An alternative analysis of new particle formation : studying the misfits to understand the norm

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Title: An alternative analysis of new particle formation : studying the misfits to understand the norm
Author: Buenrostro Mazon, Stephany
Contributor: University of Helsinki, Faculty of Science
Doctoral Programme in Atmospheric Sciences
Institute of Atmosphere and Earth System Research
Publisher: Helsingin yliopisto
Date: 2019-10-25
Language: en
Thesis level: Doctoral dissertation (article-based)
Abstract: In Finland, with each breath you are inhaling a luxury product: clean air. This is not the case for most people, as 90% of the human population lives within polluted air according to the World Health Organization. In addition to gas molecules, there are tiny solid or liquid particles floating in our air. We refer to this particle and gas mixture as an aerosol. Some aerosol particles are injected directly into the atmosphere from emissions like biomass burning or industries. The other half or more (~50-70%) are created in the air from precursor vapors in what is termed new particle formation (NPF) events. However aerosols are not only infamously involved in air quality, but play a major role in climate: they scatter incoming solar radiation, and indirectly affect climate by serving as the seeds that form clouds. In both cases, aerosols have an overall cooling effect, offsetting the global warming from greenhouse gases. Yet aerosols and aerosol-cloud interactions have the largest uncertainty in our climate budget estimates. It is thus with urgency that we must concretize the sources, concentrations, and life-cycles of atmospheric particles around the world. However, while NPF events have been observed almost everywhere worldwide, global comparisons and quantification of NPF dynamics are mostly based on ideal, regional processes. As a result, a large fraction of field data is discarded from further analysis. In this thesis, we compared ideal NPF events to discarded, ambiguous or small-scale events in order to understand their potential contribution to aerosol dynamics and number concentrations. We first determined the optimal ambient conditions for regional NPF in a boreal forest at SMEAR II station in Finland: clear-sky, sunny days, with low background aerosol concentrations, moderate temperatures, low relative humidity and high concentrations of oxidized organic vapors. We then reclassified the undefined days from 11 years of data (~40% of total data) to include transported/advected events and bursts of nucleation mode ions and particles that failed to grow to larger sizes. We consequently developed an automated classification scheme that accounts for both regional NPF events and the new classes of previously undefiend days. The result is a more robust analysis of NPF processes. We observed frequent nocturnal clustering in Hyytiälä (~30% of 11 years of data). Specifically, 1.5 to 2 nm ion concentrations were ~2 times higher at night than during daytime NPF events. However, this phenomenon disappears after ~3 nm cluster sizes. We conclude that a boreal nighttime forest is an effective source of sub-3 nm clusters that fail to grow. Lastly, we compared nucleation mode aerosol at a pasture site and a rainforest site in the Amazon Basin, and present the first observations and characteristics of NPF commencing at ground level in the Amazon. No NPF occurred at the rainforest site. However, rain-enhanced intermediate ion bursts were frequent inside the forest canopy and raised ion concentrations by several orders of magnitude. To get a global overview of NPF, it is understandable that we select unambiguous NPF cases of each region for inter-comparison. In this work, however, we focused on unconventional NPF-related features, with the thesis that omitting these events may lead to oversights of potentially relevant processes to NPF. We conclude that by investigating the less-than-ideal cases, we can find new mechanisms and sources that allow us to better understand, quantify and predict the processes that lead to new particle formation.
Subject: Atmospheric Science
Rights: This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.

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