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Comparing Online and Offline Measurements of Ice-Nucleating Particles from Two Autumn Field Campaigns
ELISE WILBOURN, Larissa Lacher, Hemanth Sandeep Kumar Vepuri, Jens Nadolny, Ottmar Möhler, Naruki Hiranuma, West Texas A&M University
Abstract Number: 272
Working Group: Aerosols, Clouds and Climate
Abstract
Atmospheric ice-nucleating particle (INP) concentrations are a source of uncertainties in current climate models, partially due to a lack of global-scale INP measurements. INPs were traditionally measured using either offline or in-situ measurements, both involving large quantities of time and labor. Advancements using the Portable Ice Nucleating Experiment (PINE) chamber, a remotely operated expansion chamber working continuously, allow for longer INP measurement periods at time scales of 8-15 minutes per measurement. Recently, PINE was deployed on two field campaigns, first from October 1 – November 15, 2019 in Oklahoma, USA (referred to as southern great plains, SGP), and second from October 1, 2020 – March 28, 2021 on Graciosa Island, Azores, Portugal (referred to as eastern north Atlantic, ENA). These sites have drastically different aerosol concentrations and sources. PINE measured INP concentrations relevant for mixed-phase cloud formation, but the chamber is limited by statistical accuracy to temperatures below -15 °C with current methods, limiting information on higher-temperature INPs during these campaigns. To address this limitation, aerosol particles were also collected on filters at a several-day time scale for offline analysis using a droplet freezing assay to assess associated INP concentrations. Here we compare measurements taken with PINE and those measured with offline techniques. Although SGP and ENA measurements were taken during the same season, the filter measurements and PINE measurements indicate that the terrestrial SGP site has a consistently higher INP concentration, potentially driven in part by higher overall particle concentration. This is in line with previous studies indicating INP concentrations at terrestrial sites tend to be one to two orders of magnitude higher than concentrations at marine sites like ENA. Our preliminary results suggest good agreement between online and offline techniques, validating the use of a multi-instrument technique to measure INP concentrations.