Submitted as: development and technical paper
30 Nov 2022
Submitted as: development and technical paper | 30 Nov 2022
Status: this preprint is currently under review for the journal GMD.

Source Attribution of Ozone and Precursors in the Northeast U.S. Using Multiple Photochemical Model Based Approaches (CMAQ v5.3.2 and CAMx v7.10)

Qian Shu, Sergey L. Napelenok, William T. Hutzell, Kirk R. Baker, Benjamin Murphy, Christian Hogrefe, and Barron H. Henderson Qian Shu et al.
  • U.S. Environmental Protection Agency, Research Triangle Park, NC, 27711, USA

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 attribution fully from nitrogen oxide reactants, fully from volatile organic compound (VOC) reactants, equally to all reactants, or dynamically to NOx or VOC reactants based on the indicator gross production ratio of hydrogen peroxide (H2O2) to nitric acid (HNO3). This study's primary objective is to document these ISAM updates and demonstrate their impacts on source apportionment results for O3 and its precursors. Additionally, the ISAM results are compared with the Ozone Source Apportionment Technology (OSAT) in the Comprehensive Air-quality Model with Extensions (CAMx) and the brute force method (BF). All comparisons are performed for a 4 km horizontal grid resolution application over the northeast U.S. for a selected two-day summer case study (August 9th and 10th, 2018). General similarities among ISAM, OSAT, and BF results add credibility to the new ISAM algorithms. However, some discrepancies in magnitude or relative proportions among tracked sources illustrate the distinct features of each approach while others may be related to differences in model formulation of chemical and physical processes. Despite these differences, OSAT and ISAM still provide useful apportionment data by identifying the geographical and temporal contributions of O3 and its precursors. Both OSAT and ISAM attribute the majority of O3 and NOx contributions to boundary, mobile, and biogenic sources, whereas the top three contributors to VOCs are found to be biogenic, boundary, and area sources.

Qian Shu et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2022-273', Anonymous Referee #1, 28 Dec 2022
  • RC2: 'Comment on gmd-2022-273', Anonymous Referee #2, 03 Jan 2023
  • CEC1: 'Comment on gmd-2022-273', Astrid Kerkweg, 06 Jan 2023

Qian Shu et al.


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Short summary
Source attribution methods are generally used to determine culpability of precursor emissions sources to ambient pollutant concentrations. However, source attribution of secondarily formed pollutants such as ozone and its precursors cannot be explicitly measured, making evaluation of source apportionment methods challenging. In this study, multiple apportionment approach comparisons show common features but still reveal wide variations in predicted sector contribution and species dependency.