Title: Secondary organic aerosol formation in biomass-burning plumes: theoretical analysis of lab studies and ambient plumes

Abstract

Abstract. Secondary organic aerosol (SOA) has been shown to form in biomass-burning emissions in laboratory and field studies. However, there is significant variability among studies in mass enhancement, which could be due to differences in fuels, fire conditions, dilution, and/or limitations of laboratory experiments and observations. This study focuses on understanding processes affecting biomass-burning SOA formation in laboratory smog-chamber experiments and in ambient plumes. Vapor wall losses have been demonstrated to be an important factor that can suppress SOA formation in laboratory studies of traditional SOA precursors; however, impacts of vapor wall losses on biomass-burning SOA have not yet been investigated. We use an aerosol-microphysical model that includes representations of volatility and oxidation chemistry to estimate the influence of vapor wall loss on SOA formation observed in the FLAME III smog-chamber studies. Our simulations with base-case assumptions for chemistry and wall loss predict a mean OA mass enhancement (the ratio of final to initial OA mass, corrected for particle-phase wall losses) of 1.8 across all experiments when vapor wall losses are modeled, roughly matching the mean observed enhancement during FLAME III. The mean OA enhancement increases to over 3 when vapor wall losses are turned off, implying that vapor wall losses reducemore » the apparent SOA formation. We find that this decrease in the apparent SOA formation due to vapor wall losses is robust across the ranges of uncertainties in the key model assumptions for wall-loss and mass-transfer coefficients and chemical mechanisms.We then apply similar assumptions regarding SOA formation chemistry and physics to smoke emitted into the atmosphere. In ambient plumes, the plume dilution rate impacts the organic partitioning between the gas and particle phases, which may impact the potential for SOA to form as well as the rate of SOA formation. We add Gaussian dispersion to our aerosol-microphysical model to estimate how SOA formation may vary under different ambient-plume conditions (e.g., fire size, emission mass flux, atmospheric stability). Smoke from small fires, such as typical prescribed burns, dilutes rapidly, which drives evaporation of organic vapor from the particle phase, leading to more effective SOA formation. Emissions from large fires, such as intense wildfires, dilute slowly, suppressing OA evaporation and subsequent SOA formation in the near field. We also demonstrate that different approaches to the calculation of OA enhancement in ambient plumes can lead to different conclusions regarding SOA formation. OA mass enhancement ratios of around 1 calculated using an inert tracer, such as black carbon or CO, have traditionally been interpreted as exhibiting little or no SOA formation; however, we show that SOA formation may have greatly contributed to the mass in these plumes.In comparison of laboratory and plume results, the possible inconsistency of OA enhancement between them could be in part attributed to the effect of chamber walls and plume dilution. Our results highlight that laboratory and field experiments that focus on the fuel and fire conditions also need to consider the effects of plume dilution or vapor losses to walls.« less

Authors:

Bian, Qijing ;

• Search DOE PAGES for author "Bian, Qijing"
• Search DOE PAGES for ORCID "0000-0002-1511-9026"

Jathar, Shantanu H. ;

• Search DOE PAGES for author "Jathar, Shantanu H."
• Search DOE PAGES for ORCID "0000-0003-4106-2358"

Kodros, John K.; Barsanti, Kelley C. ;

• Search DOE PAGES for author "Barsanti, Kelley C."
• Search DOE PAGES for ORCID "0000-0002-6065-8643"

Hatch, Lindsay E.; May, Andrew A. ;

• Search DOE PAGES for author "May, Andrew A."
• Search DOE PAGES for ORCID "0000-0001-7908-8815"

Kreidenweis, Sonia M. ;

• Search DOE PAGES for author "Kreidenweis, Sonia M."
• Search DOE PAGES for ORCID "0000-0002-2561-2914"

Pierce, Jeffrey R.

• Search DOE PAGES for author "Pierce, Jeffrey R."
• Search DOE PAGES for ORCID "0000-0002-4241-838X"

Publication Date:

Fri Apr 28 00:00:00 EDT 2017

Research Org.:

Univ. of Colorado, Boulder, CO (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:

1353515

Alternate Identifier(s):

OSTI ID: 1368356

Grant/Contract Number:  

SC0006035; R833747; R834554

Resource Type:

Published Article

Journal Name:

Atmospheric Chemistry and Physics (Online)

Additional Journal Information:

Journal Name: Atmospheric Chemistry and Physics (Online) Journal Volume: 17 Journal Issue: 8; Journal ID: ISSN 1680-7324

Publisher:

Copernicus Publications, EGU

Country of Publication:

Germany

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES