10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Short-interval Aerosol Water-soluble Inorganic Ions Observed under the Influence of Upslope Wind, Transported Biosmoke, and Fog at Mountain Lulin, Taiwan
CHUNG-TE LEE, Wei-Ren Chen, Shih-Yu Chang, Charles C.K. Chou, Neng-Huei Lin, National Central University, Taiwan
Abstract Number: 491 Working Group: Aerosol Chemistry
Abstract Field campaigns were conducted at Lulin Atmospheric Background Station (LABS) from October to November 2015 and March to April 2016. Short-interval variations of water-soluble inorganic ions (WSIIs) of PM2.5 (an aerodynamic diameter equal to or less than 2.5 μm) were monitored using particle-into-liquid sampler coupling with ion chromatographers (PILS-IC). Meanwhile, PM2.5 mass concentration, PM10 and PM1 aerosol absorption and scattering coefficients, aerosol total number concentration, aerosol number and volume size distributions, and gaseous pollutants were also measured at LABS.
The comparisons of WSIIs (SO42-, NO3-, NH4+, and K+) between integrated PILS-IC data and collocated filter samples indicated that the measurements were consistent (R2 ≥ 0.75) with each other. In autumn sampling, upslope wind resulted in an increase of PM2.5 from 6.9 ± 2.1 to 11.5 ± 2.3 µg m-3 in average. During the spring campaign, five-day backward trajectories were mostly originated from far west of Indochina in March but changed to from the Philippines in April. The average PM2.5 mass concentration of spring (17.5 ± 7.89 μg m-3) was more than twice that of autumn (8.0 ± 2.9 μg m-3) after excluding rainy periods. Transported biomass burning (BB) smoke form Indochina was verified to cause high PM2.5 mass concentration in spring, which, however, masked upslope wind effects. Ion equivalent evaluation indicated that the molar ratio of [NO3-]/[SO42- ] increased linearly as the molar ratio of [NH4+]/[SO42-] exceeded beyond 1.5. During the BB period, the molar ratio of [NH4+]/(2[SO42-]+[NO3-]) at 0.88 ± 0.25 showed a near complete neutralization among major ions in spring. In the third to fifth selected BB events, average PM2.5 mass concentration was 24.9 ± 12.7 μg m-3, while average NH4+, SO42-, NO3-, and K+ concentration were 1.7 ± 1.0, 3.7 ± 1.4, 1.4 ± 1.0, and 0.3 ± 0.2 μg m-3, respectively. Excess NH4+ (after neutralizing with SO42-) correlated well with NO3- (R2 ≥ 0.70) indicating NO3- was formed through homogenous gas phase reactions. Four fog events occurred in the three selected BB events, aerosols were observed either diluted by clean air or grown in fog. In addition, aerosol number size distributions presented a unimodal distribution during BB events, while bimodal distributions were observed in the fog events.