Satellite observations of aerosol transport from East Asia to the Arctic: three case studies

Abstract. Vertical profiles of aerosols obtained with the CALIOP lidar onboard CALIPSO are used in conjunction with the GEOS-Chem chemical transport model and NOAA's HYSPLIT trajectory model to document three aerosol export events from East Asia to the Arctic that occurred in the year 2007. During each of these events CALIOP sampled the pollution plumes multiple times over periods of five to seven days. Meridional transport to the Arctic was rapid, taking 3–4 days and was accompanied by net diabatic heating of ~5 °C/day and precipitation in its ascending stage. Once in the Arctic transport was nearly isentropic with slow subsidence and radiative cooling at a rate of 1–1.5 °C/day. We find close agreement between modeled and observed plume in terms of length, altitude, thickness and, within the measurement uncertainties, extinction coefficient. In one event the satellite algorithm misclassifies the aerosol layer as ice clouds as a result of the relatively high depolarization ratio (0.06), likely caused by a somewhat high dust component in the aerosol mixture. The misclassification is more severe at daytime (67% of layers are misclassified) than at nighttime (32%). The two most intense export events occurred in early spring within a three-week time span and are strongly related to a persisting blocking anticyclone that was located in the NW Pacific. Using 500 hPa geopotential height anomalies of these two events along with several others in 2007–2009 we develop a meteorological index that captures 40–60% of the variance of Asian transport events to the Arctic in winter and spring.

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Satellite observations of aerosol transport from East Asia to the Arctic: three case studies

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-2225-2011 ◽

2011 ◽

Vol 11 (5) ◽

pp. 2225-2243 ◽

Cited By ~ 30

Author(s):

M. Di Pierro ◽

L. Jaeglé ◽

T. L. Anderson

Keyword(s):

East Asia ◽

Transport Model ◽

The Arctic ◽

Aerosol Layer ◽

Chemical Transport Model ◽

Maximum Probability ◽

Meridional Transport ◽

Pressure System ◽

Blocking High ◽

Dust Component

Abstract. Vertical profiles of aerosol extinction obtained with the CALIOP lidar onboard CALIPSO are used in conjunction with the GEOS-Chem chemical transport model and NOAA's HYSPLIT trajectory model to document three aerosol export events from East Asia to the Arctic in the year 2007. During each of these events CALIOP sampled the pollution plumes multiple times over periods of five to seven days. Midlatitude cyclones lifted the pollution to the free troposphere with net diabatic heating of ~5 °C day−1 and precipitation in this initial ascending stage. Rapid meridional transport to the Arctic took place at 3–7 km altitude, and was mediated by either a blocking high pressure system in the NW Pacific or a trough-ridge configuration. Once in the Arctic transport was nearly isentropic with slow subsidence and radiative cooling at a rate of 1–1.5 °C day−1. We find good agreement between modeled and observed plumes in terms of length, altitude, thickness and, within the measurement uncertainties, extinction coefficient. In one event the satellite algorithm misclassifies the aerosol layer as ice clouds as a result of the relatively high depolarization ratio (0.06), likely caused by a high dust component in the aerosol mixture. Using 500 hPa geopotential height anomalies for these three events along with eight other export events observed by CALIOP in 2007–2009, we develop a meteorological index that captures 40–60% of the variance of Asian transport events to the Arctic in winter and spring. Simulations with the GEOS-Chem model show that 6 major export events from Asia to the Arctic occur each year, on average. The maximum probability for such events is during March–June, with a secondary maximum in October–November. During these events, Asian pollution and dust aerosols account for 50–70% of the aerosol optical depth over the Siberian sector of the Arctic, compared to a mean background contribution of 33%.

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Composite study of aerosol export events from East Asia and North America

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-21977-2012 ◽

2012 ◽

Vol 12 (8) ◽

pp. 21977-22022 ◽

Cited By ~ 1

Author(s):

Y. Luan ◽

L. Jaeglé

Keyword(s):

Boundary Layer ◽

North America ◽

East Asia ◽

Transport Model ◽

Lower Troposphere ◽

Temporal Variations ◽

The Arctic ◽

Chemical Transport Model ◽

Mean Values ◽

Warm Conveyor Belts

Abstract. We use satellite observations of aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectrometer (MODIS) together with the GEOS-Chem global chemical transport model to contrast export of aerosols from East Asia and North America during 2004–2010. The GEOS-Chem model reproduces the spatial distribution and temporal variations of Asian aerosol outflow generally well, although a low bias (−30%) is found in the model fine mode AOD. We use the model to identify 244 aerosol pollution export events from E. Asia and 251 export events from N. America over our 7-yr study period. When these events are composited by season, we find that the AOD in the outflow is enhanced by 50–100% relative to seasonal mean values. The composite Asian plume splits into one branch going poleward towards the Arctic, with the other crossing the Pacific in 6–8 days. A fraction of the aerosols is trapped in the subtropical Pacific High. The N. American plume travels to the northeast Atlantic, reaching Europe after 4–5 days. Part of the composite plume turns anticyclonically in the Azores High, where it slowly decays. Both the Asian and N. American export events are favored by a dipole structure in sea-level pressure anomalies, associated with mid-latitude cyclone activity over the respective source regions. The observed AOD in the E. Asian outflow exhibits stronger seasonality, with a spring maximum, than the N. American outflow, with a weak summer maximum. The large spring AOD in the Asian outflow is the result of enhanced sulfate and dust aerosol concentrations, but is also due to a larger export efficiency of sulfate and SO2 from the Asian boundary layer relative to the N. American boundary layer. While the N. American sulfate outflow is mostly found in the lower troposphere (1–3 km altitude), the Asian sulfate outflow occurs at higher altitudes (2–6 km). In the Asian outflow 42–59% of the sulfate column is present above 2 km altitude, with only 24–35% in the N. American outflow. We link this to the factor of 2–5 lower precipitation in the warm conveyor belts (WCB) of midlatitude cyclones over E. Asia compared to N. America. This relative lack of precipitation makes Asian WCB very efficient for injecting aerosols in the middle troposphere.

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Composite study of aerosol export events from East Asia and North America

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-1221-2013 ◽

2013 ◽

Vol 13 (3) ◽

pp. 1221-1242 ◽

Cited By ~ 11

Author(s):

Y. Luan ◽

L. Jaeglé

Keyword(s):

Boundary Layer ◽

North America ◽

East Asia ◽

Transport Model ◽

Lower Troposphere ◽

Temporal Variations ◽

The Arctic ◽

Chemical Transport Model ◽

Mean Values ◽

Dipole Structure

Abstract. We use satellite observations of aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectrometer (MODIS) together with the GEOS-Chem global chemical transport model to contrast export of aerosols from East Asia and North America during 2004–2010. The GEOS-Chem model reproduces the spatial distribution and temporal variations of Asian aerosol outflow generally well, although a low bias (−30%) is found in the model fine mode AOD, particularly during summer. We use the model to identify 244 aerosol pollution export events from E. Asia and 251 export events from N. America over our 7-year study period. When these events are composited by season, we find that the AOD in the outflow is enhanced by 50–100% relative to seasonal mean values. The composite Asian plume splits into one branch going poleward to the Arctic in 3–4 days, with the other crossing the Pacific Ocean in 6–8 days. A fraction of the aerosols is trapped in the subtropical Pacific High during spring and summer. The N. American plume travels to the northeast Atlantic, reaching Europe after 4–5 days. Part of the composite plume turns anticyclonically in the Azores High, where it slowly decays. Both the Asian and N. American export events are favored by a dipole structure in sea-level pressure anomalies, associated with mid-latitude cyclone activity over the respective source regions. This dipole structure during outflow events is a strong feature for all seasons except summer, when convection becomes more important. The observed AOD in the E. Asian outflow exhibits stronger seasonality, with a spring maximum, than the N. American outflow, with a broad spring/summer maximum. The large spring AOD in the Asian outflow is the result of enhanced sulfate and dust aerosol concentrations, but is also due to a larger export efficiency of sulfate and SO2 from the Asian boundary layer relative to the N. American boundary layer. While the N. American sulfate outflow is mostly found in the lower troposphere (1–3 km altitude), the Asian sulfate outflow occurs at higher altitudes (2–6 km). In the Asian outflow 42–59% of the sulfate column is present above 2 km altitude, with only 24–35% in the N. American outflow. We link this to the factor of 2–5 lower precipitation in the warm conveyor belts (WCB) of midlatitude cyclones over E. Asia compared to N. America. This relative lack of precipitation makes Asian WCB very efficient for injecting aerosols in the middle troposphere.

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Record springtime stratospheric ozone depletion at 80°N in 2020

10.5194/egusphere-egu21-8892 ◽

2021 ◽

Author(s):

Ramina Alwarda ◽

Kristof Bognar ◽

Kimberly Strong ◽

Martyn Chipperfield ◽

Sandip Dhomse ◽

...

Keyword(s):

Ozone Depletion ◽

Transport Model ◽

Stratospheric Ozone ◽

Polar Vortex ◽

The Arctic ◽

Optical Absorption Spectroscopy ◽

Chemical Transport Model ◽

Polar Stratospheric Clouds ◽

Ozone Loss ◽

Stratospheric Clouds

The Arctic winter of 2019-2020 was characterized by an unusually persistent polar vortex and temperatures in the lower stratosphere that were consistently below the threshold for the formation of polar stratospheric clouds (PSCs). These conditions led to ozone loss that is comparable to the Antarctic ozone hole. Ground-based measurements from a suite of instruments at the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka, Canada (80.05&#176;N, 86.42&#176;W) were used to investigate chemical ozone depletion. The vortex was located above Eureka longer than in any previous year in the 20-year dataset and lidar measurements provided evidence of polar stratospheric clouds (PSCs) above Eureka. Additionally, UV-visible zenith-sky Differential Optical Absorption Spectroscopy (DOAS) measurements showed record ozone loss in the 20-year dataset, evidence of denitrification along with the slowest increase of NO2 during spring, as well as enhanced reactive halogen species (OClO and BrO). Complementary measurements of HCl and ClONO2 (chlorine reservoir species) from a Fourier transform infrared (FTIR) spectrometer showed unusually low columns that were comparable to 2011, the previous year with significant chemical ozone depletion. Record low values of HNO3 in the FTIR dataset are in accordance with the evidence of PSCs and a denitrified atmosphere. Estimates of chemical ozone loss were derived using passive ozone from the SLIMCAT offline chemical transport model to account for dynamical contributions to the stratospheric ozone budget.

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Record-breaking ozone loss in the Arctic winter 2010/2011: comparison with 1996/1997

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-7073-2012 ◽

2012 ◽

Vol 12 (15) ◽

pp. 7073-7085 ◽

Cited By ~ 34

Author(s):

J. Kuttippurath ◽

S. Godin-Beekmann ◽

F. Lefèvre ◽

G. Nikulin ◽

M. L. Santee ◽

...

Keyword(s):

Transport Model ◽

Chemical Transport ◽

The Arctic ◽

Altitude Range ◽

Chemical Transport Model ◽

Model Simulations ◽

Ozone Loss ◽

Elevated Ozone ◽

Record Value ◽

First Time

Abstract. We present a detailed discussion of the chemical and dynamical processes in the Arctic winters 1996/1997 and 2010/2011 with high resolution chemical transport model (CTM) simulations and space-based observations. In the Arctic winter 2010/2011, the lower stratospheric minimum temperatures were below 195 K for a record period of time, from December to mid-April, and a strong and stable vortex was present during that period. Simulations with the Mimosa-Chim CTM show that the chemical ozone loss started in early January and progressed slowly to 1 ppmv (parts per million by volume) by late February. The loss intensified by early March and reached a record maximum of ~2.4 ppmv in the late March–early April period over a broad altitude range of 450–550 K. This coincides with elevated ozone loss rates of 2–4 ppbv sh−1 (parts per billion by volume/sunlit hour) and a contribution of about 30–55% and 30–35% from the ClO-ClO and ClO-BrO cycles, respectively, in late February and March. In addition, a contribution of 30–50% from the HOx cycle is also estimated in April. We also estimate a loss of about 0.7–1.2 ppmv contributed (75%) by the NOx cycle at 550–700 K. The ozone loss estimated in the partial column range of 350–550 K exhibits a record value of ~148 DU (Dobson Unit). This is the largest ozone loss ever estimated in the Arctic and is consistent with the remarkable chlorine activation and strong denitrification (40–50%) during the winter, as the modeled ClO shows ~1.8 ppbv in early January and ~1 ppbv in March at 450–550 K. These model results are in excellent agreement with those found from the Aura Microwave Limb Sounder observations. Our analyses also show that the ozone loss in 2010/2011 is close to that found in some Antarctic winters, for the first time in the observed history. Though the winter 1996/1997 was also very cold in March–April, the temperatures were higher in December–February, and, therefore, chlorine activation was moderate and ozone loss was average with about 1.2 ppmv at 475–550 K or 42 DU at 350–550 K, as diagnosed from the model simulations and measurements.

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Effects of Wegener-Bergeron-Findeisen Process on Global Black Carbon Distribution

10.5194/acp-2016-706 ◽

2016 ◽

Cited By ~ 1

Author(s):

Ling Qi ◽

Qinbin Li ◽

Cenlin He ◽

Xin Wang ◽

Jianping Huang

Keyword(s):

Transport Model ◽

Liquid Water Content ◽

Mixed Phase ◽

The Arctic ◽

Deposition Flux ◽

Chemical Transport Model ◽

Washout Ratio ◽

Lower Temperature ◽

Mixed Phase Clouds ◽

Scavenging Efficiency

Abstract. We systematically investigate the effects of Wegener-Bergeron-Findeisen (WBF) on BC scavenging efficiency, surface BCair, deposition flux, concentration in snow (BCsnow, ng g−1), and washout ratio using a global 3D chemical transport model (GEOS-Chem). We differentiate riming- versus WBF-dominated in-cloud scavenging based on liquid water content (LWC) and temperature. Specifically, we relate WBF to either temperature or ice mass fraction (IMF) in mixed-phase clouds. We find that at Jungfraujoch, Switzerland and Abisko, Sweden, where WBF dominates, the discrepancies of simulated BC scavenging efficiency and washout ratio are significantly reduced (from a factor of 3 to 10 % and from a factor of 4–5 to a factor of two). However, at Zeppelin, Norway, where riming dominates, simulation of BC scavenging efficiency, BCair, and washout ratio become worse (relative to observations) when WBF is included. There is thus an urgent need for extensive observations to distinguish and characterize riming- versus WBF-dominated aerosol scavenging in mixed-phase clouds and the associated BC scavenging efficiency. We find the reduction resulting from WBF to global BC scavenging efficiency varies substantially, from 8 % in the tropics to 76 % in the Arctic. The resulting annual mean BCair increases by up to 156 % at high altitudes and at northern high latitudes because of lower temperature and higher IMF. Overall, WBF halves the model-observation discrepancy (from −65 % to −30 %) of BCair across North America, Europe, China and the Arctic. Globally WBF increases BC burden from 0.22 to 0.29–0.35 mg m−2 yr−1, which partially explains the gap between observed and previous model simulated BC burdens over land. In addition, WBF significantly increases BC lifetime from 5.7 days to ~8 days. Additionally, WBF results in a significant redistribution of BC deposition in source and remote regions. Specifically, it lowers BC wet deposition (by 37–63 % at northern mid-latitudes and by 21–29 % in the Arctic) while increases dry deposition (by 3–16 % at mid-latitudes and by 81–159 % in the Arctic). The resulting total BC deposition is lower at mid-latitudes (by 12–34 %) but higher in the Arctic (by 2–29 %). We find that WBF decreases BCsnow at mid-latitudes (by ~15 %) but increases it in the Arctic (by 26 %) while improving model comparisons with observations. In addition, WBF dramatically reduces the model-observation discrepancy of washout ratios in winter (from a factor of 16 to 4). The remaining discrepancies in BCair, BCsnow and BC washout ratios suggest that in-cloud removal in mixed-phased clouds is likely still excessive over land.

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Do contemporary (1980–2015) emissions determine the elemental carbon deposition trend at Holtedahlfonna glacier, Svalbard?

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-12779-2017 ◽

2017 ◽

Vol 17 (20) ◽

pp. 12779-12795 ◽

Cited By ~ 5

Author(s):

Meri M. Ruppel ◽

Joana Soares ◽

Jean-Charles Gallet ◽

Elisabeth Isaksson ◽

Tõnu Martma ◽

...

Keyword(s):

Elemental Carbon ◽

Transport Model ◽

Ice Core ◽

Climate Impact ◽

The Arctic ◽

Chemical Transport Model ◽

Atmospheric Measurements ◽

Atmospheric Concentration ◽

Scavenging Efficiency ◽

Firn Core

Abstract. The climate impact of black carbon (BC) is notably amplified in the Arctic by its deposition, which causes albedo decrease and subsequent earlier snow and ice spring melt. To comprehensively assess the climate impact of BC in the Arctic, information on both atmospheric BC concentrations and deposition is essential. Currently, Arctic BC deposition data are very scarce, while atmospheric BC concentrations have been shown to generally decrease since the 1990s. However, a 300-year Svalbard ice core showed a distinct increase in EC (elemental carbon, proxy for BC) deposition from 1970 to 2004 contradicting atmospheric measurements and modelling studies. Here, our objective was to decipher whether this increase has continued in the 21st century and to investigate the drivers of the observed EC deposition trends. For this, a shallow firn core was collected from the same Svalbard glacier, and a regional-to-meso-scale chemical transport model (SILAM) was run from 1980 to 2015. The ice and firn core data indicate peaking EC deposition values at the end of the 1990s and lower values thereafter. The modelled BC deposition results generally support the observed glacier EC variations. However, the ice and firn core results clearly deviate from both measured and modelled atmospheric BC concentration trends, and the modelled BC deposition trend shows variations seemingly independent from BC emission or atmospheric BC concentration trends. Furthermore, according to the model ca. 99 % BC mass is wet-deposited at this Svalbard glacier, indicating that meteorological processes such as precipitation and scavenging efficiency have most likely a stronger influence on the BC deposition trend than BC emission or atmospheric concentration trends. BC emission source sectors contribute differently to the modelled atmospheric BC concentrations and BC deposition, which further supports our conclusion that different processes affect atmospheric BC concentration and deposition trends. Consequently, Arctic BC deposition trends should not directly be inferred based on atmospheric BC measurements, and more observational BC deposition data are required to assess the climate impact of BC in Arctic snow.

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Source attribution of Arctic black carbon constrained by aircraft and surface measurements

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-11971-2017 ◽

2017 ◽

Vol 17 (19) ◽

pp. 11971-11989 ◽

Cited By ~ 30

Author(s):

Jun-Wei Xu ◽

Randall V. Martin ◽

Andrew Morrow ◽

Sangeeta Sharma ◽

Lin Huang ◽

...

Keyword(s):

North America ◽

Biomass Burning ◽

Western Siberia ◽

Transport Model ◽

Chemical Transport ◽

The Arctic ◽

Anthropogenic Emissions ◽

Chemical Transport Model ◽

Northern Asia ◽

Airborne Measurements

Abstract. Black carbon (BC) contributes to Arctic warming, yet sources of Arctic BC and their geographic contributions remain uncertain. We interpret a series of recent airborne (NETCARE 2015; PAMARCMiP 2009 and 2011 campaigns) and ground-based measurements (at Alert, Barrow and Ny-Ålesund) from multiple methods (thermal, laser incandescence and light absorption) with the GEOS-Chem global chemical transport model and its adjoint to attribute the sources of Arctic BC. This is the first comparison with a chemical transport model of refractory BC (rBC) measurements at Alert. The springtime airborne measurements performed by the NETCARE campaign in 2015 and the PAMARCMiP campaigns in 2009 and 2011 offer BC vertical profiles extending to above 6 km across the Arctic and include profiles above Arctic ground monitoring stations. Our simulations with the addition of seasonally varying domestic heating and of gas flaring emissions are consistent with ground-based measurements of BC concentrations at Alert and Barrow in winter and spring (rRMSE  < 13 %) and with airborne measurements of the BC vertical profile across the Arctic (rRMSE  = 17 %) except for an underestimation in the middle troposphere (500–700 hPa).Sensitivity simulations suggest that anthropogenic emissions in eastern and southern Asia have the largest effect on the Arctic BC column burden both in spring (56 %) and annually (37 %), with the largest contribution in the middle troposphere (400–700 hPa). Anthropogenic emissions from northern Asia contribute considerable BC (27 % in spring and 43 % annually) to the lower troposphere (below 900 hPa). Biomass burning contributes 20 % to the Arctic BC column annually.At the Arctic surface, anthropogenic emissions from northern Asia (40–45 %) and eastern and southern Asia (20–40 %) are the largest BC contributors in winter and spring, followed by Europe (16–36 %). Biomass burning from North America is the most important contributor to all stations in summer, especially at Barrow.Our adjoint simulations indicate pronounced spatial heterogeneity in the contribution of emissions to the Arctic BC column concentrations, with noteworthy contributions from emissions in eastern China (15 %) and western Siberia (6.5 %). Although uncertain, gas flaring emissions from oilfields in western Siberia could have a striking impact (13 %) on Arctic BC loadings in January, comparable to the total influence of continental Europe and North America (6.5 % each in January). Emissions from as far as the Indo-Gangetic Plain could have a substantial influence (6.3 % annually) on Arctic BC as well.

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Boundary layer and free-tropospheric dimethyl sulfide in the Arctic spring and summer

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-8757-2017 ◽

2017 ◽

Vol 17 (14) ◽

pp. 8757-8770 ◽

Cited By ~ 3

Author(s):

Roghayeh Ghahremaninezhad ◽

Ann-Lise Norman ◽

Betty Croft ◽

Randall V. Martin ◽

Jeffrey R. Pierce ◽

...

Keyword(s):

Dimethyl Sulfide ◽

Transport Model ◽

Dispersion Model ◽

Open Water ◽

Particle Dispersion ◽

The Arctic ◽

Chemical Transport Model ◽

Model Simulations ◽

Baffin Bay ◽

Mixing Ratios

Abstract. Vertical distributions of atmospheric dimethyl sulfide (DMS(g)) were sampled aboard the research aircraft Polar 6 near Lancaster Sound, Nunavut, Canada, in July 2014 and on pan-Arctic flights in April 2015 that started from Longyearbyen, Spitzbergen, and passed through Alert and Eureka, Nunavut, and Inuvik, Northwest Territories. Larger mean DMS(g) mixing ratios were present during April 2015 (campaign mean of 116 ± 8 pptv) compared to July 2014 (campaign mean of 20 ± 6 pptv). During July 2014, the largest mixing ratios were found near the surface over the ice edge and open water. DMS(g) mixing ratios decreased with altitude up to about 3 km. During April 2015, profiles of DMS(g) were more uniform with height and some profiles showed an increase with altitude. DMS reached as high as 100 pptv near 2500 m. Relative to the observation averages, GEOS-Chem (www.geos-chem.org) chemical transport model simulations were higher during July and lower during April. Based on the simulations, more than 90 % of the July DMS(g) below 2 km and more than 90 % of the April DMS(g) originated from Arctic seawater (north of 66° N). During April, 60 % of the DMS(g), between 500 and 3000 m originated from Arctic seawater. During July 2014, FLEXPART (FLEXible PARTicle dispersion model) simulations locate the sampled air mass over Baffin Bay and the Canadian Arctic Archipelago 4 days back from the observations. During April 2015, the locations of the air masses 4 days back from sampling were varied: Baffin Bay/Canadian Archipelago, the Arctic Ocean, Greenland and the Pacific Ocean. Our results highlight the role of open water below the flight as the source of DMS(g) during July 2014 and the influence of long-range transport (LRT) of DMS(g) from further afield in the Arctic above 2500 m during April 2015.

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Pollution transport from North America to Greenland during summer 2008

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-3825-2013 ◽

2013 ◽

Vol 13 (7) ◽

pp. 3825-3848 ◽

Cited By ~ 30

Author(s):

J. L. Thomas ◽

J.-C. Raut ◽

K. S. Law ◽

L. Marelle ◽

G. Ancellet ◽

...

Keyword(s):

North America ◽

Transport Model ◽

Ozone Production ◽

The Arctic ◽

Pollution Transport ◽

Chemical Transport Model ◽

Fire Emissions ◽

Fire Plumes ◽

Ozone Levels ◽

Pollution Plumes

Abstract. Ozone pollution transported to the Arctic is a significant concern because of the rapid, enhanced warming in high northern latitudes, which is caused, in part, by short-lived climate forcers, such as ozone. Long-range transport of pollution contributes to background and episodic ozone levels in the Arctic. However, the extent to which plumes are photochemically active during transport, particularly during the summer, is still uncertain. In this study, regional chemical transport model simulations are used to examine photochemical production of ozone in air masses originating from boreal fire and anthropogenic emissions over North America and during their transport toward the Arctic during early July 2008. Model results are evaluated using POLARCAT aircraft data collected over boreal fire source regions in Canada (ARCTAS-B) and several days downwind over Greenland (POLARCAT-France and POLARCAT-GRACE). Model results are generally in good agreement with the observations, except for certain trace gas species over boreal fire regions, in some cases indicating that the fire emissions are too low. Anthropogenic and biomass burning pollution (BB) from North America was rapidly uplifted during transport east and north to Greenland where pollution plumes were observed in the mid- and upper troposphere during POLARCAT. A model sensitivity study shows that CO levels are in better agreement with POLARCAT measurements (fresh and aged fire plumes) upon doubling CO emissions from fires. Analysis of model results, using ΔO3/ΔCO enhancement ratios, shows that pollution plumes formed ozone during transport towards the Arctic. Fresh anthropogenic plumes have average ΔO3/ΔCO enhancement ratios of 0.63 increasing to 0.92 for aged anthropogenic plumes, indicating additional ozone production during aging. Fresh fire plumes are only slightly enhanced in ozone (ΔO3/ΔCO=0.08), but form ozone downwind with ΔO3/ΔCO of 0.49 for aged BB plumes (model-based run). We estimate that aged anthropogenic and BB pollution together made an important contribution to ozone levels with an average contribution for latitudes >55° N of up to 6.5 ppbv (18%) from anthropogenic pollution and 3 ppbv (5.2%) from fire pollution in the model domain in summer 2008.

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