. From where Aerosols Are Born to where Aerosols Die:Study of the Global Chemical Production and Properties of Secondary Aerosol

Abstract
Secondary aerosols impact air quality, human health, gas-phase chemistry, and climate. However, models have difficulty in capturing and predicting the amount (production) and speciation (properties) of secondary aerosol. Here, I will be presenting results from two studies I am completing. First, concerning secondary organic aerosol (SOA) produced in urban area, I have been analyzing observations collected from megacities on three continents. I have found that the production of urban SOA has a robust relationship with emissions of key aromatic compounds. I use this relationship to apportion the sources of urban SOA from transportation versus volatile chemical products. I find that the volatile chemical products lead to the different urban SOA concentrations observed in the different cities. These results are used to constrain SOA production in a chemical transport model to predict the number of premature deaths that could be avoided by regulated urban SOA precursors. Second, in regards to secondary inorganic aerosol (SIA), I have been analyzing observations collected from eleven different airborne campaigns to determine how the aerosol acidity and ammonium balance changes from source regions to the most remote regions (measurements from the center of Pacific and Atlantic Oceans and the poles during the ATom-1 and -2 campaigns). I find a robust relationship with both ammonium balance and aerosol acidity versus total SIA mass concentration. Most chemical transport models cannot replicate these results, indicating that the models (1) are unable to predict the chemical and physical properties of SIA observed in the field and (2) either have too much NH3, too long total NHx (NH3 + NH4+) lifetime, or too low sulfate (either concentration or production). I am currently investigating what could be leading to these large differences, as it impacts gas-phase uptake to aerosol and how well the aerosol behaves as cloud condensation nuclei.