Characteristics, seasonality and sources of inorganic ions and trace metals in North-east Asian aerosols

Abstract

Environmental context Atmospheric aerosols affect the Earth's climate system and can cause adverse effects on human health depending on their loading and chemical composition. This study presents the chemical characteristics and seasonality of inorganic ions and trace metals in atmospheric aerosols from Sapporo, northern Japan, and explores their possible sources. The work is relevant for our understanding of atmospheric composition and climate change. Abstract To better understand the characteristics, seasonality and sources of inorganic aerosols in North-east Asia, we studied total suspended particulate samples collected in Sapporo, northern Japan for inorganic ions and trace metals over a 1-year period. SO42- was found as the most abundant ionic species, which accounted for on average 43 +/- 15% of the measured total ionic mass followed by Cl-approximate to NO3-approximate to Na+. Among the metals determined, Ca was found as the most abundant (45 +/- 5.2% of the measured total metals) followed by Fe. Temporal variations of methanesulfonate (MS-) and SO42- showed a clear seasonal pattern with a maximum in summer followed by spring. Cl-, NO3-, NH4+ and K+ showed increasing trends from mid autumn to winter. Na+, Ca2+ and Mg2+ and crustal metals (Al, Ca, Fe, Ti and Mn) peaked in early spring. Na+ and Mg2+ and Ni, Cu and As were abundant in autumn whereas Zn was in spring. However, Cd and Pb did not show any seasonality. Based on comparisons of such seasonal trends with those of organic tracers as well as the air mass trajectories, we infer that the seasonality in inorganic aerosols in the North-east Asian atmosphere is mainly controlled by their season-specific source(s): soil dust in early spring, biogenic emissions in spring-summer, microbial activities in autumn and forest fires and biomass burning in autumn-winter. However, contributions from anthropogenic sources are significant in all seasons. This study also suggests that fungal spores partly contribute to some trace metals (i.e. Ni, Cu and As) whereas pollen contributes to Zn in aerosols

Atmospheric chemistry of nitrogenous aerosols in northeastern Asia: biological sources and secondary formation

“…Because the contribution of modern carbon from local vegetation is unlikely in winter, such an increase in pMC during winter has been mainly attributed to the contributions of biomass burning aerosols via long-range transport from eastern Asia (Pavuluri et al, 2013). In addition, temporal variations in crustal metals, e.g., Al, Ca and Fe, in Sapporo aerosols are consistent with those of TSP from winter to midsummer, with a peak in early spring, indicating a significant atmospheric transport of Asian dust from arid regions in Mongolia and China (Pavuluri et al, 2015). Therefore, we consider that the Sapporo aerosols were probably mainly influenced by air masses from distant sources that were transported a long way over northeastern Asia.…”

“…Since the sampling time is long (∼ 2 weeks) in this study, the evaporative loss from the particles should be more significant than the adsorbed gases by quartz fiber filter and thus the reported concentrations may be underestimated. However, the ambient temperatures encountered in Sapporo are rather low (range of averages of each sample period: −3.30 to 24.5 • C) (Pavuluri et al, 2015), and thus may not cause a significant evaporative loss of N species during the sampling period because quartz filters show a good retention for semivolatile NH 4 NO 3 sampled at an air temperature up to 21 • C and ∼ 30 % at even an elevated air temperature of 35 • C (Schaap et al, 2004). Therefore, we believe that our sampling technique does not have serious sampling artifacts even in summer.…”

“…In addition, the higher end (maximum 288 ng m Concentrations of isoprene-SOA tracers are the sum of the concentrations of 2-methylglyceric acid, cis-2-methyl-1,3,4-trihydroxy-1-butene, 3-methyl-2,3,4-trihydroxy-1-butene, trans-2-methyl-1,3,4-trihydroxy-1-butene, 2-methylthreitol and 2-methylerythritol, whereas concentrations of α-pinene-SOA tracers are the sum of the concentrations of 3-hydroxyglutaric, pinonic, pinic and 3-methyl-1,2,3-butanetricarboxylic acids. The data of organic molecular tracers are from Pavuluri et al (2013) and MSA − is from Pavuluri et al (2015).…”

“…Details of the measurements of inorganic ionic species such as NO − 3 , NH + 4 and methanesulfonate (MSA − , CH 3 SO − 3 ) are described elsewhere (Pavuluri et al, 2015). Briefly, an aliquot of filter sample was extracted with Milli Q water under ultrasonication and filtrated with a syringe filter (GL Sciences Chromatodisc Type A, 0.45 µm).…”

“…Amounts of inorganic N (IN), i.e., the sum of NO (Pavuluri et al, 2015). The amounts of ON, WSON and WION were estimated by the following equations (Miyazaki et al, 2011):…”