Lujie Ren

Fluorescent water-soluble organic aerosols in the High Arctic atmosphere

Organic aerosols are ubiquitous in the earth’s atmosphere. They have been extensively studied in urban, rural and marine environments. However, little is known about the fluorescence properties of water-soluble organic carbon (WSOC) or their transport to and distribution in the polar regions. Here, we present evidence that fluorescent WSOC is a substantial component of High Arctic aerosols. The ratios of fluorescence intensity of protein-like peak to humic-like peak generally increased from dark winter to early summer, indicating an enhanced contribution of protein-like organics from the ocean to Arctic aerosols after the polar sunrise. Such a seasonal pattern is in agreement with an increase of stable carbon isotope ratios of total carbon (δ13CTC) from −26.8‰ to −22.5‰. Our results suggest that Arctic aerosols are derived from a combination of the long-range transport of terrestrial organics and local sea-to-air emission of marine organics, with an estimated contribution from the latter of 8.7–77% (mean 45%).

Molecular distributions and compound-specific stable carbon isotopic compositions of lipids in wintertime aerosols from Beijing.

Molecular distributions and stable carbon isotopic compositions (δ13C) of n-alkanes, fatty acids and n-alcohols were investigated in urban aerosols from Beijing, northern China to better understand the sources and long-range atmospheric transport of terrestrial organic matter during polluted and clear days in winter. n-Alkanes (C19–C36), fatty acids (C8–C32) and n-alcohols (C16–C32) detected in Beijing aerosols are characterized by the predominance of C23, C16 and C28, respectively. Carbon preference index (CPI) values of n-alkanes, the ratios of the sum of odd-numbered n-alkanes to the sum of even-numbered n-alkanes, are close to 1, indicating a heavy influence of fossil fuel combustion. Relatively higher ratios of C(18:0+16:0)/C(18:n+16:1) (fatty acids) on clear days than polluted days indicate that long-distance transport and/or photochemical aging are more significant during clear days. δ13C values of n-alkanes and low molecular weight fatty acids (C16:0, C18:0) ranged from –34.1 to −24.7% and −26.9 to −24.6%, respectively, which are generally heavier on polluted days than those on clear days. Such a wide range suggests that atmospheric lipids in Beijing aerosols originate from multiple sources and encounter complicated atmospheric processes during long-range transport in North China.

High Contribution of Nonfossil Sources to Submicrometer Organic Aerosols in Beijing, China

Source apportionment of organic carbon (OC) and elemental carbon (EC) from PM1 (particulate matter with a diameter equal to or smaller than 1 μm) in Beijing, China was carried out using radiocarbon (14C) measurement. Despite a dominant fossil-fuel contribution to EC due to large emissions from traffic and coal combustion, nonfossil sources are dominant contributors of OC in Beijing throughout the year except during the winter. Primary emission was the most important contributor to fossil-fuel derived OC for all seasons. A clear seasonal trend was found for biomass-burning contribution to OC with the highest in autumn and spring, followed by winter and summer. 14C results were also integrated with those from positive matrix factorization (PMF) of organic aerosols from aerosol mass spectrometer (AMS) measurements during winter and spring. The results suggest that the fossil-derived primary OC was dominated by coal combustion emissions whereas secondary OC was mostly from fossil-fuel emissions. Taken together with previous 14C studies in Asia, Europe and USA, a ubiquity and dominance of nonfossil contribution to OC aerosols is identified not only in rural/background/remote regions but also in urban regions, which may be explained by cooking contributions, regional transportation or local emissions of seasonal-dependent biomass burning emission. In addition, biogenic and biomass burning derived SOA may be further enhanced by unresolved atmospheric processes.

Primary biogenic and anthropogenic sources of organic aerosols in Beijing, China: Insights from saccharides and n-alkanes

Sugars and n-alkanes are important organic constituents of atmospheric fine particulate matter (PM2.5). For better understanding their sources and seasonal variations in urban atmosphere, sugar compounds (anhydrosugars, sugars and sugar alcohols) and homologue n-alkanes (C18-C37) were studied in PM2.5 samples collected from September 2013 to July 2014 in Beijing, China. In general, all measured compounds showed the lowest levels in summer. Higher concentrations of sugar compounds and n-alkanes were observed in winter, probably due to elevated combustion emissions (e.g., coal, biofuel and agricultural residue burning) and stable meteorological conditions during heating season. Levoglucosan was the major sugar species in all seasons particularly in autumn and winter, highlighting the significant contribution of biomass burning to fine organic aerosols throughout the whole year especially in cold seasons. Plant waxes contributed to n-alkanes the most in late spring (54.5%) and the least in winter (11.6%); while fossil fuel combustion had the largest contribution in winter (385 ng m-3). The weak odd-carbon predominance of n-alkanes in wintertime aerosols also suggests fossil fuel combustion as the important source of organic aerosols in the heating season. Soil resuspension, fossil fuel combustion and biomass burning, and secondary sources are the main sources of OC in PM2.5 at Beijing. The seasonal variation in source contributions indicates that meteorological condition is a key factor in controlling PM2.5 levels. Furthermore, dust storms in spring can strongly enhance the atmospheric level of fine organic matter in Beijing.

The organic molecular composition, diurnal variation, and stable carbon isotope ratios of PM2.5 in Beijing during the 2014 APEC summit

Organic tracers are useful for investigating the sources of carbonaceous aerosols but there are still no adequate studies in China. To obtain insights into the diurnal variations, properties, and the influence of regional emission controls on carbonaceous aerosols in Beijing, day-/nighttime PM2.5 samples were collected before (Oct. 15th - Nov. 2nd) and during (Nov. 3rd - Nov. 12th) the 2014 Asia-Pacific Economic Cooperation (APEC) summit. Eleven organic compound classes were analysed using gas chromatography/mass spectrometry (GC/MS). In addition, the stable carbon isotope ratios (δ13CTC) of total carbon (TC) were detected using an elemental analyser/isotope ratio mass spectrometry (EA/irMS). Most of the organic compounds were more abundant during the night than in the daytime, and their concentrations generally decreased during the APEC. These features were associated with the strict regional emission controls and meteorological conditions. The day/night variations of δ13CTC were smaller during the APEC than those before the APEC the summit, suggesting that regionally transported aerosols are potentially played an important role in the loading of organic aerosols in Beijing before the APEC summit. The source apportionment based on the organic tracers suggested that biomass burning, plastic and microbial emissions, and fossil fuel combustion were important sources of organic aerosols in Beijing. Furthermore, a similar contribution of biomass burning to OC before and during the APEC suggests biomass burning was a persistent contributor to PM2.5 in Beijing and its surroundings.

Characterization of biogenic primary and secondary organic aerosols in the marine atmosphere over the East China Sea

Molecular composition and abundance of sugars and secondary organic aerosols (SOA) from biogenic sources over the East China Sea were investigated based on gas chromatography–mass spectrometry. Biogenic SOA tracers and sugars exhibit higher levels in the samples affected by continental air masses, demonstrating the terrestrial outflows of organic matter to the East China Sea. Glucose was the dominant sugar species (0.31–209, 18.8 ng m−3), followed by mannitol – a fungal spore tracer. All sugar compounds show generally higher average concentrations in the nighttime than in the daytime. 3-Methyl-1,2,3butanetricarboxylic acid, one higher generation photooxidation tracer of monoterpene SOA, was found to be the most abundant species among measured biogenic SOA markers, suggesting the input of aged organic aerosols through longrange transport. Fungal-spore-derived organic carbon (OC) was the biggest contributor to total OC (0.03 %–19.8 %, 3.1 %), followed by sesquiterpene-derived secondary OC (SOC), biomass-burning-derived OC, and monoterpeneand isoprene-derived SOC. Larger carbon percentages of biogenic primary OCs and SOCs in total OC presented in the terrestrially influenced aerosols indicate significant contributions of continental aerosols through long-range transport. Positive matrix factorization results illustrate that the secondary nitrate and biogenic SOA, biomass burning, and fungal spores were the main sources of OC in marine aerosols over the East China Sea, again highlighting the importance of the Asian continent as a natural emitter of biogenic organic aerosols together with anthropogenic aerosols over the coastal marine atmosphere.