One-year observations of carbonaceous and nitrogenous components and major ions in the aerosols from subtropical Okinawa Island, an outflow region of Asian dusts

Abstract

Ambient aerosol samples (TSP, <i>n</i>=50), collected at subtropical Okinawa Island, Japan, an outflow region of Asian dusts in the western North Pacific, were studied for organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), water-soluble total nitrogen (WSTN), water-soluble organic nitrogen (WSON) and major ions to better understand the long-range atmospheric transport and formation and transformation pathways of East Asian aerosols. Concentrations of OC, EC, WSOC, WSTN and WSON ranged from 0.76 to 7.1 &mu;g m^&minus;3 (av. 1.74 ± 1.03 &mu;g m^&minus;3), 0.07–0.96 &mu;g m^&minus;3 (0.28 ± 0.19 &mu;g m^&minus;3), 0.27–1.9 &mu;g m^&minus;3 (0.73 ± 0.38 &mu;g m^&minus;3), 0.77 to 3.03 &mu;g m^&minus;3 (0.58 ± 0.46 &mu;g m^&minus;3) and 0 to 2.2 &mu;g m^&minus;3 (0.12 ± 0.23 &mu;g m^&minus;3), respectively. The average concentration of OC is higher in growing seasons; spring (2.36 &mu;g m^&minus;3) and summer (1.79 &mu;g m^&minus;3). Similarly, the highest concentrations of EC and WSOC were found in spring (av. 0.41 &mu;g m^&minus;3 and 0.95 &mu;g m^&minus;3, respectively) followed by winter (0.37 and 0.90 &mu;g m^&minus;3) whereas the lowest concentrations were found in summer (0.19 and 0.52 &mu;g m^&minus;3, respectively). In contrast, higher concentrations of WSTN were observed in winter (0.86 &mu;g m^&minus;3) and lower concentrations were observed in summer (0.37 &mu;g m^&minus;3) and autumn (0.34 &mu;g m^&minus;3). Similarly, higher concentrations of WSON were observed in early summer (av. 0.26 &mu;g m^&minus;3) due to the emission from marine biota. The high OC/EC (av. 7.6) and WSOC/OC (44%) ratios suggest the secondary formation of organic aerosols. The OC/EC ratios, correlation analyses between OC and EC (<i>r</i> = 0.81), and OC and MSA^- (0.81) in spring suggest that springtime aerosols are influenced by additional marine and terrestrial biogenic sources. The correlation analyses of Ca²⁺ and TSP in spring suggests a significant influence from dust whereas the higher concentrations of NO₃^&minus; and nss-SO₄^2&minus; in winter suggest the influence from anthropogenic sources including biomass burning, vehicular emission and coal combustion. NH₄-N/WSTN ratios peaked in winter (0.56), indicating an important contribution of biomass burning to WSTN in cold season. In contrast, higher NO₃-N/WSTN ratio in spring than winter suggests that vehicular emissions are significant in spring. Correlation analyses of major ions suggest that NH₄⁺ and Ca²⁺ play major role in the neutralization of aerosols forming NH₄HSO₄, (NH₄)₂SO₄ and CaSO₄

Size-resolved aerosol chemical analysis of extreme haze pollution events during early 2013 in urban Beijing, China

“…The size distributions of Ca 2+ and Mg 2+ were different than those observed in previous haze pollution events in Beijing, which showed that the distribution of these species primarily peaked in the coarse mode [29]. This difference might be due to the high acidity of fine particles on HP days, which improves the solubility of calcium and magnesium [50]. Ca 2+ , Mg 2+ , Na + , Na, Cr and V also exhibited similar concentration variations and may represent dust sources, including road surface dust and dust from long-range transport.…”

Water-Soluble Organic Nitrogen in High Mountain Snow Samples from Central Japan

“…Wang et al (2013) also reported high WSON/WSTN ratio of 76 % in dusty aerosol samples from a semi-arid region in central China (dust storm period). In contrast, WSON/WSTN ratio in aerosol samples from Okinawa Island, Japan, an outflow region of Asian dust, was about 14% (Kunwar and Kawamura, 2014). We found that WSON does not comprise of major fraction of WSTN in the Japanese high mountain snow samples.…”

Biomass burning contributions to urban PM_2.5 along the coastal lines of southeastern China

“…Using ECtracer method, however, Kunwar and Kawamura (2014) found lower SOC to WSOC ratios in winter-spring (0.49Á 0.78) but higher ratios in summer-fall (1.53Á1.65) on Okinawa Island. Ding et al (2012) has pointed out the significant overestimation of SOC by EC-tracer method, which could result in the higher amount of SOC with respect to WSOC throughout the sampling campaigns in this study.…”