Long-Term Measurements of Submicrometer Aerosol Chemistry at the ARM Southern Great Plains Site

Summary

Aerosols are a large source of uncertainty in climate model predictions of radiative forcing.  To evaluate aerosol processes in global models, colocated measurements of meteorology, radiation, and aerosols are needed. A team of scientists funded by the Department of Energy’s Atmospheric System Research (ASR) program and the Atmospheric Radiation Measurement (ARM) Climate Research Facility studied long-term trends of submicrometer aerosol composition and mass concentration measured by an aerosol chemical speciation monitor (ACSM) at the ARM Southern Great Plains (SGP) site. They measured organic mass spectral matrix using a rolling window technique to derive distinct source factors, evolution processes, and physiochemical properties. The rolling window approach enabled the capture of dynamic variations of the chemical properties in the organic aerosol factors over time.

The team found that organics dominated the observed aerosol mass concentration for most of the study with the exception of winter, when ammonium nitrate increases due to cooler temperatures and the transport of gaseous precursors from surrounding urban and agricultural areas. Sulfate mass concentrations have little seasonal variation and have mixed regional and local sources. In the spring, biomass burning organic aerosol emissions increase and are mainly associated with local fires. Isoprene and carbon monoxide emission rates represent the spatial distribution of biogenic and anthropogenic sources, respectively. The combined spatial distribution of isoprene emissions and air mass trajectories suggest that biogenic emissions from the southeast contribute to secondary organic aerosol formation at the SGP site during the summer.

The observations illustrate that aerosol particles at the SGP site derive from a complex mixture of local sources, with varying seasonal behavior, and atmospheric transport. In combination with colocated measurements of meteorology and radiation, the long-term aerosol chemistry measurements at the SGP site can be used to evaluate the treatment of these complex processes in regional and global climate models.

References

Parworth, C., J. Fast, F. Mei, T. Shippert, C. Sivaraman, A. Tilp, T. Watson, and Q. Zhang. 2015. “Long-Term Measurements of Submicrometer Aerosol Chemistry at the Southern Great Plains (SGP) Using an Aerosol Chemical Speciation Monitor (ACSM),” Atmospheric Environment 106, 43-55. DOI: 10.1016/j.atmosenv.2015.01.060.