| Summary: | 碩士 === 國立中央大學 === 環境工程研究所 === 101 === This work collected armospheric aerosols at Son La, Vietnam and Mt. Lulin Atmospheric Background Site (LABS), Taiwan, respectively. The objectives of this study were to survey Son La and LABS aerosol characteristics, distinguish aerosol chemistry between biomass burning (BB) and non-biomass burning (NBB) periods from 2003-2012, realize the changes of aerosol composition proportion for BB plume transported from Indochina and LABS, and utilize Positive Matrix Factorization (PMF) (US EPA, 2008) for resolving aerosol source contribution at LABS.
The results show that PM2.5 dominates PM10 at Son La in 2012. The airmasses were traced back from Indochina and South China by using Hysplit model (Draxler and Rolph, 2010). PM2.5 mass concentration, K+, carbonaceous content, and organic aerosol proportion were greater than that from South China when the airmasses were from Indochina. This implies that aerosol composition is influenced much by BB activities. In contrast, SO42- and NH4+ were higher in PM2.5 mass fractions to indicate the greater influence from anthropogenic sources.
The results from ten years’s observation at LABS show that PM2.5 mass concentration, K+, NO3-, Levoglucosan, OC3, and EC1-OP were obviously greater than that of NBB. This phenomenum not only demonstrates the increase of M2.5 mass concentration but also stands out aerosol tracer characterstics from BB plume. On the other hand, the proportion of aerosol water-soluble ions from BB plume was lower than NBB plume, which indicates NBB aerosol is influenced more by anthrpogenic sources.
In the past, near-source BB aerosol characteristics were less studied. This work compares PM2.5 observation data from Chiang Mai, Thailand in 2010, Son La in 2011-2012, and LABS in 2010-2012 to show that the variations of BB aerosol tracers such as PM2.5 K+, OC3, EC1-OP, and Levoglucosan were more stable than the other species for near-source BB aerosol and downstream LABS aerosol affected by BB plume. In addition, the proportion of NO3- in LABS PM2.5 during BB period was higher than that of Chiang Mai and Son La, which implies NO3- is transformed from long-range transport.
The source contributions of LABS PM2.5 resolved from PMF shows that six major pollution types from high to low are BB mixing secondary aerosol (28.7 %), BB mixing soil dust (25.4 %), BB (17.6 %), BB _ dicarboxylates (12.0 %), Diesel emissions (10.0 %), and Sea salt (6.2 %). PMF source apportionment indicates 83.7% of PM2.5 mass concentration is contributed from BB for the airmasses under the influence of BB plume. This confirms the correctness of PMF source apportionment and accounts for BB plume mixing with other airmasses during transport to reach downstream LABS under the prevailing west wind. In contrast, secondary aerosol contributed more than other sources to PM2.5 to account for 70.6% during NBB period. In addition, the airmasses were mostly originated from ocean (including Pacific Ocean and South China Sea) but some mixed with marine and anthropogenic primary pollutants were transported from costline of China mainland through lower atmosphere to LABS.
In summary, PM2.5 is abundant for near-BB source Son La aerosol. Moreover, PM2.5 is influenced more by BB activities when the air masses were from Indochina and anthropogenic sources affect PM2.5 more for air masses from South China. Ten years’s LABS aerosol observation data indicate that BB plume could mix with less other sources during long-range transport and NBB airmasses mainly contain secondary aerosol but might have mixed with marine and anthropogenic primary pollutants.
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