Multi-year, high-time resolution aerosol chemical composition and mass measurements from Fairbanks, Alaska†

Abstract

Fairbanks-North Star Borough, Alaska (FNSB) regularly experiences some of the worst wintertime air quality in the United States. Exceedances of the EPA's 24 h fine particulate matter (PM_2.5) rule are common, and can last for weeks-long periods. Here we present sub-hourly measurements of chemically-speciated aerosol measurements over a 25 month span from an Aerosol Chemical Speciation Monitor (ACSM). This dataset includes measurements from all four seasons and over three separate winters (2020, 2021, 2022). It spans a long enough duration to provide an overview of typical seasonal and diurnal variations in aerosol concentrations, composition, and sources in Fairbanks. We observe consistent high PM_2.5 concentrations in wintertime, which is dominated by organic aerosol (OA) and, to a lesser extent, sulfate (SO₄). We perform factor analysis of the OA using Positive Matrix Factorization (PMF), which reveals three factors, two of which are attributable to primary sources. These primary OA factors are highest in concentration and fractional contribution during wintertime. We show that high concentration periods are correlated with cold temperatures, and enriched in those organic aerosol components related to primary emissions. High concentration periods are also enriched in SO₄, though we show that some of the “SO₄” measured by the ACSM is very likely organosulfur compounds, which are more prevalent at high concentrations. We also show that within winter, there are significantly different diurnal patterns in PM components depending on meteorological parameters. This analysis is important for understanding air quality patterns in Fairbanks, and as context for the 2022 ALPACA measurement campaign.