Distribution and Sources of Black Carbon in the Arctic

The Arctic is warming at twice the global rate over recent decades. To slow down this warming trend, there is growing interest in reducing the impact from short-lived climate forcers, such as black carbon (BC), because the benefits of mitigation are seen more quickly relative to CO2 reduction. To pr...

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Bibliographic Details
Main Author: Qi, Ling
Format: Doctoral or Postdoctoral Thesis
Language:English
Published: eScholarship, University of California 2016
Subjects:
Online Access:http://www.escholarship.org/uc/item/3mr3f0gn
id ftcdlib:qt3mr3f0gn
record_format openpolar
institution Open Polar
collection University of California: eScholarship
op_collection_id ftcdlib
language English
topic Atmospheric sciences
Atmospheric chemistry
Climate change
Arctic
black carbon
climate warming
source attribution
wet deposition
spellingShingle Atmospheric sciences
Atmospheric chemistry
Climate change
Arctic
black carbon
climate warming
source attribution
wet deposition
Qi, Ling
Distribution and Sources of Black Carbon in the Arctic
topic_facet Atmospheric sciences
Atmospheric chemistry
Climate change
Arctic
black carbon
climate warming
source attribution
wet deposition
description The Arctic is warming at twice the global rate over recent decades. To slow down this warming trend, there is growing interest in reducing the impact from short-lived climate forcers, such as black carbon (BC), because the benefits of mitigation are seen more quickly relative to CO2 reduction. To propose efficient mitigation policies, it is imperative to improve our understanding of BC distribution in the Arctic and to identify the sources. In this dissertation, we investigate the sensitivity of BC in the Arctic, including BC concentrations in snow (BCsnow) and BC concentrations in air (BCair), to emissions, dry deposition and wet scavenging using a global 3-D chemical transport model (CTM) GEOS-Chem. By including flaring emissions, estimating dry deposition velocity using resistance-in-series method, and including Wegener-Bergeron-Findeisen (WBF) in wet scavenging, simulated BCsnow in the eight Arctic sub-regions agree with the observations within a factor of two, and simulated BCair fall within the uncertainty range of observations. Specifically, we find that natural gas flaring emissions in Western Extreme North of Russia (WENR) strongly enhance BCsnow (by up to ∼50%) and BCair (by 20–32%) during snow season in the so-called ’Arctic front’, but has negligible impact on BC in the free troposphere. The updated dry deposition velocity over snow and ice is much larger than those used in most of global CTMs and agrees better with observation. The resulting BCsnow changes marginally because of the offsetting of higherdry and lower wet deposition fluxes. In contrast, surface BCair decreases strongly due to the faster dry deposition (by 27–68%). WBF occurs when the environmental vapor pressure is in between the saturation vapor pressure of ice crystals and water drops in mixed-phase clouds. As a result, water drops evaporate and releases BC particles in them back into the interstitial air. In most CTMs, WBF is either missing or represented by a uniform and low BC scavenging efficiency. In this dissertation, we relate WBF with temperature and ice mass fraction based on long-term observations in mixed-phase clouds. We find that WBF reduces BC scavenging efficiency globally, with larger decrease at higher latitude and altitude (from 8% in the tropics to 76% in the Arctic). WBF slows down and reduces wet deposition of BC and leave more BC in the atmosphere. Higher BCair results in larger dry deposition. The resulting total deposition is lower in mid-latitudes (by 12–34%) and higher in the Arctic (2–29%). Globally, including WBF significantly reduces the discrepancy of BCsnow (by ∼50%), BCair (by ∼50%), and washout ratios (by a factor of two to four). The remaining discrepancies in these variables suggest that in-cloud removal is likely still excessive over land. In the last part, we identify sources of surface atmospheric BC in the Arctic in springtime, when radiative forcing is the largest due to the high insolation and surface albedo. We find a large contribution from Asian anthropogenic sources (40–43%) and open biomass burning emissions from forest fires in South Siberia (29–41%). Outside the Arctic front, BC is strongly enhanced by episodic, direct transport events from Asia and Siberia after ∼12 days of transport. In contrast, in the Arctic front, a large fraction of the Asian contribution is in the form of ’chronic’ pollution on 1–2 month timescale. As such, it is likely that previous studies using 5- or 10-day trajectory analyses strongly underestimated the contribution from Asia to surface BC in the Arctic. Our results point toward an urgent need for better characterization of flaring emissions of BC (e.g. the emission factors, temporal and spatial distribution), extensive measurements of both the dry deposition of BC over snow and ice, and the scavenging efficiency of BC in mixed-phase clouds, particularly over Ocean. More measurements of 14C are needed to better understand sources of BC (fossil fuel combustion versus biomass burning) and to provide additional constrain on BC simulations.
format Doctoral or Postdoctoral Thesis
author Qi, Ling
author_facet Qi, Ling
author_sort Qi, Ling
title Distribution and Sources of Black Carbon in the Arctic
title_short Distribution and Sources of Black Carbon in the Arctic
title_full Distribution and Sources of Black Carbon in the Arctic
title_fullStr Distribution and Sources of Black Carbon in the Arctic
title_full_unstemmed Distribution and Sources of Black Carbon in the Arctic
title_sort distribution and sources of black carbon in the arctic
publisher eScholarship, University of California
publishDate 2016
url http://www.escholarship.org/uc/item/3mr3f0gn
op_coverage 164
geographic Arctic
geographic_facet Arctic
genre albedo
Arctic
Arctic
black carbon
Climate change
Extreme North of Russia
Siberia
genre_facet albedo
Arctic
Arctic
black carbon
Climate change
Extreme North of Russia
Siberia
op_source Qi, Ling. (2016). Distribution and Sources of Black Carbon in the Arctic. UCLA: Atmospheric & Oceanic Sciences 002E. Retrieved from: http://www.escholarship.org/uc/item/3mr3f0gn
op_relation http://www.escholarship.org/uc/item/3mr3f0gn
qt3mr3f0gn
op_rights public
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spelling ftcdlib:qt3mr3f0gn 2023-05-15T13:11:34+02:00 Distribution and Sources of Black Carbon in the Arctic Qi, Ling 164 2016-01-01 application/pdf http://www.escholarship.org/uc/item/3mr3f0gn en eng eScholarship, University of California http://www.escholarship.org/uc/item/3mr3f0gn qt3mr3f0gn public Qi, Ling. (2016). Distribution and Sources of Black Carbon in the Arctic. UCLA: Atmospheric & Oceanic Sciences 002E. Retrieved from: http://www.escholarship.org/uc/item/3mr3f0gn Atmospheric sciences Atmospheric chemistry Climate change Arctic black carbon climate warming source attribution wet deposition dissertation 2016 ftcdlib 2016-12-09T23:50:47Z The Arctic is warming at twice the global rate over recent decades. To slow down this warming trend, there is growing interest in reducing the impact from short-lived climate forcers, such as black carbon (BC), because the benefits of mitigation are seen more quickly relative to CO2 reduction. To propose efficient mitigation policies, it is imperative to improve our understanding of BC distribution in the Arctic and to identify the sources. In this dissertation, we investigate the sensitivity of BC in the Arctic, including BC concentrations in snow (BCsnow) and BC concentrations in air (BCair), to emissions, dry deposition and wet scavenging using a global 3-D chemical transport model (CTM) GEOS-Chem. By including flaring emissions, estimating dry deposition velocity using resistance-in-series method, and including Wegener-Bergeron-Findeisen (WBF) in wet scavenging, simulated BCsnow in the eight Arctic sub-regions agree with the observations within a factor of two, and simulated BCair fall within the uncertainty range of observations. Specifically, we find that natural gas flaring emissions in Western Extreme North of Russia (WENR) strongly enhance BCsnow (by up to ∼50%) and BCair (by 20–32%) during snow season in the so-called ’Arctic front’, but has negligible impact on BC in the free troposphere. The updated dry deposition velocity over snow and ice is much larger than those used in most of global CTMs and agrees better with observation. The resulting BCsnow changes marginally because of the offsetting of higherdry and lower wet deposition fluxes. In contrast, surface BCair decreases strongly due to the faster dry deposition (by 27–68%). WBF occurs when the environmental vapor pressure is in between the saturation vapor pressure of ice crystals and water drops in mixed-phase clouds. As a result, water drops evaporate and releases BC particles in them back into the interstitial air. In most CTMs, WBF is either missing or represented by a uniform and low BC scavenging efficiency. In this dissertation, we relate WBF with temperature and ice mass fraction based on long-term observations in mixed-phase clouds. We find that WBF reduces BC scavenging efficiency globally, with larger decrease at higher latitude and altitude (from 8% in the tropics to 76% in the Arctic). WBF slows down and reduces wet deposition of BC and leave more BC in the atmosphere. Higher BCair results in larger dry deposition. The resulting total deposition is lower in mid-latitudes (by 12–34%) and higher in the Arctic (2–29%). Globally, including WBF significantly reduces the discrepancy of BCsnow (by ∼50%), BCair (by ∼50%), and washout ratios (by a factor of two to four). The remaining discrepancies in these variables suggest that in-cloud removal is likely still excessive over land. In the last part, we identify sources of surface atmospheric BC in the Arctic in springtime, when radiative forcing is the largest due to the high insolation and surface albedo. We find a large contribution from Asian anthropogenic sources (40–43%) and open biomass burning emissions from forest fires in South Siberia (29–41%). Outside the Arctic front, BC is strongly enhanced by episodic, direct transport events from Asia and Siberia after ∼12 days of transport. In contrast, in the Arctic front, a large fraction of the Asian contribution is in the form of ’chronic’ pollution on 1–2 month timescale. As such, it is likely that previous studies using 5- or 10-day trajectory analyses strongly underestimated the contribution from Asia to surface BC in the Arctic. Our results point toward an urgent need for better characterization of flaring emissions of BC (e.g. the emission factors, temporal and spatial distribution), extensive measurements of both the dry deposition of BC over snow and ice, and the scavenging efficiency of BC in mixed-phase clouds, particularly over Ocean. More measurements of 14C are needed to better understand sources of BC (fossil fuel combustion versus biomass burning) and to provide additional constrain on BC simulations. Doctoral or Postdoctoral Thesis albedo Arctic Arctic black carbon Climate change Extreme North of Russia Siberia University of California: eScholarship Arctic