On the Dominant Role of Sulfate Chemistry on New Particle Formation during Summer in Houston

JEREMY WAKEEN, James Smith, Xuanlin Du, Don Collins, O'Donnell Samuel, Jeffrey R. Pierce, University of California, Irvine

     Abstract Number: 445
     Working Group: Aerosol Chemistry

Abstract
New particle formation (NPF) events have been observed in Houston during the summertime, but studies focusing on the gaseous precursors and chemical composition of newly formed particles are lacking. Here we describe results from the TRACER-Ultrafine Aerosol Formation and Impacts (TRACER-UFI) campaign, which took place at the AMF1 main site in La Porte, Texas, from July 1st to August 31st, 2022. The objective of TRACER-UFI is to understand the chemical species and mechanisms responsible for the formation of ultrafine (sub-100-nm diameter) particles in the Houston atmosphere. Our approach combines direct measurements of low‑volatility precursors and size-resolved ultrafine particles together with the UC Riverside Captive Aerosol Growth and Evolution (CAGE) chamber, which is designed to remove ambient particles so NPF from the oxidation of local trace gases can be studied. Our measurements will ultimately be coupled with modeling and co-located measurements of particle hygroscopic properties to infer the impacts of ultrafine particles on clouds and climate.

During TRACER-UFI, we measured the composition of ambient 30-60 nm diameter particles using Thermal Desorption Chemical Ionization Mass Spectrometry (TDCIMS), and gas-phase highly oxidized molecules, including sulfuric acid, with nitrate-CIMS. Ambient measurements were alternated with measurements of gases and particles participating in NPF inside the CAGE chamber. During the daytime, we observed NPF each day inside the CAGE chamber, suggesting that ambient concentrations of gas-phase precursors are sufficient to create NPF and growth if the ambient condensation sink were lower. We measured significant amounts of gas-phase sulfuric acid and particle-phase sulfate in both ambient air and the CAGE chamber throughout the 2-month intensive operational period, alluding to the significance of sulfuric acid in NPF and growth in the urban Houston environment in the summertime.