Issue 5, 2024

Chemically specific sampling bias: the ratio of PM2.5 to surface AOD on average and peak days in the U.S.

Abstract

Accurate quantitative description of the atmospheric fine particulate matter (PM2.5) burden requires an understanding of aerosol amounts and properties that transcends measurement platforms. For example, air quality studies often seek to describe ambient PM2.5 with columnar aerosol optical depth (AOD), point measurements of mass, or some combination. PM2.5 chemical constituents affect such measurements differently. We investigate the ratio of PM2.5-to-AOD (η) from 2005 to 2016 at multiple surface locations across the contiguous U.S. using observations and models, and quantitatively account for PM2.5 sampling bias of nitrate and aerosol liquid water (ALW). We find η peaks during winter and is lowest in summer at all locations, despite contrasting seasonality in PM2.5 mass and AOD. Accounting for loss of nitrate and ALW from PM2.5 monitors improves consistency among η calculations in space and time. Co-occurrence of extreme PM2.5 mass concentrations and AOD events declined in the eastern U.S. but not in the west. On peak days, in all locations, ALW mass concentrations are higher and fractional contributions are larger relative to PM2.5 chemical composition during average conditions. This suggests an increased fraction of ambient PM2.5 is detectable via optical methods but not well described by surface mass networks on peak days. The Community Multiscale Air Quality (CMAQ) model reproduces similar spatial and temporal variability in η to surface observations in winter and summer simulations at the beginning and end of the analysis period. Accounting for sampling artifacts in surface monitors may improve agreement with model predictions and remote sensing of PM2.5 mass concentrations. The poor understanding of organic compounds and their PM2.5 sampling artifacts remains a critical open question.

Graphical abstract: Chemically specific sampling bias: the ratio of PM2.5 to surface AOD on average and peak days in the U.S.

Supplementary files

Article information

Article type
Paper
Submitted
17 Nov 2023
Accepted
03 Apr 2024
First published
03 Apr 2024
This article is Open Access
Creative Commons BY license

Environ. Sci.: Atmos., 2024,4, 547-556

Chemically specific sampling bias: the ratio of PM2.5 to surface AOD on average and peak days in the U.S.

S. Rosanka, M. M. Flesch, Y. T. T. Chiu and A. G. Carlton, Environ. Sci.: Atmos., 2024, 4, 547 DOI: 10.1039/D3EA00163F

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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