Abstract. Biomass burning (BB) largely modifies the chemical composition of atmospheric aerosols on the globe. We collected aerosol samples (TSP) at Cape Hedo, on subtropical Okinawa Island, from October 2009 to February 2012 to study anhydrosugars as BB tracers. Levoglucosan was detected as the dominant anhydrosugar followed by its isomers, mannosan and galactosan. We found a clear seasonal trend of levoglucosan and mannosan with winter maxima and summer minima. Positive correlation was found between levoglucosan and nss-K+ (r = 0.38, p < 0.001); the latter is another BB tracer. The analyses of air mass trajectories and fire spots demonstrated that the seasonal variations of anhydrosugars are caused by long-range transport of BB emissions from the Asian continent. We found winter maxima of anhydrosugars, which may be associated with open burning and domestic heating and cooking in northern and northeastern China, Mongolia and Russia and with the enhanced westerly winds. The monthly averaged levoglucosan / mannosan ratios were lower (2.1–4.8) in May–June and higher (13.3–13.9) in November–December. The lower values may be associated with softwood burning in northern China, Korea and southwestern Japan whereas the higher values are probably caused by agricultural waste burning of maize straw in the North China Plain. Anhydrosugars comprised 0.22% of water-soluble organic carbon (WSOC) and 0.13% of organic carbon (OC). The highest values to WSOC (0.37%) and OC (0.25%) were found in winter, again indicating an important BB contribution to Okinawa aerosols in winter. This study provides useful information to better understand the effect of East Asian biomass burning on the air quality in the western North Pacific Rim.

Abstract. Ambient aerosol samples (TSP, n = 50) were collected for 12 months at subtropical Okinawa Island, Japan, an outflow region of Asian dusts in the western North Pacific and analysed 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 formation and transformation of East Asian aerosols during long-range atmospheric transport. Concentration ranges of these components are; OC: 0.76-7.1 µg m −3 (av. and Ca 2+ play major role in the neutralization of acidic aerosols forming NH 4 HSO 4 , (NH 4 ) 2 SO 4 and CaSO 4 .

Primary biological aerosol particles (PBAPs) play an important role in affecting atmospheric physical and chemical properties. Aerosol samples were collected at Cape Hedo, Okinawa Island, Japan, from October 2009 to February 2012 and analyzed for five primary saccharides and four sugar alcohols as PBAP tracers. We detected high levels of sucrose in spring when blossoming of plants happens and prolifically emits pollen to the air. Concentrations of glucose, fructose, and trehalose showed levels higher than the other saccharides in spring in 2010. In comparison, primary saccharide levels were mutually comparable in spring, summer, and autumn in 2011, indicating the interannual variability of their local production in subtropical forests, which is driven by local temperature and radiation. High trehalose events were found to be associated with Asian dust outflows, indicating that Asian dust also contributes to PBAPs at Okinawa. Sugar alcohols peaked in summer and correlated with local precipitation and temperature, indicating high microbial activities. Positive matrix factorization analysis confirmed that the PBAPs are mainly derived from local vegetation, pollen, and fungal spores. A higher contribution of PBAP tracers to water-soluble organic carbon (WSOC) was found in summer (14.9%). The annual mean ambient loadings of fungal spores and PBAPs were estimated as 0.49 μg m À3 and 4.12 μg m À3 , respectively, using the tracer method. We report, for the first time, year-round biomarkers of PBAP and soil dust and their contributions to WSOC in the subtropical outflow region of the Asian continent.

Environmental context Water-soluble dicarboxylic acids and related compounds are ubiquitous in atmospheric aerosols. They are abundantly emitted from Asian countries and transported to the Pacific Ocean. During the long-range transport, photochemical processing modifies organic aerosols. We conducted a 1-year observation of diacids and related compounds at Okinawa Island, an outflow region of the Asian Continent, to clarify their sources and photochemical aging. Abstract Ambient aerosol samples were collected for 1 year at Okinawa Island, Japan, and were analysed for water-soluble dicarboxylic acids, oxoacids, α-dicarbonyls and fatty acids to better understand biogenic v. anthropogenic sources and the formation–transformation of organic aerosols during long-range atmospheric transport. Here, we report seasonal variations of diacids and related compounds in Okinawa. We found a predominance of oxalic acid (C2) followed by malonic (C3) and succinic (C4) acid. Total diacids and oxoacids maximised in spring when air masses originated from the Asian Continent with westerly winds. In contrast, phthalic acid (Ph), a tracer of anthropogenic sources, peaked in winter. We found an increased C3/C4 ratio in summer, suggesting an enhanced photochemical aging of organic aerosols. The average ratio of total diacid-C/total carbon (TC) (5.4%) is higher than that (3.1%) from the East China Sea, suggesting that Okinawa aerosols are more aged than East Asian aerosols but less aged compared to those from the remote Pacific including tropics (8.8%). Biogenic short-chain fatty acids and azelaic acid (C9), the latter is a specific oxidation product of unsaturated fatty acids, maximised in summer, whereas higher plant-derived long-chain fatty acids maximised in spring. This study demonstrates that the ambient aerosols in Okinawa are strongly influenced by the Asian outflow in winter and spring and by biogenic organic matter in summer and spring. Enhanced contribution of oxalic acid to aerosol TC in spring suggests that Okinawa organic aerosols are mainly produced in East Asia and photochemically transformed during the transport.

Ambient aerosol samples (TSP, n=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 μg m⁻³ (av. 1.74 ± 1.03 μg m⁻³), 0.07–0.96 μg m⁻³ (0.28 ± 0.19 μg m⁻³), 0.27–1.9 μg m⁻³ (0.73 ± 0.38 μg m⁻³), 0.77 to 3.03 μg m⁻³ (0.58 ± 0.46 μg m⁻³) and 0 to 2.2 μg m⁻³ (0.12 ± 0.23 μg m⁻³), respectively. The average concentration of OC is higher in growing seasons; spring (2.36 μg m⁻³) and summer (1.79 μg m⁻³). Similarly, the highest concentrations of EC and WSOC were found in spring (av. 0.41 μg m⁻³ and 0.95 μg m⁻³, respectively) followed by winter (0.37 and 0.90 μg m⁻³) whereas the lowest concentrations were found in summer (0.19 and 0.52 μg m⁻³, respectively). In contrast, higher concentrations of WSTN were observed in winter (0.86 μg m⁻³) and lower concentrations were observed in summer (0.37 μg m⁻³) and autumn (0.34 μg m⁻³). Similarly, higher concentrations of WSON were observed in early summer (av. 0.26 μg m⁻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 (r = 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⁻ and nss-SO₄²⁻ 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