Biogenic Effects on New Particle Formation at an Alpine Site in Colorado

ANNA KAPP, Darielle Dexheimer, Gregory W. Vandergrift, Zhenli Lai, Nurun Nahar Lata, Swarup China, Zezhen Cheng, James Smith, Univeristy of California, Irvine

     Abstract Number: 444
     Working Group: Remote and Regional Atmospheric Aerosol

Abstract
The Surface Atmosphere Integrated Field Laboratory (SAIL) was a unique long-term field campaign that took place in southwestern Colorado, USA, 1 September 2021 - 15 June 2023. One of the objectives of SAIL was to explore the seasonal variability of particle sources and sinks, which has implications on the life cycle of aerosols and their impacts on atmospheric and surface radiative budgets. The SAIL site saw frequent new particle formation (NPF) events during the observation period. This presentation explores the seasonal variability of NPF events and compares aerosol composition during a period of intense NPF to a period without events. Size distributions obtained with a scanning mobility particle sizer showed an increase in atmospheric NPF events during the winter-spring transition period (February-June) and, to a lesser extent, the fall-winter transition period (September-December). Summertime (June-July-August) was characterized by dominant ~100 nm mode and no clear nucleation mode.

Twelve-hour samples of bulk aerosols were collected on Polytetrafluoroethylene (PTFE) filters during and after an NPF event in May 2023. Data from these filter samples indicates that the relative abundance of sesquiterpene oxidation products in aerosol was elevated when NPF was taking place and decreased afterwards. In concert with the sesquiterpene oxidation products, the molecular weight of the average compound was at a maximum of 230 amu during the NPF event, this decreased to 217 amu after the NPF event. Conversely, the average O:C ratio was at a minimum of 0.5 during the NPF event, this ratio went up to 0.67 after the event. NPF therefore appears to be driven by an increase in larger but less oxidized compounds. Overall, the molecular level data showed that NPF events may be associated with biogenic volatile organic compounds, which points to the ways local ecology can affect particle formation and growth.