AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Identify Major Oxalate Salts in PM2.5
Shiguo Jia, Liming Yang, LIYA YU, National University of Singapore
Abstract Number: 241 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Oxalate salts are reported as the major component of total oxalates (oxalic acid and oxalate salts) in PM2.5, and can exhibit a concentration >10 times of oxalic acid. Nevertheless, the dominant species among the oxalate salts remain to be identified. This study develops a thermal evolution method to speciate oxalates in PM2.5 as thermal sensitive vs. thermal resistant oxalates. The method coupled with a previously established analytical method is tested with individual oxalate standard compounds, verified with standard mixture oxalate salts, and applied to PM2.5 samples collected in a warm humid tropical atmosphere.
The sampling period was accompanied with ample daily rainfall (up to 23 mm) and an averaged PM2.5 concentration of 17.1±4.8 µg/m3 (n = 8). Results show that ammonium oxalates, which are thermal sensitive, are the most dominant oxalate salt in PM2.5 with a concentration ranging from 148–255 ng/m3. This is 9–18 times of the concentration of oxalic acid, and corresponds to 84–89% of total oxalates. Non-ammonium oxalates which are thermal resistant are responsible for 3–7% of total oxalates in the collected PM2.5 samples, contributing little to the tropical urban atmosphere. The amount of ammonium associating with oxalates ranged from 30–104 ng/m3, corresponding to 3–10% of the total ammonium in PM2.5 collected from the relatively clean atmosphere. This suggests that the amount of ammonium in PM2.5 which is available to neutralize acidic components can be lower than the quantifiable amount.