Explore the vast range of titles available.

Organic aerosols (OA) were studied in Fresno, California, in winter 2010 with an Aerodyne High Resolution Time‐of‐Flight Aerosol Mass Spectrometer (HR‐ToF‐AMS). OA dominated the submicron aerosol mass (average = 67%) with an average concentration of 7.9μg m−3 and a nominal formula of C1H1.59N0.014O0.27S0.00008, which corresponds to an average organic mass‐to‐carbon ratio of 1.50. Three primary OA (POA) factors and one oxygenated OA factor (OOA) representative of secondary OA (SOA) were identified via Positive Matrix Factorization of the high‐resolution mass spectra. The three POA factors, which include a traffic‐related hydrocarbon‐like OA (HOA), a cooking OA (COA), and a biomass burning OA (BBOA) released from residential heating, accounted for an average 57% of the OA mass and up to 80% between 6 – 9 P.M., during which enhanced emissions from evening rush hour traffic, dinner cooking, and residential wood burning were exacerbated by low mixed layer height. The mass‐based size distributions of the OA factors were estimated based on multilinear analysis of the size‐resolved mass spectra of organics. Both HOA and BBOA peaked at ∼140 nm in vacuum aerodynamic diameter (Dva) while OOA peaked at an accumulation mode of ∼460 nm. COA exhibited a unique size distribution with two size modes centering at ∼200 nm and 450 nm respectively. This study highlights the leading roles played by anthropogenic POA emissions, primarily from traffic, cooking and residential heating, in aerosol pollution in Fresno in wintertime. Key Points POA was emitted by three main sources: traffic, cooking, and residential heating POA dominated aerosol composition, especially in ultrafine particles SOA elevated at night, likely influenced by aqueous‐phase processing

Exploring secondary organic aerosol (SOA) processes is crucial for understanding climate and air pollution in megacities. This study introduces a new method using positive matrix factorization (PMF) to investigate the SOA process by integrating the OA and associated ions previously misidentified as inorganic aerosol in high-resolution aerosol mass spectrometry data. The mass spectra and time series of primary OA (POA) and less oxidized oxygenated OA (OOA) identified by this new method resembled those resolved by traditional PMF. However, more oxidized OOA (MO-OOA) identified by traditional PMF can be further subdivided into multiple OA factors, including nitrogen-enriched OA (ON-OA) and sulfur-enriched OA (OS-OA) in summer, and ON-OA, OS-OA, and OOA in winter. Our findings highlight the significant role of photochemical processes in the formation of OS-OA compared to ON-OA. The compositions of reconstructed MO-OOA varied under different O x (= O 3 + NO 2 ) and relative humidity conditions, emphasizing the limitations of using a constant mass spectrum. Aged biomass burning OA (BBOA) and coal combustion OA (CCOA), previously misattributed as POA, contributed 9.2% (0.43 µg m −3 ) and 7.0% (0.33 µg m −3 ) to SOA, respectively. Aged BBOA was more prone to forming OS-OA, whereas ON-OA showed higher correlations with aged CCOA, indicating distinct molecular compositions of SOA from different aged POA sources. Compared to aged BBOA, aged CCOA was more subject to conversion during aqueous phase processing. These results suggest that the variations in mass spectra and compositions need to be considered when simulating SOA processes.

To better understand precursors of dicarboxylic acids in ambient secondary organic aerosol (SOA), we studied C4–C9 dicarboxylic acids present in SOA formed from the oxidation of toluene, naphthalene, α-pinene, and isoprene. C4–C9 dicarboxylic acids present in SOA were analyzed by offline derivatization gas chromatography–mass spectrometry. We revealed that C4 dicarboxylic acids including succinic acid, maleic acid, fumaric acid, malic acid, DL-tartaric acid, and meso-tartaric acid are produced by the photooxidation of toluene. Since meso-tartaric acid barely occurs in nature, it is a potential aerosol tracer of photochemical reaction products. In SOA particles from toluene, we also detected a compound and its isomer with similar mass spectra to methyltartaric acid standard; the compound and the isomer are tentatively identified as 2,3-dihydroxypentanedioic acid isomers. The ratio of detected C4–C5 dicarboxylic acids to total toluene SOA mass had no significant dependence on the initial VOC/NOx condition. Trace levels of maleic acid and fumaric acid were detected during the photooxidation of naphthalene. Malic acid was produced from the oxidation of α-pinene and isoprene. A trace amount of succinic acid was detected in the SOA produced from the oxidation of isoprene.

Secondary organic aerosol (SOA) generated from the oxidation of organic gases are ubiquitous in the atmosphere, but their interaction with water vapor and their ice cloud formation potential at low temperatures remains highly uncertain. We report on onset conditions of water uptake and ice nucleation by amorphous SOA particles generated from the oxidation of naphthalene with OH radicals. Water uptake above 230 K was governed by the oxidation level of the SOA particles expressed as oxygen‐to‐carbon (O/C) ratio, followed by moisture‐induced phase transitions and immersion freezing. For temperatures from 200 to 230 K, SOA particles nucleated ice via deposition mode from supersaturated water vapor independent of O/C ratio at relative humidity with respect to ice (RHice) ∼10–15% below homogeneous ice nucleation limits. The glass transition temperature (Tg) for the amorphous SOA particles was derived as a function of two parameters: (1) relative humidity (RH) with respect to water and (2) oxidation level of the SOA. The data show that particle phase and viscosity govern the particles' response to temperature and RHand provide a straightforward interpretation for the observed different heterogeneous ice nucleation pathways and water uptake by the laboratory‐generated SOA and field‐collected particles. Since SOA particles undergo glass transitions, these observations suggest that atmospheric SOA are potentially important for ice cloud formation and climate. Key Points Amorphous secondary organic aerosol can act as efficient atmospheric ice nuclei Water uptake and ice nucleation are governed by glass transition points Glass transition points relevant for secondary organic aerosol are derived

The Meteorological Synthesizing Centre-West (MSC-W) of the European Monitoring and Evaluation Programme (EMEP) has been performing model calculations in support of the Convention on Long Range Transboundary Air Pollution (CLRTAP) for more than 30 years. The EMEP MSC-W chemical transport model is still one of the key tools within European air pollution policy assessments. Traditionally, the model has covered all of Europe with a resolution of about 50 km × 50 km, and extending vertically from ground level to the tropopause (100 hPa). The model has changed extensively over the last ten years, however, with flexible processing of chemical schemes, meteorological inputs, and with nesting capability: the code is now applied on scales ranging from local (ca. 5 km grid size) to global (with 1 degree resolution). The model is used to simulate photo-oxidants and both inorganic and organic aerosols. In 2008 the EMEP model was released for the first time as public domain code, along with all required input data for model runs for one year. The second release of the EMEP MSC-W model became available in mid 2011, and a new release is targeted for summer 2012. This publication is intended to document this third release of the EMEP MSC-W model. The model formulations are given, along with details of input data-sets which are used, and a brief background on some of the choices made in the formulation is presented. The model code itself is available at www.emep.int, along with the data required to run for a full year over Europe.

Organic molecular compositions of marine aerosol samples, collected at low latitudes to midlatitudes in the Northern Hemisphere during a round‐the‐world cruise, were studied using gas chromatography/mass spectrometry. More than 140 organic species were detected in the samples and were grouped into different compound classes based on the functionality and sources. The concentrations of total quantified organics ranged from 0.94 to 111 ng m−3 (average of 34 ng m−3). Biogenic secondary organic aerosol (SOA) tracers from the oxidation of isoprene (e.g., 2‐methyltetrols), α/β‐pinene (e.g., pinonic and pinic acids), and β‐caryophyllene (β‐caryophyllinic acid) were detected in all the samples. Their total concentrations ranged from 0.19 to 27 ng m−3, which account for 0.48–29% of the total identified organics and 0.05–1.5% of organic carbon in the marine aerosols. The spatial distributions of biogenic SOA tracers exhibited higher loadings over the coastal/tropical regions than the open oceans. In marine aerosols collected over the North Pacific and North Atlantic, the contributions of marine natural emissions (22–33%) were higher than those in the coastal regions (4–14%). Over the tropical regions, atmospheric oxidation products can account for 47–59% of the total organics, with biomass burning emissions of only 1–2%. However, over the western North Pacific, fossil fuel combustion (26%), atmospheric oxidation products (25%), and biomass burning (24%) were the main sources. This study indicates that long‐range atmospheric transport of continental aerosols and sea‐to‐air emission of marine organics, as well as atmospheric oxidation and/or photochemical aging, are important factors controlling the chemical composition of organic aerosols in the marine atmosphere. Key Points Marine organic aerosols were investigated at a molecular level Direct evidances were obtained for biogenic SOA tracers in the marine aerosols The source strengths are apportioned based on the identified organics

Atmospheric volatile organic compounds (VOCs) measurement was carried out using gas chromatography-flame ionization detector (GC-FID) technique (Airmo VOCs online analyzer) in a typical urban area in Beijing from April 2014 to January 2015. Ambient levels, variation characteristics and influential factors contributing to the formation of near-ground-ozone and secondary organic aerosols as well as health risk assessment of VOCs were analyzed. Based on these analyses, the important VOC species that should be given more attention for pollution control were identified and the source apportionment of VOCs was made. Suggestions for VOCs pollution control countermeasures were put forward. The annual average concentration of 84 VOCs was 119 μg·m−3 and the hourly mean concentration was 9.11–567 μg·m−3. Ambient level of VOCs in Beijing has been alleviated in recent years, but is still severe compared to some other cities. VOCs with the largest proportion were alkanes in spring and halogenated hydrocarbons in summer, autumn and winter. The variation of 84 VOCs concentrations was consistent with that of the ambient air quality index, indicating that VOCs had a strong influence on ambient air quality. Influenced by the concentration and activity of VOCs, the largest contribution to ozone formation potential and secondary organic aerosol formation potential came from alkenes and aromatic hydrocarbons, respectively. Five VOCs species such as benzene pose carcinogenic risk to exposed populations. Contrary to some previous studies, benzene was found to have potential cancer risk in some urban areas in China. The main sources of VOCs in the study area were vehicle exhaust, solvent usage, and industrial processes. In order to improve air quality in Beijing and reduce the infection rate of air pollutant related diseases, it is necessary to strengthen the control the emission of VOCs from those three sources.

Diesel vehicles are recognized as significant mobile sources of particulate matter emissions. As a renewable and environmentally friendly alternative to conventional fossil diesel, biodiesel offers the benefit of reducing greenhouse gas emissions. However, existing research on biodiesel emissions primarily focuses on primary emissions, with a limited understanding of their impact on secondary organic aerosol (SOA) formation. In this study, a diesel engine test bench was employed under idle conditions using three commonly used biodiesel blends. Exhaust emissions were directly introduced into the HAP-SWFU chamber, a quartz glass smog chamber designed to characterize both primary emissions and SOA formation during the photochemical oxidation process. The black carbon and primary organic aerosol (POA) emission factors for the three biodiesel blends under idle conditions ranged from 0.31 to 0.58 g kg−1 fuel and 0.99 to 1.06 g kg−1 fuel, respectively. The particle size of exhaust particulates peaked between 20 and 30 nm, and nucleation-idle conditions were found to be the dominating mode. The SOA production factor was between 0.92 and 1.15 g kg−1 fuel, and the SOA/POA ratio ranged from 1.35 to 2.37, with an average of 1.86. This study concludes that the POA emission factor for biodiesel under idle conditions is comparable to values reported in previous studies on pure diesel exhaust, with the maximum SOA production factor reduced by 38%.

Biomass burning is one of the major emitters of airborne particulate matter (PM) and gaseous mercury. In order to apply the isotopic fingerprinting method to process identification and source apportionment studies, isotopic characterizations of targeted substances at emission are indispensable. Here, we report the stable isotopic composition of total gaseous mercury (TGM) and the stable and radiocarbon isotopic composition of low-volatile water-soluble nitrogen (LV-WSN) and organic carbon (LV-WSOC) in PM emitted from open grass field burning in the Aso region of Japan. The measurement results showed that TGM concentrations in the air increased during the open field burning events, indicating the presence of TGM emissions. The results of LV-WSN analysis showed very low concentrations; therefore, the stable nitrogen isotope ratios could not be measured. The stable mercury isotope ratios exhibited lighter composition than those observed during non-biomass-burning days. The analysis of LV-WSOC revealed heavy stable carbon isotope ratios (average ± SD, −18 ± 2‰), suggesting a substantial contribution from C4 plant carbon. The 14C analysis showed that more than 98% of the LV-WSOC was modern carbon, indicating the contribution of plant carbon to PM emitted from biomass burning. The findings here provide reference isotope compositions of TGM and particulate LV-WSOC from biomass burning in this region.

To understand the influence of trans-boundary air pollution on the air quality of Fukuoka, the mass concentration and chemical composition of fine particulate matter (PM) were observed at urban (Fukuoka) and rural (Fukue Island) sites in the northern Kyushu area in Japan. Chemical composition was measured using an aerosol mass spectrometer. Organic aerosol (OA) data were analyzed by the positive matrix factorization (PMF) method. Sulfate and low-volatile oxygenated OA (LV-OOA) were dominant for all of the PM2.5 mass variations on Fukue Island, where the trans-boundary air pollution is dominant in the winter-spring season. In Fukuoka, however, sulfate accounted for the largest fraction of total chemical species under high PM2.5 mass concentrations (>35 µg·m−3), while organics and nitrate made up a large fraction under low PM2.5 (<10 µg·m−3). Under the high PM2.5 condition, LV-OOA was also dominant. This indicates that high PM2.5 mass concentrations were attributed to the long-range transport of air pollution. Although the trans-boundary air pollution prevails in the winter-spring season, high sulfate concentrations were observed in the summer of 2012. In addition to the volcanic activities and photochemical reactions, long-range, trans-boundary air pollutions are influential factors not only in winter-spring but also in summer.