scholarly journals Quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS) experiment: design, execution and science overview

2013 ◽  
Vol 13 (13) ◽  
pp. 6239-6261 ◽  
Author(s):  
P. I. Palmer ◽  
M. Parrington ◽  
J. D. Lee ◽  
A. C. Lewis ◽  
A. R. Rickard ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Forest Fires ◽  
Atmospheric Composition ◽  
Atmospheric Measurements ◽  
Eastern Canada ◽  
Chemical Aging ◽  
Air Masses ◽  
Research Aircraft ◽  
The Uk ◽  
The Impact

Abstract. We describe the design and execution of the BORTAS (Quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites) experiment, which has the overarching objective of understanding the chemical aging of air masses that contain the emission products from seasonal boreal wildfires and how these air masses subsequently impact downwind atmospheric composition. The central focus of the experiment was a two-week deployment of the UK BAe-146-301 Atmospheric Research Aircraft (ARA) over eastern Canada, based out of Halifax, Nova Scotia. Atmospheric ground-based and sonde measurements over Canada and the Azores associated with the planned July 2010 deployment of the ARA, which was postponed by 12 months due to UK-based flights related to the dispersal of material emitted by the Eyjafjallajökull volcano, went ahead and constituted phase A of the experiment. Phase B of BORTAS in July 2011 involved the same atmospheric measurements, but included the ARA, special satellite observations and a more comprehensive ground-based measurement suite. The high-frequency aircraft data provided a comprehensive chemical snapshot of pyrogenic plumes from wildfires, corresponding to photochemical (and physical) ages ranging from < 1 day to ~

scholarly journals Quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS) experiment: design, execution and science overview

2013 ◽  
Vol 13 (2) ◽  
pp. 4127-4181 ◽  
Author(s):  
P. I. Palmer ◽  
M. Parrington ◽  
J. D. Lee ◽  
A. C. Lewis ◽  
A. R. Rickard ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Atmospheric Chemistry ◽  
Forest Fires ◽  
Atmospheric Transport ◽  
Chemical Mechanism ◽  
Atmospheric Composition ◽  
Limited Information ◽  
Eastern Canada ◽  
The Impact ◽  
Aircraft Data

Abstract. We describe the design and execution of the BORTAS (Quantifying the impact of BOReal forest fires on Tropospheric oxidants using Aircraft and Satellites) experiment, which has the overarching objective of understanding the chemical aging of airmasses that contain the emission products from seasonal boreal wildfires and how these airmasses subsequently impact downwind atmospheric composition. The central focus of the experiment was a two-week deployment of the UK BAe-146-301 Atmospheric Research Aircraft (ARA) over eastern Canada. The planned July 2010 deployment of the ARA was postponed by 12 months because of activities related to the dispersal of material emitted by the Eyjafjallajökull volcano. However, most other planned model and measurement activities, including ground-based measurements at the Dalhousie University Ground Station (DGS), enhanced ozonesonde launches, and measurements at the Pico Atmospheric Observatory in the Azores, went ahead and constituted phase A of the experiment. Phase B of BORTAS in July 2011 included the same measurements, but included the ARA, special satellite observations and a more comprehensive measurement suite at the DGS. The high-frequency aircraft data provided a comprehensive snapshot of the pyrogenic plumes from wildfires. The coordinated ground-based and sonde data provided detailed but spatially-limited information that put the aircraft data into context of the longer burning season. We coordinated aircraft vertical profiles and overpasses of the NASA Tropospheric Emission Spectrometer and the Canadian Atmospheric Chemistry Experiment. These space-borne data, while less precise than other data, helped to relate the two-week measurement campaign to larger geographical and longer temporal scales. We interpret these data using a range of chemistry models: from a near-explicit gas-phase chemical mechanism, which tests out understanding of the underlying chemical mechanism, to regional and global 3-D models of atmospheric transport and lumped chemistry, which helps to assess the performance of the simplified chemical mechanism and effectively act as intermediaries between different measurement types. We also present an overview of some of the new science that has originated from this project from the mission planning and execution to the analysis of the ground-based, aircraft, and space-borne data.

scholarly journals ACE-FTS observations of pyrogenic trace species in boreal biomass burning plumes during BORTAS

2012 ◽  
Vol 12 (12) ◽  
pp. 31629-31661 ◽  
Author(s):  
K. A. Tereszchuk ◽  
G. González Abad ◽  
C. Clerbaux ◽  
J. Hadji-Lazaro ◽  
D. Hurtmans ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Biomass Burning ◽  
Atmospheric Chemistry ◽  
Forest Fires ◽  
Atmospheric Composition ◽  
Fire Season ◽  
Satellite Measurement ◽  
Mixing Ratios ◽  
Trace Species ◽  
The Impact

Abstract. To further our understanding of the effects of biomass burning emissions on atmospheric composition, the Quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS) campaign was conducted on 12 July to 3 August 2011 during the Boreal forest fire season in Canada. The simultaneous aerial, ground and satellite measurement campaign sought to record instances of Boreal biomass burning to measure the tropospheric volume mixing ratios (VMRs) of short- and long-lived trace molecular species from biomass burning emissions. The goal was to investigate the connection between the composition and the distribution of these pyrogenic outflows and their resulting perturbation to atmospheric chemistry, with particular focus on oxidant species to determine the overall impact on the oxidizing capacity of the free troposphere. Measurements of pyrogenic trace species in Boreal biomass burning plumes were made by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) onboard the Canadian Space Agency (CSA) SCISAT-1 satellite during the BORTAS campaign. Even though most biomass burning smoke is typically confined to the boundary layer, emissions are often injected directly into the upper troposphere via fire-related convective processes, thus allowing space-borne instruments to measure these pyrogenic outflows. An extensive set of 15 molecules, CH3OH, CH4, C2H2, C2H6, C3H6O, CO, HCN, HCOOH, HNO3, H2CO, NO, NO2, OCS, O3 and PAN have been analyzed. Included in this analysis is the calculation of age-dependent sets of enhancement ratios for each of the species.

scholarly journals A case study of aerosol depletion in a biomass burning plume over Eastern Canada during the 2011 BORTAS field experiment

2014 ◽  
Vol 14 (3) ◽  
pp. 3395-3426 ◽  
Author(s):  
J. E. Franklin ◽  
J. R. Drummond ◽  
D. Griffin ◽  
J. R. Pierce ◽  
D. L. Waugh ◽  
...  
Keyword(s):  
Long Range ◽  
Biomass Burning ◽  
Forest Fires ◽  
Particulate Material ◽  
Trace Gas ◽  
Eastern Canada ◽  
Air Masses ◽  
Chemical Behaviour ◽  
Physical And Chemical ◽  
The Impact

Abstract. We present measurements of a long range smoke transport event recorded on 20–21 July 2011 over Halifax, Nova Scotia, Canada, during the Quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS-B) campaign. Ground-based Fourier transform spectrometers and photometers detected air masses associated with large wildland fires burning in eastern Manitoba and western Ontario. We investigate a plume with high trace gas amounts but low amounts of particles that preceded and overlapped at the Halifax site with a second plume with high trace gas loadings and significant amounts of particulate material. We show that the first plume experienced a meteorological scavenging event but the second plume had not been similarly scavenged. This points to the necessity to account carefully for the plume history when considering long range transport since simultaneous or near-simultaneous times of arrival are not necessarily indicative of either similar trajectories or meteorological history. We investigate the origin of the scavenged plume, and the possibility of an aerosol wet deposition event occurring in the plume ~24 h prior to the measurements over Halifax. The region of lofting and scavenging is only monitored on an intermittent basis by the present observing network, and thus we must consider many different pieces of evidence in an effort to understand the early dynamics of the plume. Through this discussion we also demonstrate the value of having many simultaneous remote-sensing measurements in order to understand the physical and chemical behaviour of biomass burning plumes.

scholarly journals A case study of aerosol scavenging in a biomass burning plume over eastern Canada during the 2011 BORTAS field experiment

2014 ◽  
Vol 14 (16) ◽  
pp. 8449-8460 ◽  
Author(s):  
J. E. Franklin ◽  
J. R. Drummond ◽  
D. Griffin ◽  
J. R. Pierce ◽  
D. L. Waugh ◽  
...  
Keyword(s):  
Long Range ◽  
Biomass Burning ◽  
Forest Fires ◽  
Particulate Material ◽  
Trace Gas ◽  
Eastern Canada ◽  
Air Masses ◽  
Chemical Behaviour ◽  
Physical And Chemical ◽  
The Impact

Abstract. We present measurements of a long-range smoke transport event recorded on 20–21 July 2011 over Halifax, Nova Scotia, Canada, during the Quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS-B) campaign. Ground-based Fourier transform spectrometers and photometers detected air masses associated with large wildland fires burning in eastern Manitoba and western Ontario. We investigate a plume with high trace gas amounts but low amounts of particles that preceded and overlapped at the Halifax site with a second plume with high trace gas loadings and significant amounts of particulate material. We show that the first plume experienced a meteorological scavenging event, but the second plume had not been similarly scavenged. This points to the necessity to account carefully for the plume history when considering long-range transport since simultaneous or near-simultaneous times of arrival are not necessarily indicative of either similar trajectories or meteorological history. We investigate the origin of the scavenged plume, and the possibility of an aerosol wet deposition event occurring in the plume ~ 24 h prior to the measurements over Halifax. The region of lofting and scavenging is only monitored on an intermittent basis by the present observing network, and thus we must consider many different pieces of evidence in an effort to understand the early dynamics of the plume. Through this discussion we also demonstrate the value of having many simultaneous remote-sensing measurements in order to understand the physical and chemical behaviour of biomass burning plumes.

scholarly journals Identifying the sources driving observed PM<sub>2.5</sub> temporal variability over Halifax, Nova Scotia, during BORTAS-B

2013 ◽  
Vol 13 (14) ◽  
pp. 7199-7213 ◽  
Author(s):  
M. D. Gibson ◽  
J. R. Pierce ◽  
D. Waugh ◽  
J. S. Kuchta ◽  
L. Chisholm ◽  
...  
Keyword(s):  
Nova Scotia ◽  
Atmospheric Chemistry ◽  
Forest Fires ◽  
Atmospheric Composition ◽  
Back Trajectory ◽  
Valuable Insight ◽  
Eastern Canada ◽  
Data Set ◽  
Average Mass ◽  
The Impact

Abstract. The source attribution of observed variability of total PM2.5 concentrations over Halifax, Nova Scotia, was investigated between 11 July and 26 August 2011 using measurements of PM2.5 mass and PM2.5 chemical composition (black carbon, organic matter, anions, cations and 33 elements). This was part of the BORTAS-B (quantifying the impact of BOReal forest fires on Tropospheric oxidants using Aircraft and Satellites) experiment, which investigated the atmospheric chemistry and transport of seasonal boreal wildfire emissions over eastern Canada in 2011. The US EPA Positive Matrix Factorization (PMF) receptor model was used to determine the average mass (percentage) source contribution over the 45 days, which was estimated to be as follows: long-range transport (LRT) pollution: 1.75 μg m−3 (47%); LRT pollution marine mixture: 1.0 μg m−3 (27.9%); vehicles: 0.49 μg m−3 (13.2%); fugitive dust: 0.23 μg m−3 (6.3%); ship emissions: 0.13 μg m−3 (3.4%); and refinery: 0.081 μg m−3 (2.2%). The PMF model describes 87% of the observed variability in total PM2.5 mass (bias = 0.17 and RSME = 1.5 μg m−3). The factor identifications are based on chemical markers, and they are supported by air mass back trajectory analysis and local wind direction. Biomass burning plumes, found by other surface and aircraft measurements, were not significant enough to be identified in this analysis. This paper presents the results of the PMF receptor modelling, providing valuable insight into the local and upwind sources impacting surface PM2.5 in Halifax and a vital comparative data set for the other collocated ground-based observations of atmospheric composition made during BORTAS-B.

scholarly journals Production of peroxy nitrates in boreal biomass burning plumes over Canada during the BORTAS campaign

2016 ◽  
Vol 16 (5) ◽  
pp. 3485-3497 ◽  
Author(s):  
Marcella Busilacchio ◽  
Piero Di Carlo ◽  
Eleonora Aruffo ◽  
Fabio Biancofiore ◽  
Cesare Dari Salisburgo ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Forest Fire ◽  
Biomass Burning ◽  
Forest Fires ◽  
Chemical Mechanism ◽  
Fire Emissions ◽  
Fire Plumes ◽  
Peroxy Nitrates ◽  
In Fire ◽  
The Impact

Abstract. The observations collected during the BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS) campaign in summer 2011 over Canada are analysed to study the impact of forest fire emissions on the formation of ozone (O3) and total peroxy nitrates ∑PNs, ∑ROONO2). The suite of measurements on board the BAe-146 aircraft, deployed in this campaign, allows us to calculate the production of O3 and of  ∑PNs, a long-lived NOx reservoir whose concentration is supposed to be impacted by biomass burning emissions. In fire plumes, profiles of carbon monoxide (CO), which is a well-established tracer of pyrogenic emission, show concentration enhancements that are in strong correspondence with a significant increase of concentrations of ∑PNs, whereas minimal increase of the concentrations of O3 and NO2 is observed. The ∑PN and O3 productions have been calculated using the rate constants of the first- and second-order reactions of volatile organic compound (VOC) oxidation. The ∑PN and O3 productions have also been quantified by 0-D model simulation based on the Master Chemical Mechanism. Both methods show that in fire plumes the average production of ∑PNs and O3 are greater than in the background plumes, but the increase of ∑PN production is more pronounced than the O3 production. The average ∑PN production in fire plumes is from 7 to 12 times greater than in the background, whereas the average O3 production in fire plumes is from 2 to 5 times greater than in the background. These results suggest that, at least for boreal forest fires and for the measurements recorded during the BORTAS campaign, fire emissions impact both the oxidized NOy and O3,  but (1 ∑PN production is amplified significantly more than O3 production and (2) in the forest fire plumes the ratio between the O3 production and the ∑PN production is lower than the ratio evaluated in the background air masses, thus confirming that the role played by the ∑PNs produced during biomass burning is significant in the O3 budget. The implication of these observations is that fire emissions in some cases, for example boreal forest fires and in the conditions reported here, may influence more long-lived precursors of O3 than short-lived pollutants, which in turn can be transported and eventually diluted in a wide area.

scholarly journals Regional responses of surface ozone in Europe to the location of high-latitude blocks and subtropical ridges

2016 ◽  
Author(s):  
Carlos Ordóñez ◽  
David Barriopedro ◽  
Ricardo García-Herrera ◽  
Pedro M. Sousa ◽  
Jordan L. Schnell
Keyword(s):  
High Latitude ◽  
Climate Models ◽  
Surface Ozone ◽  
Zonal Flow ◽  
Near Surface ◽  
Air Masses ◽  
Anticyclonic Circulation ◽  
The Uk ◽  
The Impact ◽  
First Time

Abstract. This paper analyses for the first time the impact of high-latitude blocks and subtropical ridges on near-surface ozone in Europe during a 15-year period. For this purpose, a catalogue of blocks and ridges over the Euro-Atlantic region is used together with a gridded dataset of maximum daily 8-hour running average ozone (MDA8 O3) covering the period 1998–2012. The response of ozone to the location of blocks and ridges with centres in three longitudinal sectors (Atlantic, ATL, 30º–0º W; European, EUR, 0º–30º E; Russian, RUS, 30º–60º E) is examined. The impact of blocks on ozone is regionally and seasonally dependent. In particular, blocks within the EUR sector yield positive ozone anomalies of ~ 5–10 ppb over large parts of central Europe in spring and northern Europe in summer. Over 20 % and 30 % of the days with blocks in that sector register exceedances of the 90th percentile of the seasonal ozone distribution at many European locations during spring and summer, respectively. The impacts of ridges during those seasons are subtle and more sensitive to their specific location, although they can trigger ozone anomalies of ~ 5–10 ppb in Italy and the surrounding countries in summer, eventually exceeding European air quality targets. During winter, surface ozone in the northwest of Europe presents completely opposite responses to blocks and ridges. The anticyclonic circulation associated with winter EUR blocking, and to a lesser extent with ATL blocking, yields negative ozone anomalies between −5 ppb and −10 ppb over the UK, Northern France and the Benelux. Conversely, the enhanced zonal flow around 50˚–60˚ N during the occurrence of ATL ridges favours the arrival of background air masses from the Atlantic and the ventilation of the boundary layer, producing positive ozone anomalies above 5 ppb in an area spanning from the British Isles to Germany. This work provides the first quantitative assessments of the remarkable but distinct impacts that the anticyclonic circulation and the diversion of the zonal flow associated with blocks and ridges exert on surface ozone in Europe. The findings reported here can be exploited in the future to evaluate the modelled responses of ozone to circulation changes within chemical transport models (CTMs) and chemistry-climate models (CCMs).

Air mass characterization based on VOC measurements downstream of European and Asian Major Population Centers (MPC) during the research aircraft campaign EMeRGe (2017/2018)

2020 ◽  
Author(s):  
Eric Förster ◽  
Harald Bönisch ◽  
Marco Neumaier ◽  
Florian Obersteiner ◽  
Michael Lichtenstern ◽  
...  
Keyword(s):  
Mainland China ◽  
Anthropogenic Pollution ◽  
Proton Transfer Reaction ◽  
Back Trajectories ◽  
Air Masses ◽  
Airborne Measurements ◽  
Po Valley ◽  
Research Aircraft ◽  
The Impact ◽  
Pollution Plumes

&lt;p&gt;EMeRGe (Effect of Megacities on the Transport and Transformation of Pollutants on the Regional to Global Scales) aims to investigate the impact of MPC emissions on air pollution and chemical processing at local, regional and hemispheric scales by making dedicated airborne measurements using the German research aircraft HALO. Transects and vertical profiling for diverse MPCs (e.g. Rome, London, Taipei, Manila) were performed to determine the composition and transformation of various pollution plumes in Europe and Asia.&lt;/p&gt;&lt;p&gt;To characterize air masses we evaluate different volatile organic compounds (VOCs), measured by a Proton-Transfer-Reaction Mass Spectrometer (PTR-MS), with different or similar sources and different lifetimes. We use the specific tracer acetonitrile to identify air masses influenced by biomass burning (BB), the aromatic compound benzene to tag anthropogenic pollution plumes (e.g. from traffic or industry) and short-lived isoprene as indicator for fresh biogenic influences. Back trajectories based on FLEXTRA (FLEXible TRAjectory model) are used to determine potential source regions of BB affected air and anthropogenic pollution plumes.&lt;/p&gt;&lt;p&gt;Results show that in Europe only minor BB influenced air masses were sampled. However, in Southern France fresh BB close to the source was detected. In contrast to Europe, numerous plumes affected by BB were identified in Asia originating mostly from Southeast Asia.&lt;/p&gt;&lt;p&gt;Air masses with enhanced concentrations in benzene and low concentrations in acetonitrile, indicating anthropogenic pollution, were sampled in Europe over the Po-Valley, Rome, Barcelona and the English Channel. In Asia, plumes were identified along the west coast of Taiwan, the East China Sea and Manila originating from local sources as well as transported from Mainland China.&lt;/p&gt;&lt;p&gt;Significant fresh biogenic influence was found in Europe, as the measurements were performed mostly in summer over land in contrast to Asia were just a minor influence was detected.&lt;/p&gt;

scholarly journals Identifying the sources driving observed PM<sub>2.5</sub> variability over Halifax, Nova Scotia, during BORTAS-B

2013 ◽  
Vol 13 (2) ◽  
pp. 4491-4533 ◽  
Author(s):  
M. D. Gibson ◽  
J. R. Pierce ◽  
D. Waugh ◽  
J. S. Kuchta ◽  
L. Chisholm ◽  
...  
Keyword(s):  
Nova Scotia ◽  
Atmospheric Chemistry ◽  
Forest Fires ◽  
Back Trajectory ◽  
Valuable Insight ◽  
Eastern Canada ◽  
Average Mass ◽  
Fire Emissions ◽  
Pmf Model ◽  
The Impact

Abstract. The source attribution of observed variability of total PM2.5 concentrations over Halifax, Nova Scotia was investigated between 11 July–26 August 2011 using measurements of PM2.5 mass and PM2.5 chemical composition (black carbon, organic matter, anions, cations and 33 elements). This was part of the BORTAS-B (quantifying the impact of BOReal forest fires on Tropospheric oxidants using aircraft and satellites) experiment, which investigated the atmospheric chemistry and transport of seasonal boreal wild fire emissions over eastern Canada in 2011. The US EPA Positive Matrix Factorization (PMF) receptor model was used to determine the average mass (percentage) source contribution over the 45 days, which was estimated to be: Long-Range Transport (LRT) Pollution 1.75 μg m−3 (47%), LRT Pollution Marine Mixture 1.0 μg m−3 (27.9%), Vehicles 0.49 μg m−3 (13.2%), Fugitive Dust 0.23 μg m−3 (6.3%), Ship Emissions 0.13 μg m−3 (3.4%) and Refinery 0.081 μg m−3 (2.2%). The PMF model describes 87% of the observed variability in total PM2.5 mass (bias = 0.17 and RSME = 1.5 μg m−3). The factor identifications are based on chemical markers, and they are supported by air mass back trajectory analysis and local wind direction. Biomass burning plumes, found by other surface and aircraft measurements, were not significant enough to be identified in this analysis. This paper presents the results of the PMF receptor modelling, providing valuable insight into the local and upwind sources impacting surface PM2.5 in Halifax during the BORTAS-B mission.

scholarly journals Megacity and local contributions to regional air pollution: An aircraft case study over London

2019 ◽  
Author(s):  
Kirsti Ashworth ◽  
Silvia Bucci ◽  
Peter J. Gallimore ◽  
Junghwa Lee ◽  
Beth S. Nelson ◽  
...  
Keyword(s):  
Air Quality ◽  
Early Career ◽  
Atmospheric Measurements ◽  
Airborne Measurements ◽  
Sources Of Pollution ◽  
Pollutant Concentrations ◽  
Local Sources ◽  
The Uk ◽  
The Impact ◽  
Pollution Events

Abstract. In July 2017 three research flights circumnavigating the megacity of London were conducted as a part of the STANCO training school for students and early career researchers organised by EUFAR (European Facility for Aircraft Research). Measurements were made from the UK’s Facility for Airborne Atmospheric Measurements (FAAM) BAe-146-301 Atmospheric Research Aircraft with the aim to sample, characterise and quantify the impact of megacity outflow pollution on air quality in the surrounding region. Conditions were extremely favourable for airborne measurements and all three flights were able to observe clear pollution events along the flight path. A small change in wind direction provided sufficiently different airmass origins over the two days such that a distinct pollution plume from London, attributable marine emissions and a double-peaked dispersed area of pollution resulting from a combination of local and transported emissions were measured. We were able to analyse the effect of London emissions on air quality in the wider region and the extent to which local sources contribute to pollution events. The background air upwind of London was relatively clean during both days; concentrations of CO were 88–95 ppbv, total (measured) volatile organic compounds (VOCs) were 1.6–1.8 ppbv, and NOx were 0.7–0.8 ppbv. Downwind of London, we encountered elevations in all species with CO > 100 ppbv, VOCs 2.8–3.8 ppbv, CH4 > 2080 ppbv and NOx > 4 ppbv, and peak concentrations in individual pollution events higher still. Levels of O3 were inversely correlated with NOx during the first flight, with O3 concentrations of 37 ppbv upwind falling to ~ 26 ppbv in the well-defined London plume. Mass balance techniques were applied to estimate pollutant fluxes from London. Our calculated CO2 fluxes are within 10 % of those estimated previously, but there was a greater disparity in our estimates of CH4 and CO. On the second day, winds were lighter and downwind O3 concentrations were elevated to ~ 39–43 ppbv (from ~ 32–35 ppbv upwind), reflecting the contribution of more aged pollution to the regional background. Elevations in pollutant concentrations were dispersed over a wider area than the first day, although we also encountered a number of clear spikes from local sources. This series of flights demonstrated that megacity outflow, local fresh emissions and more distant UK sources of pollution all contribute to pollution events in the southeast of the UK. These sources must therefore all be well-characterised and constrained to understand air quality around London.

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