Seminar

Abstract

Particulate matter (PM2.5) pollution is a significant air quality issue in many areas of the world. In several areas in the western US, wintertime PM2.5 exceedances are frequent and often have large contributions from ammonium nitrate aerosol, formed from gas phase reactions of NOx, VOCs, and NH3. Using observations from the recent Utah Winter Fine Particulate Study in the Salt Lake Valley, we modeled the growth of ammonium nitrate aerosol using the parameter Ox,total, which describes both O3 production and HNO3 production, and demonstrates that the two are closely linked. These results indicate that the same NOx-VOC framework that has often been used to assess O3 control strategies is also appropriate for ammonium nitrate control under some circumstances. We find that ammonium nitrate aerosol formation in the SLV is VOC-limited and would therefore be best controlled by initially reducing VOC emissions rather than NOx emissions. This may also have implications for control strategies in urban areas in East Asia, where NOx emissions have recently begun to decrease, but VOC emissions continue to rise.

In the second part of this talk, I will discuss recent results from controlled burns at the Missoula Fire Sciences Lab. Summertime wildfires release large quantities of gas- and particulate-phase emissions, affecting air quality and human health in the western US and elsewhere. Using an updated broadband cavity enhanced spectrometer and an aerosol size-selection inlet, we have made measurements of the complex refractive index of aerosol particles generated by biomass burning. I will discuss updates to that instrument and the challenges involved in characterizing the optical properties of aerosol which are both non-spherical and light-absorbing.

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Carrie Womack earned a PhD in Physical Chemistry from the University of Chicago, where her research focused on laboratory studies of radical intermediates. She then spent two years at MIT as a Camille and Henry Dreyfus Foundation Postdoctoral Fellow, measuring Criegee intermediates. In August 2015, she joined the NOAA Chemical Sciences Division as a National Research Council Fellow.