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Long-Term Trends of Urban Activity Sources Contributing to Organic Carbon (OC) in Different Urban Areas: A Focus on the PM Emission Regulations
ABDULMALIK ALTUWAYJIRI, Milad Pirhadi, Amirhosein Mousavi, Constantinos Sioutas, University of Southern California
Abstract Number: 89
Working Group: Source Apportionment
Abstract
Organic carbon (OC) is extensively attributed to different adverse health outcomes. In this study, we investigated the long-term temporal variations in the sources contributing to OC in central Los Angeles (CELA) and Riverside as source and receptor sites over the 2005-2015 years, a time period during which the tailpipe emissions were stringently regulated. Concentration of different components such as OC, EC, inorganic ions, and ozone were obtained from Chemical Speciation Network database to be input to the positive matrix factorization (PMF) source apportionment model. Five factors including 1) tailpipe emissions, 2) non-tailpipe emissions, 3) biomass burning, 4) secondary organic aerosol (SOA), and 5) local industrial activities were identified for each of the years. Our results showed a decreasing trend in the absolute contribution of tailpipe emissions as well as local industrial activities to the total OC concentrations in the 2005-2015 period at both sites. The contribution of tailpipe emissions to total OC, peaking at cold season, decreased by nearly 60% at both sites, from 3.52 µg/m3 (50%) in 2005 to 1.81 µg/m3 (34%) in 2010 and 1.48 µg/m3 (32%) in 2015 in CELA , and from 3.29 µg/m3 (49%) in 2005, to 1.7 µg/m3 (32%) and 1.24 µg/m3 (34%), respectively, in 2010 and 2015 in Riverside. The SOA contributions to ambient OC showed oscillations over time at both the sampling sites. The biomass contributions were almost constant over the whole period. Furthermore, a general increasing trend in the relative contributions of non-tailpipe emissions to OC were observed in the CELA and Riverside sampling areas. This finding underpins the need for further investigation of and potential regulations on the non-tailpipe emissions in various urban areas, given the developed mitigation strategies for the tailpipe emissions over the recent years.