American Association for Aerosol Research - Abstract Submission

AAAR 36th Annual Conference
October 16 - October 20, 2017
Raleigh Convention Center
Raleigh, North Carolina, USA

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Impact of Secondary Organic Aerosol Tracers on Tracer-based Source Apportionment of Organic Carbon and PM2.5: A Case Study in the Pearl River Delta, China

Qiongqiong Wang, Xiao He, X.H. Hilda Huang, Stephen Griffith, Yongming Feng, Ting Zhang, Qingyan Zhang, Dui Wu, JIAN ZHEN YU, Hong Kong University of Science & Technology

     Abstract Number: 570
     Working Group: Source Apportionment

Abstract
Knowledge of the relative abundance of primary organic aerosol (POA) and secondary organic aerosol (SOA) forms an important scientific basis for formulating particulate matter (PM) control policies. Taking advantage of a comprehensive chemical composition data set of PM2.5 including both POA and SOA tracers, we investigate the impact of inclusion of SOA tracers on the source apportionment of organic carbon (OC) and PM2.5 in the Pearl River Delta (PRD) region of China using positive matrix factorization (PMF). In PMF runs incorporating SOA tracers (PMFw), Ten PMF factors were resolved including four secondary factors: (1) SOA_I (α-pinene, β-caryophyllene and naphthalene derived SOA), (2) SOA_II (isoprene derived SOA), (3) a secondary sulfate factor, and (4) a secondary nitrate factor. In PMF tests without SOA tracers (PMFwo), the SOA_I and SOA_II factors could not be extracted while the remaining eight source factors were resolved. Among the eight common source factors, the industrial emission factor, identified by high loadings of Zn and Pb, showed the largest variations between PMFw and PMFwo solutions. The source contributions of SOA_I and SOA_II resolved in PMFw were largely shifted to the industry emission source in PMFwo. Secondary organic carbon (SOC) summed from the four secondary factors in PMFw contributed ~40% (4.47 μgC/m3) while the SOC estimate by PMFwo (3.51 μgC/m3) was 21% lower due to the inability in extracting SOA_I and SOA_II. Secondary PM2.5 by PMFwo was 6% lower than that by PMFw (23.7 vs 25.2 μg/m3). The PMFw results indicated that SOC from specific precursors may have different formation pathways than secondary sulfate and nitrate formation processes and their source contributions could not be properly resolved without the indicative tracers included in PMF. This study highlights the importance of SOA tracers for estimating SOC contributions using PMF and suggests an urgency to find a more unique tracer for the industrial emission source in the region.