Long-term (2001-2013) observations of water-soluble dicarboxylic acids and related compounds over the western North Pacific: trends, seasonality and source apportionment

To better understand the impact of East Asian pollutants on the molecular composition of marine organic aerosols, we conducted long-term (2001-2013) observations of water-soluble dicarboxylic acids and related compounds in total suspended particulate samples collected at Chichijima Island in the western North Pacific (WNP). Seasonal variations of all the diacids and related compounds showed maxima in winter and spring and minima in summer, except for azelaic acid (C-9), which maximized in summer to autumn. The overall annual concentrations of the total diacids,omega-oxoacids and a-dicarbonyls showed an increase during 2001-2013. We found a significant (p 0.05) acids, and methylglyoxal (MeGly). In contrast, phthalic acid (p < 0.05) and glyoxal (Gly) showed a decrease in their trends. We also found a significant decrease in the trend of the Gly/MeGly mass ratios. These results demonstrate that the enhanced concentrations of diacids over the WNP are majorly attributed to the aqueousphase photooxidation of biogenic volatile organic compounds from East Asia followed by long-range atmospheric transport. Further, positive matrix factorization analysis showed a biogenic photochemical contribution (42%) was the dominant source of oxalic acid in the WNP

Long-term (2001-2012) trends of carbonaceous aerosols from a remote island in the western North Pacific: an outflow region of Asian pollutants

The present study reports on long-term trends of carbonaceous aerosols in total suspended particulate (TSP) samples collected at Chichijima in the western North Pacific during 2001-2012. Seasonal variations of elemental carbon (EC), organic carbon (OC), and water-soluble organic carbon (WSOC) concentrations showed maxima in winter to spring and minima in summer. These seasonal differences in the concentrations of carbonaceous aerosols were associated with the outflows of polluted air masses from East Asia, which are clearly distinguishable from pristine air masses from the central Pacific. The higher concentrations of carbonaceous aerosols during winter to spring are associated with long-range atmospheric transport of East Asian continental polluted air masses, whereas lower concentrations may be due to pristine air masses from the central Pacific in summer. The annual trends of OC/EC (+0.46% yr(-1)), WSOC (+0.18% yr(-1)) and WSOC/OC (+0.08% yr(-1) showed significant (p < 0.05) increases during the period of 2001-2012, suggesting that photochemical formation of WSOC and its contributions to secondary organic aerosols (SOAs) have increased over the western North Pacific via long-range atmospheric transport. We found a significant increase (+0.33% yr(-1))in nss-K+/EC ratios, demonstrating that concentrations of biomass-burning-derived carbonaceous aerosols have increased, while those of primary fossilfuel-derived aerosols have decreased over the western North Pacific. Further, secondary biogenic emissions are also important over the western North Pacific as inferred from a significant increase (+0.14% yr(-1))in the concentrations of methanesulfonate (MSA(-), a tracer for biogenic sources). This point was further supported by a moderate correlation (r = 0.40) between WSOC and MSA. We also found a significant increase in OC/TC (total carbon) and WSOC/TC ratios, further suggesting that photochemical formation of WSOC and its contributions to SOAs have increased over the western North Pacific during 2001-2012 via long-range atmospheric transport from East Asia

Effects of chemical composition and mixing state on size-resolved hygroscopicity and cloud condensation nuclei activity of submicron aerosols at a suburban site in northern Japan in summer

Ambient hygroscopic properties, numbers of size-segregated cloud condensation nuclei (CCN) at different supersaturations (0.1%-0.8%), and the chemical composition of submicron particles were simultaneously measured at a suburban site in northern Japan in summer. Two distinct periods with different growth factors (GF), CCN activation diameters, and chemical compositions were observed. The data suggest that internally mixed sulfate aerosols dominated the accumulation size mode in relatively aged aerosols during the first period, whereas particles observed during the latter periods showed external mixing dominated by organics, which was linked to low hygroscopicity and CCN activity. In particular, the higher loading of water-soluble organic matter (WSOM; similar to 60% of OM by mass) with increased WSOM/sulfate ratios corresponded to a low hygroscopicity parameter derived from the CCN measurement (kappa(CCN) = 0.15 +/- 0.02) at a dry diameter (D-dry) of 146 nm. The results suggest that WSOM, likely dominated by the influence of biogenic sources, contributed to reducing the hygroscopicity and CCN activation at this particle size. Temporal variations in the number concentrations for low GF mode at D-dry = 49.6 nm were similar to those in the elemental carbon (EC) concentration, suggesting that EC contributed to reducing hygroscopicity at this smaller size. Our results suggest that chemical composition and mixing state are important factors controlling the hygroscopicity and CCN activation of submicron particles. These results provide useful data sets of size-resolved subsaturated and supersaturated hygroscopicity and highlight the importance of the abundance of OM relative to sulfate in predicting the effects on climate change

Impact of ice-free oases on particulate matter over the East Antarctic: Inferences from the carbonaceous, water-soluble species and trace metals

The present study reports on carbonaceous, water-soluble species and trace metals in PM 10 aerosols collected at Bharati station during the austral summer (December 17, 2016 to February 2, 2017) over East Antarctica. Organic matter was the predominant among all measured species followed by nss-Ca 2þ and nss-SO 4 2-. Two distinct air masses that arrive from high-altitude-troposphere (HTAs) and low-altitude-troposphere (LTAs) regions which clearly showed significant differences in concentrations of measured chemical and metal species as inferred from the air mass backward trajectory analysis and mixed layer height variations. Based on significant positive correlations among chemical species, aerosol liquid water content (ALWC), and PM 10 mass, we confirmed that the aqueous-phase formation of secondary aerosols followed by atmospheric processing are possible sources in HTAs while primary emissions associated with soil/dust from ice-free regions and in-situ emissions are major sources in LTAs. This result further supported by significant (p < 0.05) higher concentrations of specific trace metals (for example, Fe, Ti, and Pb) in LTAs. Moreover, higher cation-to-anion (Σ þ /Σ À) ratios suggesting the alkaline nature of aerosols at Bharati. The present study demonstrates that ice-free regions over East Antarctica may act as major sources of particulate matter, thus significant implications toward climate change over the global environment