AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
The Role of Hydrocarbons in the Oxidation of SO2 in Oil Sand Regions
NEDA AMIRI, Ann-Lise Norman, University of Calgary
Abstract Number: 689 Working Group: Effects of NOx and SO2 on BVOC Oxidation and Organic Aerosol Formation
Abstract Secondary sulfate aerosols are formed within the atmosphere through the oxidation of SO2. Homogeneous oxidation of SO2 occurs mostly by hydroxyl radicals and to a minor extent by CH3O2 and HO2. The role of hydrocarbons in the oxidation of SO2 has been investigated extensively, and the importance of stabilized Criegee intermediates (sCI) which are formed from the ozonolysis of alkenes, on SO2 oxidation has been identified. Despite this extensive research, however, the importance of hydrocarbons in SO2 oxidation is not fully understood. The present study investigates the role of hydrocarbons in SO2 oxidation in the oil sand regions of northern Alberta, Canada.
Size-segregated sulfate aerosols were collected on glass fiber filters using a high volume sampler fitted with a cascade impactor from 13 Aug to 5 Sep 2013 on Wood Buffalo Air Monitoring Station 13 (AMS13) site just south of Fort MacKay. Sulfate concentrations were determined for soluble extracts from the filters using Ion Chromatography. Co-located hydrocarbon measurements analyzed using GCMS were made by Daniel Wang and Jeff Brook from Environment Canada.
Daily aerosol sulfate <490nm was compared to total hydrocarbon concentration and to individual hydrocarbons. The correlation for this mainly secondary sulfate fraction and various hydrocarbons were examined. The highest correlations were observed between sulfate and octane (r=0.88, p<0.01) and 1,3-Dimethyl cyclohexane (r=0.87, p<0.01). More than 30 hydrocarbons are well correlated with secondary aerosol sulfate <490 nm diameter having r>0.7 (p<0.0004). The very strong correlation demonstrates the significance of hydrocarbons on secondary sulfate in this size fraction.
Hydrocarbons may be important to consider in the oxidation of SO2 and the formation of secondary sulfate aerosols. Alkanes, cycloalkanes, and aromatic hydrocarbons show the highest correlation with secondary sulfate. A few alkenes also show high correlation but less significant than alkanes and cycloalkanes. This observation is novel and warrants further investigation to identify unidentified oxidation pathways for SO2 and their relative importance.