and there are significant characteristics of secondary aerosol generation; the levels of secondary OC are comparable with those of sulfate; and there is obvious enrichment of secondary aerosol on more polluted days. In a dry environment, the extinction weight is 59% for the secondary aerosol, while it is as high as 82% if the environment is highly humid (relative humidity [RH] = 95%). The hygroscopic growth of the aerosol can reduce visibility greatly; the secondary aerosol shares much larger quotas on more polluted days. For the Pearl River Delta (PRD), secondary aerosol and carbonaceous aerosol, especially secondary organic carbon (SOC), are a very acute problem; the study of the generating mechanism and sources for secondary aerosol is the key to the effort of controlling visibility in this region. The equation set forth in IMPROVE experiments can only be referenced but is not applicable to evaluate the extinction effect of individual aerosol components on visibility in the PRD region. Implications: The extinction effects on visibility by different constituents are studied in this work using compositional data derived from the measurements, with special efforts on examining the extinction of secondary aerosol and the enrichment and extinction contributions of the constituents with the variation of pollution level and relative humidity, so as to provide a scientific basis for the mitigation of atmospheric aerosol pollution and improving visibility in the PRD of China.

Chemical characteristics of PM2.5 and organic aerosol source analysis during cold front episodes in Hong Kong, China

In this study, we investigate the influence of long-range transport (LRT) episodes brought in by cold front on the concentration levels of PM2.5, major aerosol constituents, organic tracers, and PM2.5 source characteristics in Hong Kong, China. PM2.5 samples were collected during January–March 2004 and January–March 2005 and analyzed for major constituents and organic tracer species. Synoptic weather conditions and characteristics of common air pollutants were used to categorize the sampling days to three groups, i.e., groups mainly affected by local emissions or regional transport (RT) or cold front LRT. Concentrations of PM2.5 mass and its major constituents during cold-front days were lower than those during RT-dominated periods but higher than those during local emissions-dominated periods. Source apportionment using chemical mass balance (CMB) indicates that vehicular exhaust was a significant primary OC source of mainly local emissions, making average contributions of 1.82, 1.50, and 2.39μgCm−3 to OC in the local, LRT, and RT sample groups, respectively. During cold front periods, primary OC concentrations attributable to biomass burning and coal combustion were approximately triple and double, respectively, those during periods dominated by local emissions. Suspended dust, a minor primary OC source (0.24–0.40μgCm−3), also showed increased contribution during cold fronts. The unexplained OC by CMB (i.e., total OC minus apportioned primary OC), an approximate indicator for secondary OC, was a significant fraction of OC (>48%) and its mass concentration was much higher in the cold front LRT and RT sample groups (6.37 and 9.48μgCm−3) than in the local sample group (3.8μgCm−3). Source analysis as well as tracer concentration variation shows that biomass burning OC and water soluble organic carbon (WSOC) were correlated, suggesting biomass burning as a significant contributor to WSOC.

Optical properties and chemical composition of aerosol particles at an urban location: An estimation of the aerosol mass scattering and absorption efficiencies

We investigated aerosol optical properties, mass concentration and chemical composition over a 1 year period (from March 2006 to February 2007) at an urban site in Southern Spain (Granada, 37.18°N, 3.58°W, 680 m above sea level). Light‐scattering and absorption measurements were performed using an integrating nephelometer and a MultiAngle Absorption Photometer (MAAP), respectively, with no aerosol size cut‐off and without any conditioning of the sampled air. PM10 and PM1 (ambient air levels of atmospheric particulate matter finer than 10 and 1 microns) were collected with two high volume samplers, and the chemical composition was investigated for all samples. Relative humidity (RH) within the nephelometer was below 50% and the weighting of the filters was also at RH of 50%. PM10 and PM1 mass concentrations showed a mean value of 44 ± 19 μg/m3 and 15 ± 7 μg/m3, respectively. The mineral matter was the major constituent of the PM10–1 fraction (contributing more than 58%) whereas organic matter and elemental carbon (OM+EC) contributed the most to the PM1 fraction (around 43%). The absorption coefficient at 550 nm showed a mean value of 24 ± 9 Mm−1 and the scattering coefficient at 550 nm presented a mean value of 61 ± 25 Mm−1, typical of urban areas. Both the scattering and the absorption coefficients exhibited the highest values during winter and the lowest during summer, due to the increase in the anthropogenic contribution and the lower development of the convective mixing layer during winter. A very low mean value of the single scattering albedo of 0.71 ± 0.07 at 550 nm was calculated, suggesting that urban aerosols in this site contain a large fraction of absorbing material. Mass scattering and absorption efficiencies of PM10 particles exhibited larger values during winter and lower during summer, showing a similar trend to PM1 and opposite to PM10–1. This seasonality is therefore influenced by the variations on PM composition. In addition, the mass scattering efficiency of the major aerosol constituents in PM10 were also calculated applying the multilinear regression (MLR) analysis. Among all of them, the most efficient in terms of scattering was sulfate ion (7 ± 1 m2g−1) while the least efficient was the mineral matter (0.2 ± 0.3 m2g−1). On the other hand, we found that the absorption process was mainly dominated by carbonaceous particles.

Seasonal features of ultrafine particle volatility in the coastal Antarctic troposphere

Abstract. The size distribution and volatility of ultrafine aerosol particles were measured using scanning mobility particle sizer and thermodenuder at Syowa Station during the 46–47 Japanese Antarctic Research Expeditions (2005–2007). The relative abundance of non-volatile particles in a 240 °C scan was approximately 20% during the summer, whereas the abundance of non-volatile particles increased by &gt;90% during the winter–spring. Most ultrafine particles were volatilized at temperature of 150–210 °C. This volatility was consistent well to major aerosol constituents (NH4+, SO42− and CH3SO3−) during the summer. In contrast, major constituents of ultrafine particles were sea-salts (Na+ and Cl−) in winter–spring. Therefore, the seasonal feature of volatility of ultrafine particles at Syowa was associated with seasonal variations of the major aerosol constituents. Although the relative abundance of non-volatile particles was usually higher during the winter–spring, the abundance dropped occasionally to &lt;30%. The lower abundance of non-volatile ultrafine particles during winter–spring corresponded to the lower number concentration of ultrafine particles and transport from the free troposphere over Antarctica.

Roadside and rooftop measurements of polycyclic aromatic hydrocarbons in PM2.5 in urban Guangzhou: Evaluation of vehicular and regional combustion source contributions

Abstract Concurrent sampling of PM2.5 aerosol at a roadside of heavy traffic (1.2 m above ground) and on a nearby rooftop (50 m above ground) was conducted at a same location in urban Guangzhou in September, October 2006 and January 2007. The samples were analyzed for eighteen polycyclic aromatic hydrocarbons (PAHs), together with major aerosol constituents and certain organic tracers for vehicular emissions (hopanes) and biomass burning (levoglucosan). Elemental carbon (EC) and hopanes were observed to be lower by 21–38% and 28–84%, respectively, at the rooftop than the roadside, confirming vehicular emissions as a significant local PM source. On the other hand, sulfate showed little vertical gradient, consistent with its secondary origin and its regional characteristics. The roadside-rooftop sample pairs have provided an opportunity in evaluating relative contributions of vehicular emissions and regional sources to ambient PAHs in this urban location. Concentrations of the total PAHs were ∼43% lower at rooftop in the September 2006 samples while they were at similar levels between rooftop and roadside in the October 2006 and January 2007 samples. Sources of PAHs were investigated through comparing ambient data of PAH isomer pairs and PAH/EC ratios with relevant source profiles including those of Guangzhou roadway tunnel emissions, rice straw/sugarcane leave combustion, and industrial coal combustion. The 4-ring PAHs such as pyrene and fluoranthene had a shift in their dominating source from vehicular emissions in September and October to regional combustion source in January. A few major 5- and 6-ring PAHs such as benzo[ghi]perylene and indeno[1,2,3-cd]pyrene were likely heavily influenced by regional biomass burning emissions in all three sampling months. Benzo(a)pyrene-equivalent carcinogenic potency (BaPeq) was calculated to evaluate the cancer risk of carcinogenic PAHs on the public. BaPeq levels in PM2.5 were significantly higher at the roadside than those at the rooftop in September; however, levels of BaPeq at the rooftop were drastically elevated and became comparable to those at the roadside in October and January due to regional sources dominating the carcinogenic PAHs. This suggests that it is important to control regional combustion sources to reduce air pollution-related health risk in urban Guangzhou.

In-cloud oxalate formation in the global troposphere: a 3-D modeling study

Abstract. Organic acids attract increasing attention as contributors to atmospheric acidity, secondary organic aerosol mass and aerosol hygroscopicity. Oxalic acid is globally the most abundant dicarboxylic acid, formed via chemical oxidation of gas-phase precursors in the aqueous phase of aerosols and droplets. Its lifecycle and atmospheric global distribution remain highly uncertain and are the focus of this study. The first global spatial and temporal distribution of oxalate, simulated using a state-of-the-art aqueous-phase chemical scheme embedded within the global 3-dimensional chemistry/transport model TM4-ECPL, is here presented. The model accounts for comprehensive gas-phase chemistry and its coupling with major aerosol constituents (including secondary organic aerosol). Model results are consistent with ambient observations of oxalate at rural and remote locations (slope = 1.16 ± 0.14, r2 = 0.36, N = 114) and suggest that aqueous-phase chemistry contributes significantly to the global atmospheric burden of secondary organic aerosol. In TM4-ECPL most oxalate is formed in-cloud and less than 5 % is produced in aerosol water. About 62 % of the oxalate is removed via wet deposition, 30 % by in-cloud reaction with hydroxyl radical, 4 % by in-cloud reaction with nitrate radical and 4 % by dry deposition. The in-cloud global oxalate net chemical production is calculated to be about 21–37 Tg yr−1 with almost 79 % originating from biogenic hydrocarbons, mainly isoprene. This condensed phase net source of oxalate in conjunction with a global mean turnover time against deposition of about 5 days, maintain oxalate's global tropospheric burden of 0.2–0.3 Tg, i.e. 0.05–0.1 Tg-C that is about 5–9 % of model-calculated water soluble organic carbon burden.

Haze episodes at Syowa Station, coastal Antarctica: Where did they come from?

During our aerosol measurement program at Syowa Station, Antarctica, in 2004–2007, some low‐visibility (haze) phenomena were observed during winter–spring under conditions with low winds and without drifting snow and fog. During “Antarctic haze” phenomena, the number concentration of aerosol particles and black carbon concentration increased by 1 to 2 orders higher relative to background conditions at Syowa Station, whereas surface O3 concentration dropped simultaneously, especially after polar sunrise. Chemical analysis showed that major aerosol constituents in the haze phenomena were sea salt (e.g., Na+, Cl−). Trajectory analysis and the Navy Aerosol Analysis and Prediction System model showed that plumes from biomass burning in South America and southern Africa were transported to Syowa Station, on the Antarctic coast, because of the eastward (occasionally westward) approach of cyclones in the Southern Ocean and subsequent poleward flow. This poleward flow from midlatitudes of the plume and injection of sea‐salt particles during the transport might engender Antarctic haze phenomena at Syowa Station. Differences of O3 concentration between the background and the haze conditions tended to be larger in spring (after polar sunrise) than in winter. Enhancement of sea‐salt particles in the haze events can serve important roles in providing additional sources of reactive halogen species.

Composition profile of oxygenated organic compounds and inorganic ions in PM2.5 in Hong Kong

Environment context.Oxygenated organic compounds are active constituents in ambient aerosols, affecting their hygroscopic properties and other interactions with water. We have measured 29 oxygenated organic compounds, together with inorganic ions and other major aerosol constituents, in ambient samples collected under various synoptic conditions in Hong Kong. These composition profiles of water-soluble matter provide valuable data for modelling and theoretical studies of aerosol–water interactions. Abstract. This study reports a comprehensive dataset of oxygenated compounds, inorganic ions and other major aerosol constituents in fine particulate matter (2.5 μm) in the urban atmosphere of Hong Kong in periods of different synoptic weather conditions during 2003–05. The oxygenated compounds quantified include C2–C10 dicarboxylic acids, C3–C9 ketoacids and C2–C3 dicarbonyls, their combined concentrations accounting for 3.2–18.2% of water-soluble organic carbon on a carbon mass basis. Six C2 and C3 oxygenated compounds, namely oxalic acid, malonic acid, glyoxylic acid, pyruvic acid, glyoxal, and methyl glyoxal, dominate this suite of oxygenated compounds, accounting for 75% of the total quantified oxygenated species. Good correlations were observed among most of the quantified oxygenated compounds, suggesting that a relatively stable abundance distribution exists under varying synoptic conditions. These composition profiles provide a comprehensive dataset for use in modelling and theoretical studies of aerosol–water interactions, secondary aerosol formation pathways, and speciated organic mass distributions.

Abundance and size distribution of HULIS in ambient aerosols at a rural site in South China

HUmic-LIke Substances (HULIS) comprise a significant fraction of the water-soluble organic aerosol mass and influence the water uptake properties of aerosols in the atmosphere. In this work, the abundance and size distributions of HULIS in ambient aerosols were measured in a rural location in South China at a time with a visible presence of crop residue burning. PM 2.5 samples of fresh smoke from burning rice straw and sugar cane leaves were also collected and analyzed for HULIS and major aerosol constituents. HULIS were abundant in both ambient samples and in fresh biomass burning emissions, accounting for ∼60% of the water-soluble organic carbon in the ambient aerosols and ∼30% in the fresh biomass burning aerosols. In the particles in the range of 0.32–1.8 μm, the abundance of HULIS was 40–90% of the combined abundance of sulfate and ammonium, suggesting that HULIS should be considered when quantifying the role of sulfate aerosols serving as cloud condensation nuclei. The size distribution of HULIS was characterized by a dominant droplet mode with a mass median aerodynamic diameter (MMAD) in the range of 0.63–0.87 μm, accounting for 81% of the total HULIS mass, a minor condensation mode (12%, MMAD: 0.23–0.28 μm) and a coarse mode (7%, MMAD: 4.0–5.7 μm). The small amount of HULIS in the coarse mode indicated that soil-derived HULIS was a very minor source. On the basis of the size distribution characteristics, HULIS were postulated to have multiple sources, including secondary formation in cloud droplets, secondary formation through heterogeneous reactions or aerosol-phase reactions, and primary emissions from biomass burning.

Internally mixed soot, sulfates, and organic matter in aerosol particles from Mexico City

Abstract. Soot particles, which are aggregated carbonaceous spherules with graphitic structures, are major aerosol constituents that result from burning of fossil fuel, biofuel, and biomass. Their properties commonly change through reaction with other particles or gases, resulting in complex internal mixtures. Using a transmission electron microscope (TEM) for both imaging and chemical analysis, we measured ~8000 particles (25 samples) with aerodynamic diameters from 0.05 to 0.3 μm that were collected in March 2006 from aircraft over Mexico City (MC) and adjacent areas. Most particles are coated, consist of aggregates, or both. For example, almost all analyzed particles contain S and 70% also contain K, suggesting coagulation and condensation of sulfates and particles derived from biomass and biofuel burning. In the MC plumes, over half of all particles contained soot coated by organic matter and sulfates. The median value of the soot volume fraction in such coated particles is about 15%. In contrast to the assumptions used in many climate models, the soot particles did not become compact even when coated. Moreover, about 80% by volume of the particles consisting of organic matter with sulfate also contained soot, indicating the important role of soot in the formation of secondary aerosol particles. Coatings on soot particles can amplify their light absorption, and coagulation with sulfates changes their hygroscopic properties, resulting in shorter lifetimes. Through changes in their optical and hygroscopic properties, internally mixed soot particles have a greater effect on the regional climate of MC than uncoated soot particles.

Case study of Raman lidar measurements of Asian dust events in 2000 and 2001 at Nagoya and Tsukuba, Japan

Vertical distributions of aerosol optical properties and relative humidity were measured with a Raman lidar at Nagoya and Tsukuba, Japan, during the Asian dust events in 2000 and 2001. The data obtained on 23 April 2001 showed a maximum of aerosol backscattering ratio ( R) of 3.5–4.0 at 532 nm at an altitude of 5 km over both measurement sites. Around that height the aerosol depolarization ratios ( δ a), which indicate the aerosol nonsphericity, were higher than 20% and the relative humidities (RH) were lower than 30%. The aerosol optical thickness between 4 and 7 km was 0.18±0.02 and the average aerosol extinction-to-backscatter ratio (lidar ratio) was 46±5 sr at Tsukuba. This aerosol layer was present for over 6 h and finally showed the highest δ a value of about 33% and the lidar ratio of 10±3 sr at the uppermost region, where the RH was almost saturated with respect to ice. The data obtained on 4 May 2000 at Nagoya showed relatively high R values (∼2.5) below 5 km . The values of δ a were higher than 15% between 3.5 and 8 km in which the maximum RH was about 60%. The values of δ a and RH showed a weak negative correlation below 3.5 km , where the RH varied between 30% and 70%. In the 5– 8 km region, the δ a values were correlated negatively with the wavelength exponent of the aerosol backscattering coefficient ( α), whereas they showed the lowest value (∼7%) at smaller α values (<0) in the 2– 5 km region. We hypothesized that these relations of δ a to α and RH are due to the mixing state of mineral dust, sea-salt, and sulfate-containing particles that are major aerosol constituents in the free troposphere during the Asian dust period and to the dependence of their shape and size on RH.

Identification of source region profiles by the chemical composition ofsuspended particulates imported into Berlin (W)

Atmospheric aerosols were collected for one year and analyzed for its chemical constituents. Detailed masscompositions were determined for each particle size range (FPM, CPM, PM10) and for six distinct source regions, allocated by relating the aerosol samples with trajectory directions. An intercomparison of regional aerosol profiles provides additional information about trace elements and major aerosol constituents of the source regions.