| dc.description.abstract | Mt. Lulin (2,862m a.s.l.) is a suitable site to assess pollution transport from East Asian continent and West Pacific background. This study observed atmospheric aerosol at Mt. Lulin from September 2008 to April 2009 and split the collected samples into from biomass-burning (BB) and non-biomass-burning (NBB) periods. Aerosol water-soluble ions are dominated by sulfate and ammonium ions during both BB and NBB periods. However, aerosol nitrate and potassium ion levels were noticeably increased during BB period. For aerosol carbons during BB period, OC3 and EC1-OP were the major fractions in organic carbon (OC) and elemental carbon (EC), respectively. In contrast, OC1 in OC and EC2 in EC were the two dominant carbon fractions during NBB period. Aerosol levoglucosan was the only dominant species in aerosol anhydrous monosaccharide during both BB and NBB periods. The level of aerosol levoglucosan was significantly increased during BB period. Oxalic acid was the dominant dicarboxylic acids during both BB and NBB periods. This implies that oxalic acid is the precursor species or the end product of other dicarboxylic acids. The concentration of aerosol oxalic acid was also increased during BB period.
Aerosol water-soluble organic carbon (WSOCp) was specifically observed during observation period. The analysis reveals that low-temperature volatiled OC2 and OC3 are the major fractions of WSOCp. The concentration of WSOCp had a better correlation with BB tracers during BB period. It indicates that the WSOCp can be a good tracer for BB event. Atmospheric temperature is found having a good correlation with WSOCp. Rain fall may significantly reduce WSOCp concentration but not for gaseous water-soluble organic carbon (WSOCg). By excluding raining events, the fraction of WSOCp in (WSOCp+WSOCg) is increased when the relative humidity is above 70%. In Mt. Lulin aerosol, sulfate ion is mainly combined with ammonium ion (R2=0.90) and less with calcium and sodium ions. The compound form of sulfate and ammonium ions is (NH4)3(H)(SO4)2.
During the study period, ammonia gas was found insufficient in neutralizing sulfuric and nitric gases. Although more aerosol nitrate was observed during BB period, nitric gas is not a major acidic gas in neutralizing ammonia gas. The mole ratio of measured over calculated aerosol ammonium ions (?NH4+?meas/?NH4+?calc) is averaged at 0.79 for the period of 2007－2009. This value is not deviated too much from 0.8 at Jungfracjoch in European Swiss Alps observed during 1999－2005. It indicates that the ammonia gas in middle Europe and East Asia is insufficient in neutralizing sulfuric and nitric gases. By considering longer BB period and higher linear correlation for ?NH4+?meas/?NH4+?calc with aerosol sulfate and nitrate (R2=0.53 and 0.32, respectively) in 2009 spring, this study infers that ammonia gas probably needs more time in neutralizing sulfuric and nitric gases to form sufficient aerosol sulfate and nitrate.
Five cloud events were observed to collect aerosols at pre-cloud, in-cloud, and post-cloud periods in this study, respectively. Four cloud events transported aerosols to the collection site. Excess ammonium ion not neutralized is found in cloud event. The activation efficiency of water-soluble ions in the cloud event is the best for nitrate ion, followed by sulfate and ammonium ions. For aerosol carbon fractions, the scavenging ratio of OC is similar in different time periods. PM1 concentration is observed to drop after cloud event, which is probably due to cleaner air masses transported to the site.
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