Chemical Identification of New Particle Formation and Growth Precursors through Positive Matrix Factorization of Ambient Ion Measurements
DANIEL KATZ, Aroob Abdelhamid, Harald Stark, Manjula Canagaratna, Douglas Worsnop, Eleanor Browne,
University of Colorado Boulder & CIRES Abstract Number: 522
Working Group: Aerosol Chemistry
AbstractAmbient gas-phase molecular ions and ion–molecule clusters determine atmospheric electrical properties and promote new particle formation (NPF). In the lower troposphere, positive and negative charges are respectively transferred to the most basic and most acidic species. Measurements of ambient ions and clusters are therefore highly selective towards poorly characterized species thought to be important for NPF and growth. Because NPF affects the atmospheric radiation budget and hydrologic cycle, understanding the global impacts of NPF requires better insight into the chemical precursors of NPF in diverse regions. Agricultural regions represent a major land use category, but a lack of trace gas measurements in such regions impedes understanding of how crop emissions contribute to secondary aerosol. We measured ambient ion composition using an atmospheric pressure interface time-of-flight mass spectrometer (APi-ToF) during one month of the 2016 Holistic Interactions of Shallow Clouds, Aerosols, and Land Ecosystems campaign in the agricultural Southern Great Plains region. We use binned positive matrix factorization (binPMF) and generalized Kendrick analysis (GKA) to constrain chemical formulas of observed ions and reveal their temporal variation without the need for long-timescale averaging or a priori high-resolution peak fitting. Clusters charged by NO
3- and HSO
4- core anions dominate negative ion mode observations. Both anions cluster with sulfuric acid, nitric acid, and organic compounds including organosulfates. Highly oxygenated organic molecules (HOMs) derived from monoterpene (MT) and sesquiterpene (SQT) oxidation
are observed as NO
3- clusters. Organonitrates derived from NO
3 radical oxidation of SQTs account for most of the HOM signal and, along with other SQT oxidation products, likely contribute to particle growth at the site. We suggest that SQTs represent an underappreciated source of secondary organic aerosol in agricultural regions. We show that binPMF analysis of APi-ToF measurements provides insight into the temporal evolution of compounds important for NPF and growth.