Characterization and Source Apportionment of Nonrefractory Submicron Aerosol Chemistry at the Southern Great Plains Observatory

Submicron atmospheric aerosols play important roles in the climate system, water cycle, and air quality. Characterization of their size distributions and chemical composition can improve the representation of these processes in climate models. While short-term field observations provide important insights into aerosol formation, transport, and processing, long-term observations provide seasonal and yearly trends of aerosol properties. One of the few sites around the world with a multi-year record of aerosol composition measurements is the Southern Great Plains (SGP) atmospheric observatory. SGP is a Department of Energy Atmospheric Radiation Measurement (ARM) user facility field measurement site located in rural north-central Oklahoma, United States. An Aerosol Chemical Speciation Monitor (ACSM) has been in near-continuous operation at SGP since 2011 providing measurements of non-refractory chemical composition of submicron aerosols (organics, ammonium, nitrate, sulfate). In this presentation, long-term SGP ACSM data is combined with co-located measurements of aerosol size distributions, optical properties, and hygroscopicity to characterize seasonal and long-term trends in non-refractory aerosol sources and atmospheric processing. We validate the ACSM performance through comparisons with the 2019 2020 IMPROVE network filter-based chemical measurements obtained at SGP at a sampling rate of one 24 hour sample every third day and with High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) measurements conducted at SGP during the 2016 Holistic Interactions of Shallow Clouds, Aerosols and Land Ecosystems (HI-SCALE) campaign. Because of the length of the SGP ACSM dataset, traditional approaches to source apportionment, such as Positive Matrix Factorization (PMF), are difficult to perform and validate. We use the Multilinear Engine (ME-2) PMF solver and a rolling PMF approach to characterize the nonrefractory submicron chemical composition of the organic aerosol fraction.