Date of Award

2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Oceanography

Specialization

Marine and Atmospheric Chemistry

Department

Oceanography

First Advisor

Brian Heikes

Abstract

Formic acid (HFo) and acetic acid (HAc) have both natural and anthropogenic sources and a role in the atmospheric processing of carbon. These organic acids also have an increasing importance in setting the acidity of precipitation as nitrate and sulfate concentrations have decreased. This dissertation examines HFo and HAc tropospheric formation and transport in the continental United States using observations and models. Observational data from two field campaigns were collected with the peroxide chemical ionization mass spectrometer (PCIMS) using iodide clusters for both HFo and HAc recorded at mass-to-charge ratios of 173 and 187. The first campaign, the Deep Convective Clouds and Chemistry Experiment (DC3), was in May and June 2012 and observations extended from the surface to 13 km over the central and eastern United States. The second campaign, the Front Range Air Pollution and Photochemistry Experiment (FRAPPÉ), was in July and August 2014 with measurements from the surface to 7 km over the Colorado Front Range. Post-mission calibration work determined glycolaldehyde (GA) is a significant isobaric interference to HAc with the HAc:GA sensitivity ranging from 1:1 to 1:10. PCIMS HAc data from both campaigns are reported as the acetic acid equivalent sum (AAES). Based on DC3 model work and estimates of secondary production during FRAPPÉ the instrumental sensitivity was closer to a 1:1. Manuscripts 1 and 2 focus on the DC3 May 21st airmass storm case study at the Alabama/Tennessee border. During this flight a 700 ppt HFo plume at 8 km was observed, approximately 300 ppt in excess of boundary layer air. Different potential reasons for this increase including aqueous production and a pH dependent scavenging were evaluated with the Weather Research and Forecasting model version 3.7 coupled with chemistry (WRF-Chem). Manuscript 1 evaluated the WRF-Chem meteorological reproduction of the airmass storm and the applicability of the Model for Ozone And Related chemical Tracers version 4 and Model for Simulating Aerosol Interactions and Chemistry (MOZART-MOSAIC) compatible microphysics schemes, Morrison and Purdue Lin, in conjunction with a lightning data assimilation (LDA) method. The Morrison microphysics scheme with an LDA temperature range of 261 – 291 K best represented the case study storm. Manuscript 2 showed that there was no difference in WRF-Chem scavenging between a convective complex and isolated convection. It is possible to have cloud top HFo greater than cloud base in a more acidic cloud, pH of 3.5, with multiple HFo aqueous sources, and assuming there is aqueous chemistry up to -40oC. Manuscript 3 investigated HFo and AAES distributions on the Colorado Front Range using three geographic and four chemical classifications. HFo was highest near predominately biogenic sources with the Denver Metropolitan area as the second highest region. AAES was higher than HFo throughout the campaign with the highest AAES in the Denver Metropolitan area and during the Greeley missed approaches. This dissertation highlights that precipitation chemistry influences organic acids in the upper troposphere. Additionally, HFo and HAc gas phase production are controlled by different emission sources which could provide insight into the atmospheric processing of carbon.

Available for download on Friday, April 17, 2020

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