Comparison of ozone formation attribution techniques in the northeastern United States

Abstract. The Integrated Source Apportionment Method (ISAM) has been revised in the Community Multiscale Air Quality (CMAQ) model. This work updates ISAM to maximize its flexibility, particularly for ozone (O3) modeling, by providing multiple attribution options, including products inheriting fully from nitrogen oxide reactants, volatile organic compound (VOC) equally all or dynamically NOx VOC reactants based on indicator gross production ratio of hydrogen peroxide (H2O2) nitric acid (HNO3). updated incorporated into most recent publicly accessible versions CMAQ (v5.3.2 and beyond). study's primary objective is document these demonstrate their impacts source apportionment results O3 precursors. Additionally, are compared with Ozone Technology (OSAT) Comprehensive Air-quality Model Extensions (CAMx) brute-force method (BF). All comparisons performed a 4 km horizontal grid resolution application over northeastern US selected 2 d summer case study (9 10 August 2018). General similarities among ISAM, OSAT, BF add credibility new algorithms. However, some discrepancies magnitude relative proportions tracked sources illustrate distinct features each approach, while others may be related differences model formulation chemical physical processes. Despite differences, OSAT still provide useful data identifying geographical temporal contributions Both attribute majority boundary, mobile, biogenic sources, whereas top three contributors VOCs found biogenic, area sources.