Atmospheric processing of chemical compounds and direct measurements of particle loss by dry and wet deposition
Date
2019
Authors
Emerson, Ethan Walker, author
Farmer, Delphine, advisor
Neilson, James, advisor
Ravishankara, A. R. Ravi, committee member
Borch, Thomas, committee member
Barisas, George, committee member
Jathar, Shantanu, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Anthropogenic pollutants, like NOₓ and black carbon (BC), are ubiquitous in the atmosphere and impact human health and the climate. Understanding the atmospheric fate of such pollutants is critical in understanding their impact. This work focuses on understanding the loss of two key pollutants: the chemical termination of gas phase NO and NO₂ (NOₓ) and the deposition of refractory black carbon (rBC) particles. Additionally, because the tools to analyze particle fluxes and coated rBC are lacking, this work describes the development of software to analyze particle fluxes and estimate the thickness of organic coatings on rBC. Removal of aerosols from the atmosphere occurs via wet and dry deposition. Black carbon (BC) is one form of aerosol that impacts atmospheric temperature, cloud formation and properties, the albedo of snow and ice surfaces, and the timing of snowmelt. Parameterization of BC dry deposition is particularly limited due to the lack of available instrumentation for measuring the process, and thus there is a lack of observational datasets with which to evaluate existing models. We present observations of dry and wet deposition rates of size-resolved coated rBC and total aerosol number by eddy covariance technique using a single particle soot photometer (SP2; Droplet Measurement Technologies Inc.) and ultra high sensitivity aerosol spectrometer (UHSAS; Droplet Measurement Technologies Inc.) from the remote Southern Great Plains ARM Climate Research facility in north-central Oklahoma. Using these data, we show that (1) wet deposition dominates the removal of rBC from the atmosphere, (2) dry deposition measurements agree with sophisticated deposition parameterizations, and (3) a simple parameterization adequately describes size-resolved deposition. We assess the implications of this parameterization in GEOS-Chem. Size-resolved deposition schemes, such as those used in current chemical transport models use schemes that have not been compared to recent measurements. Using aggregated deposition velocities from literature observations and those collected by our group, we show that the current scheme used in chemical transport models does not accurately describe observed deposition velocities. Highly sophisticated leaf level models can accurately describe the aggregated observations, but they are ill-suited to global chemical transport models. We present a simple scheme that reasonably describes size-resolved particle deposition in a simple sectional scheme that includes atmospheric parameters. The result of this update is substantial changes in particle concentrations across the globe and these impact cloud condensation nuclei, the direct and indirect effects, and PM2.5 concentrations. NOₓ is a key pollutant that propagates atmospheric chemistry through the coupled HOₓ-NOₓ cycle. Trace gas measurements from the 2015 spring and summer SONGNEX campaign conducted at the Boulder Atmospheric Observatory (BAO) in Northern Front Range Metropolitan Area of Colorado (NFRMA) are characteristic of environment impacted by oil and natural gas, agricultural operations, traffic, biogenic, and urban sources. Using a previously published PMF analysis of volatile organic compounds, we show the impact of a changing atmospheric composition due to emissions from anthropogenic sources on NOx sinks and the implications of HOₓ-NOₓ propagation through box modelling. These results indicate that the NFRMA is sensitive to NOₓ and VOC mixing ratios during spring, summer, and smoke-impacted periods.