Source apportionment of PM2.5 at two Seattle chemical speciation sites

Abstract

ABSTRACT Positive Matrix Factorization analysis of PM2.5 chemical speciation data collected from 2015–2017 at Washington State Department of Ecology’s urban NCore (Beacon Hill) and near-road (10th and Weller) sites found similar PM2.5 sources at both sites. Identified factors were associated with gasoline exhaust, diesel exhaust, aged and fresh sea salt, crustal, nitrate-rich, sulfur-rich, unidentified urban, zinc-rich, residual fuel oil, and wood smoke. Factors associated with vehicle emissions were the highest contributing sources at both sites. Gasoline exhaust emissions comprised 26% and 21% of identified sources at Beacon Hill and 10th and Weller, respectively. Diesel exhaust emissions comprised 29% of identified sources at 10th and Weller but only 3% of identified sources at Beacon Hill. Correlation of the diesel exhaust factor with measured concentrations of black carbon and nitrogen oxides at 10th and Weller suggests a method to predict PM2.5 from diesel exhaust without a full chemical speciation analysis. While most PM2.5 sources exhibit minimal change over time, primary PM2.5 from gasoline emissions is increasing on average 0.18 µg m−3 per year in Seattle. Implications This study utilizes Positive Matrix Factorization to determine PM2.5 sources from chemical speciation measurements at two urban Seattle sites from 2015-2017. The paper reports PM2.5 source trends, and extends previous source apportionment analyses in Seattle to the present day. The study also quantifies diesel PM2.5 at a near-road site, and describes a predictive model that allows estimation of the contribution of diesel PM2.5 to the total measured PM2.5 at near-road sites across the country without a full chemical speciation analysis.