Comment on acp-2021-500

EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales) is an international project focusing on atmospheric chemistry, dynamics and transport of local and regional pollution originating in megacities and other major population centres (MPCs). Airborne measurements, taking advantage of the long range capabilities of the HALO research platform (High Altitude and Long range research aircraft, www.halo-spp.de), are a central part of the research project. In order to provide an adequate set of measurements at different spatial scales, two field experiments were positioned in time and space to contrast situations when the photochemical transformation of plumes emerging from MPCs is large. These experiments were conducted in summer 2017 over Europe and in the inter-monsoon period over Asia in spring 2018. The intensive observational periods (IOP) involved HALO airborne measurements of ozone and its precursors, volatile organic compounds, aerosol particles and related species as well as coordinated ground-based ancillary observations at different sites. Perfluorocarbon (PFC) tracer releases and model forecasts supported the flight planning and the identification of pollution plumes. This paper describes the experimental deployment of the IOP in Europe, which comprised 7 HALO research flights with aircraft base in Oberpfaffenhofen (Germany) for a total of 53 flight hours. The MPC targets London (Great Britain), Benelux/Ruhr area (Belgium, The Netherlands, Luxembourg and Germany), Paris (France), Rome and Po Valley (Italy), Madrid and Barcelona (Spain) were investigated. An in-flight comparison of HALO with the collaborating UK-airborne platform FAAM took place to assure accuracy and comparability of the instrumentation on-board. Generally, significant enhancement of trace gases and aerosol particles are attributed to emissions originating in MPCs at distances of hundreds of kilometres from the sources. The proximity of different MPCs over Europe favours the mixing of plumes of different origin and level of processing and hampers the unambiguous attribution of the MPC sources. Similarly, urban plumes mix efficiently with natural sources as desert dust and with biomass burning emissions from vegetation and forest fires. This confirms the importance of wildland fire emissions in Europe and indicates an important but discontinuous contribution to the European emission budget that might be of relevance in the design of efficient mitigation strategies. The synergistic use and consistent interpretation of observational data sets of different spatial and temporal resolution (e.g. from ground-based networks, airborne campaigns, and satellite measurements) supported by modelling within EMeRGe, provides a unique insight to test the current understanding of MPC pollution outflows. The present work provides an overview of the most salient results and scientific questions in the European context, these being addressed in more detail within additional dedicated EMeRGe studies. The deployment and results obtained in Asia will be the subject of separate publications.

EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales) is an international project focusing on atmospheric chemistry, dynamics and transport of local and regional pollution originating in megacities and other major population centres (MPCs). Airborne measurements, taking advantage of the long range capabilities of the HALO research platform (High Altitude and Long range research aircraft, www.halo-spp.de), are a central part of the research project. In order to provide an adequate set of measurements at different spatial scales, two field experiments were positioned in time and space to contrast situations when the photochemical transformation of plumes emerging from MPCs is large. These experiments were conducted in summer 2017 over Europe and in the inter-monsoon period over Asia in spring 2018. The intensive observational periods (IOP) involved HALO airborne measurements of ozone and its precursors, volatile organic compounds, aerosol particles and related species as well as coordinated ground-based ancillary observations at different sites. Perfluorocarbon (PFC) tracer releases and model forecasts supported the flight planning and the identification of pollution plumes. This paper describes the experimental deployment of the IOP in Europe, which comprised 7 HALO research flights with aircraft base in Oberpfaffenhofen (Germany) for a total of 53 flight hours. The MPC targets London (Great Britain), Benelux/Ruhr area (Belgium, The Netherlands, Luxembourg and Germany), Paris (France), Rome and Po Valley (Italy), Madrid and Barcelona (Spain) were investigated. An in-flight comparison of HALO with the collaborating UK-airborne platform FAAM took place to assure accuracy and comparability of the instrumentation on-board. Generally, significant enhancement of trace gases and aerosol particles are attributed to emissions originating in MPCs at distances of hundreds of kilometres from the sources. The proximity of different MPCs over Europe favours the mixing of plumes of different origin and level of processing and hampers the unambiguous attribution of the MPC sources. Similarly, urban plumes mix efficiently with natural sources as desert dust and with biomass burning emissions from vegetation and forest fires. This confirms the importance of wildland fire emissions in Europe and indicates an important but discontinuous contribution to the European emission budget that might be of relevance in the design of efficient mitigation strategies. The synergistic use and consistent interpretation of observational data sets of different spatial and temporal resolution (e.g. from ground-based networks, airborne campaigns, and satellite measurements) supported by modelling within EMeRGe, provides a unique insight to test the current understanding of MPC pollution outflows. The present work provides an overview of the most salient results and scientific questions in the European context, these being addressed in more detail within additional dedicated EMeRGe studies. The deployment and results obtained in Asia will be the subject of separate publications.

EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales) is an international project focusing on atmospheric chemistry, dynamics and transport of local and regional pollution originating in megacities and other major population centres (MPCs). Airborne measurements, taking advantage of the long range capabilities of the HALO research platform (High Altitude and Long range research aircraft, www.halo-spp.de), are a central part of the research project. In order to provide an adequate set of measurements at different spatial scales, two field experiments were positioned in time and space to contrast situations when the photochemical transformation of plumes emerging from MPCs is large. These experiments were conducted in summer 2017 over Europe and in the inter-monsoon period over Asia in spring 2018. The intensive observational periods (IOP) involved HALO airborne measurements of ozone and its precursors, volatile organic compounds, aerosol particles and related species as well as coordinated ground-based ancillary observations at different sites. Perfluorocarbon (PFC) tracer releases and model forecasts supported the flight planning and the identification of pollution plumes. This paper describes the experimental deployment of the IOP in Europe, which comprised 7 HALO research flights with aircraft base in Oberpfaffenhofen (Germany) for a total of 53 flight hours. The MPC targets London (Great Britain), Benelux/Ruhr area (Belgium, The Netherlands, Luxembourg and Germany), Paris (France), Rome and Po Valley (Italy), Madrid and Barcelona (Spain) were investigated. An in-flight comparison of HALO with the collaborating UK-airborne platform FAAM took place to assure accuracy and comparability of the instrumentation on-board. Generally, significant enhancement of trace gases and aerosol particles are attributed to emissions originating in MPCs at distances of hundreds of kilometres from the sources. The proximity of different MPCs over Europe favours the mixing of plumes of different origin and level of processing and hampers the unambiguous attribution of the MPC sources. Similarly, urban plumes mix efficiently with natural sources as desert dust and with biomass burning emissions from vegetation and forest fires. This confirms the importance of wildland fire emissions in Europe and indicates an important but discontinuous contribution to the European emission budget that might be of relevance in the design of efficient mitigation strategies. The synergistic use and consistent interpretation of observational data sets of different spatial and temporal resolution (e.g. from ground-based networks, airborne campaigns, and satellite measurements) supported by modelling within EMeRGe, provides a unique insight to test the current understanding of MPC pollution outflows. The present work provides an overview of the most salient results and scientific questions in the European context, these being addressed in more detail within additional dedicated EMeRGe studies. The deployment and results obtained in Asia will be the subject of separate publications.

Abstract. Megacities and other major population centres (MPCs) worldwide are major sources of air pollution, both locally as well as downwind. The overall assessment and prediction of the impact of MPC pollution on tropospheric chemistry are challenging. The present work provides an overview of the highlights of a major new contribution to the understanding of this issue based on the data and analysis of the EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales) international project. EMeRGe focuses on atmospheric chemistry, dynamics, and transport of local and regional pollution originating in MPCs. Airborne measurements, taking advantage of the long range capabilities of the High Altitude and LOng Range Research Aircraft (HALO, https://www.halo-spp.de, last access: 22 March 2022), are a central part of the project. The synergistic use and consistent interpretation of observational data sets of different spatial and temporal resolution (e.g. from ground-based networks, airborne campaigns, and satellite measurements) supported by modelling within EMeRGe provide unique insight to test the current understanding of MPC pollution outflows. In order to obtain an adequate set of measurements at different spatial scales, two field experiments were positioned in time and space to contrast situations when the photochemical transformation of plumes emerging from MPCs is large. These experiments were conducted in summer 2017 over Europe and in the inter-monsoon period over Asia in spring 2018. The intensive observational periods (IOPs) involved HALO airborne measurements of ozone and its precursors, volatile organic compounds, aerosol particles, and related species as well as coordinated ground-based ancillary observations at different sites. Perfluorocarbon (PFC) tracer releases and model forecasts supported the flight planning, the identification of pollution plumes, and the analysis of chemical transformations during transport. This paper describes the experimental deployment and scientific questions of the IOP in Europe. The MPC targets – London (United Kingdom; UK), the Benelux/Ruhr area (Belgium, the Netherlands, Luxembourg and Germany), Paris (France), Rome and the Po Valley (Italy), and Madrid and Barcelona (Spain) – were investigated during seven HALO research flights with an aircraft base in Germany for a total of 53 flight hours. An in-flight comparison of HALO with the collaborating UK-airborne platform Facility for Airborne Atmospheric Measurements (FAAM) took place to assure accuracy and comparability of the instrumentation on board. Overall, EMeRGe unites measurements of near- and far-field emissions and hence deals with complex air masses of local and distant sources. Regional transport of several European MPC outflows was successfully identified and measured. Chemical processing of the MPC emissions was inferred from airborne observations of primary and secondary pollutants and the ratios between species having different chemical lifetimes. Photochemical processing of aerosol and secondary formation or organic acids was evident during the transport of MPC plumes. Urban plumes mix efficiently with natural sources as mineral dust and with biomass burning emissions from vegetation and forest fires. This confirms the importance of wildland fire emissions in Europe and indicates an important but discontinuous contribution to the European emission budget that might be of relevance in the design of efficient mitigation strategies. The present work provides an overview of the most salient results in the European context, with these being addressed in more detail within additional dedicated EMeRGe studies. The deployment and results obtained in Asia will be the subject of separate publications.

<strong class="journal-contentHeaderColor">Abstract.</strong> In this study, airborne measurements of the sum of hydroperoxyl (HO₂) and organic peroxy (RO₂) radicals that react with NO to produce NO₂, i.e. RO₂^*, coupled with actinometry and other key trace gases measurements, have been used to test the current understanding of the fast photochemistry in the outflow of major population centres (MPCs). All measurements were made during the airborne campaign of the EMeRGe (<strong>E</strong>ffect of <strong>M</strong>egacities on the transport and transformation of pollutants on the <strong>R</strong>egional to <strong>G</strong>lobal scal<strong>e</strong>s) project in Europe on-board the <strong>H</strong>igh <strong>A</strong>ltitude <strong>Lo</strong>ng range research aircraft (HALO). The on-board measurements of RO₂^* were made using the in-situ instrument <strong>P</strong>eroxy <strong>R</strong>adical <strong>C</strong>hemical <strong>E</strong>nhancement and <strong>A</strong>bsorption <strong>S</strong>pectrometer (PeRCEAS). RO₂^* mixing ratios up to 120 pptv were observed in air masses of different origins and composition under different local actinometrical conditions during seven HALO research flights in July 2017 over Europe. The range and variability of the RO₂^* measurements agree reasonably well with radical production rates estimated using photolysis frequencies and RO₂^* precursor concentrations measured on-board. RO₂^* is primarily produced following the photolysis of ozone (O₃), formaldehyde (HCHO), glyoxal (CHOCHO), and nitrous acid (HONO) in the airmasses investigated. The suitability of <strong>p</strong>hotostationary <strong>s</strong>teady-<strong>s</strong>tate (PSS) assumptions to estimate the mixing ratios and the variability of RO₂^* during the airborne observations is investigated. The PSS assumption is robust enough to calculate RO₂^* mixing rations for most conditions encountered in air masses measured. The similarities and discrepancies between measured and calculated RO₂^* mixing ratios are analysed stepwise. The parameters, which predominantly control the RO₂^* mixing ratios under different chemical and physical regimes, are identified during the analysis. The dominant removal processes of RO₂^* in the airmasses measured up to 2000 m are the loss of OH and RO through the reaction with NO_x during the radical interconversion. Above 2000 m, HO₂ &ndash; HO₂ and HO₂ &ndash; RO₂ reactions dominate RO₂^* loss reactions. RO₂^* calculations underestimated (&lt; 20 %) the measurements by the analytical expression inside the pollution plumes probed. The underestimation is attributed to the limitations of the PSS analysis to take into account the production of RO₂^* through oxidation and photolysis of the OVOCs not measured during EMeRGe.

In this study, airborne measurements of the sum of hydroperoxyl (HO2) and organic peroxy (RO2) radicals that react with NO to produce NO2, i.e. RO2*, coupled with actinometry and other key trace gases measurements, have been used to test the current understanding of the fast photochemistry in the outflow of major population centres (MPCs). All measurements were made during the airborne campaign of the EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales) project in Europe on-board the High Altitude Long range research aircraft (HALO). The on-board measurements of RO2* were made using the in-situ instrument Peroxy Radical Chemical Enhancement and Absorption Spectrometer (PeRCEAS). RO2* mixing ratios up to 120 pptv were observed in air masses of different origins and composition under different local actinometrical conditions during seven HALO research flights in July 2017 over Europe. The range and variability of the RO2* measurements agree reasonably well with radical production rates estimated using photolysis frequencies and RO2* precursor concentrations measured on-board. RO2* is primarily produced following the photolysis of ozone (O3), formaldehyde (HCHO), glyoxal (CHOCHO), and nitrous acid (HONO) in the airmasses investigated. The suitability of photostationary steady-state (PSS) assumptions to estimate the mixing ratios and the variability of RO2* during the airborne observations is investigated. The PSS assumption is robust enough to calculate RO2* mixing rations for most conditions encountered in air masses measured. The similarities and discrepancies between measured and calculated RO2* mixing ratios are analysed stepwise. The parameters, which predominantly control the RO2* mixing ratios under different chemical and physical regimes, are identified during the analysis. The dominant removal processes of RO2* in the airmasses measured up to 2000 m are the loss of OH and RO through the reaction with NOx during the radical interconversion. Above 2000 m, HO2 – HO2 and HO2 – RO2 reactions dominate RO2* loss reactions. RO2* calculations underestimated (< 20 %) the measurements by the analytical expression inside the pollution plumes probed. The underestimation is attributed to the limitations of the PSS analysis to take into account the production of RO2* through oxidation and photolysis of the OVOCs not measured during EMeRGe.

In this study, airborne measurements of the sum of hydroperoxyl (HO2) and organic peroxy (RO2) radicals that react with NO to produce NO2, i.e. RO2*, coupled with actinometry and other key trace gases measurements, have been used to test the current understanding of the fast photochemistry in the outflow of major population centres (MPCs). All measurements were made during the airborne campaign of the EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales) project in Europe on-board the High Altitude Long range research aircraft (HALO). The on-board measurements of RO2* were made using the in-situ instrument Peroxy Radical Chemical Enhancement and Absorption Spectrometer (PeRCEAS). RO2* mixing ratios up to 120 pptv were observed in air masses of different origins and composition under different local actinometrical conditions during seven HALO research flights in July 2017 over Europe. The range and variability of the RO2* measurements agree reasonably well with radical production rates estimated using photolysis frequencies and RO2* precursor concentrations measured on-board. RO2* is primarily produced following the photolysis of ozone (O3), formaldehyde (HCHO), glyoxal (CHOCHO), and nitrous acid (HONO) in the airmasses investigated. The suitability of photostationary steady-state (PSS) assumptions to estimate the mixing ratios and the variability of RO2* during the airborne observations is investigated. The PSS assumption is robust enough to calculate RO2* mixing rations for most conditions encountered in air masses measured. The similarities and discrepancies between measured and calculated RO2* mixing ratios are analysed stepwise. The parameters, which predominantly control the RO2* mixing ratios under different chemical and physical regimes, are identified during the analysis. The dominant removal processes of RO2* in the airmasses measured up to 2000 m are the loss of OH and RO through the reaction with NOx during the radical interconversion. Above 2000 m, HO2 – HO2 and HO2 – RO2 reactions dominate RO2* loss reactions. RO2* calculations underestimated (< 20 %) the measurements by the analytical expression inside the pollution plumes probed. The underestimation is attributed to the limitations of the PSS analysis to take into account the production of RO2* through oxidation and photolysis of the OVOCs not measured during EMeRGe.

In this study, airborne measurements of the sum of hydroperoxyl (HO2) and organic peroxy (RO2) radicals that react with NO to produce NO2, i.e. RO2*, coupled with actinometry and other key trace gases measurements, have been used to test the current understanding of the fast photochemistry in the outflow of major population centres (MPCs). All measurements were made during the airborne campaign of the EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales) project in Europe on-board the High Altitude Long range research aircraft (HALO). The on-board measurements of RO2* were made using the in-situ instrument Peroxy Radical Chemical Enhancement and Absorption Spectrometer (PeRCEAS). RO2* mixing ratios up to 120 pptv were observed in air masses of different origins and composition under different local actinometrical conditions during seven HALO research flights in July 2017 over Europe. The range and variability of the RO2* measurements agree reasonably well with radical production rates estimated using photolysis frequencies and RO2* precursor concentrations measured on-board. RO2* is primarily produced following the photolysis of ozone (O3), formaldehyde (HCHO), glyoxal (CHOCHO), and nitrous acid (HONO) in the airmasses investigated. The suitability of photostationary steady-state (PSS) assumptions to estimate the mixing ratios and the variability of RO2* during the airborne observations is investigated. The PSS assumption is robust enough to calculate RO2* mixing rations for most conditions encountered in air masses measured. The similarities and discrepancies between measured and calculated RO2* mixing ratios are analysed stepwise. The parameters, which predominantly control the RO2* mixing ratios under different chemical and physical regimes, are identified during the analysis. The dominant removal processes of RO2* in the airmasses measured up to 2000 m are the loss of OH and RO through the reaction with NOx during the radical interconversion. Above 2000 m, HO2 – HO2 and HO2 – RO2 reactions dominate RO2* loss reactions. RO2* calculations underestimated (< 20 %) the measurements by the analytical expression inside the pollution plumes probed. The underestimation is attributed to the limitations of the PSS analysis to take into account the production of RO2* through oxidation and photolysis of the OVOCs not measured during EMeRGe.

&amp;lt;p&amp;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.&amp;lt;/p&amp;gt;&amp;lt;p&amp;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.&amp;lt;/p&amp;gt;&amp;lt;p&amp;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.&amp;lt;/p&amp;gt;&amp;lt;p&amp;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.&amp;lt;/p&amp;gt;&amp;lt;p&amp;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.&amp;lt;/p&amp;gt;

&amp;lt;p&amp;gt;Today, the majority of humanity lives in urban areas. Accordingly, major population centers are a significant source of a multitude of atmospheric emissions from human activity such as traffic, heating, industry or power generation. Pollutants directly impact the local inhabitant's health, but are also transported to neighbouring areas, undergo chemical evolution and can have an impact on climate. To understand and assess effective measures for reducing the effects, it is important to determine the source locations and strengths as well as relevant chemical processes.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Aircraft-based measurements can cover the gap between long-term ground-based and globe-covering satellite instruments with its high temporal and spatial coverage during flight time. Remote sensing methods in particular allow a fast and wide-spread probing of atmospheric trace gas distributions. Within this context, the HAIDI (Heidelberg Airborne Imaging DOAS Instrument) instrument was designed to provide data of extremely high temporal and spatial resolution (40m x 40m at 1.5 km flight altitude, 266m x 266m at 10 km flight altitude, at 10 ms temporal resolution) in 2D and 3D during overflight.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;During the EMeRGe (Effect of Megacities on the Transport and Transformation of Pollutants on the Regional to Global Scales) missions HAIDI was part of the comprehensive set of measurement equipment installed on the research airplane HALO (High Altitude and LOng range re-search aircraft) of the DLR (German Aerospace Center). The EMeRGe missions targeted the emission outflows of megacities to investigate their compositions and the atmospheric impact of urban pollution. One mission part was conducted in Europe (July 2017) and aimed at areas around Paris, London, the Po area, Madrid and the Benelux area. For contrast, the second mission part was based in Taiwan (March 2018) and investigated Taiwan cities, Bangkok, Manila, Japanese cities and China outflow.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;HAIDI derived a number of trace gases such as NO2, SO2, BrO and HCHO. Due to large concentrations present, for NO2 and SO2 in particular it was possible to obtain high-resolution 2D data of megacity areas and plumes of megacities, powerplants and ships and estimate their emissions. We will present results of the HAIDI measurements during the EMeRGe mission.&amp;lt;/p&amp;gt;

Worldwide the number of large urban agglomerations is steadily increasing. At a local scale, their emissions lead to air pollution, directly affecting people’s health. On a global scale, their emissions lead to an increase of greenhouse gases, affecting climate. In this context, in 2017 and 2018, the airborne campaigns EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales) investigated emissions of European and Asian major population centres (MPCs) to improve the understanding and predictability of pollution outflows. Here, we present two methods to identify and characterise emission outflows probed during EMeRGe. First, we use a set of volatile organic compounds (VOCs) as chemical tracers to characterise air-masses by specific source signals, i.e. benzene from anthropogenic emissions of targeted regions, acetonitrile from biomass burning (BB, primarily during EMeRGe-Asia) and isoprene from fresh biogenic signals (primarily during EMeRGe-Europe). Second, we attribute probed air-masses to source regions and estimate their individual contribution by constructing and applying a simple emission uptake scheme for the boundary layer which combines FLEXTRA back-trajectories and EDGAR carbon monoxide (CO) emission rates (acronyms are provided in Appendix A). During EMeRGe-Europe, we identified anthropogenic emission outflows from Northern Italy, Southern Great Britain, the Belgium-Netherlands-Ruhr area and the Iberian Peninsula. Additionally, our uptake scheme indicates significant long-range transport of emissions from the USA and Canada. During EMeRGe-Asia, the emission outflow is dominated by sources in China and Taiwan, with further emissions (mostly from BB) originating from Southeast Asia and India. Emissions of pre-selected MPC targets are identified in less than 20 % of the sampling time, due to restrictions in flight planning and constraints of the measurement platform itself. Still, EMeRGe combines in a unique way near- and far-field measurements, which show signatures of local and distant sources, transport and conversion fingerprints and complex emission mixtures. Our approach already provides a valuable classification and characterisation of the EMeRGe dataset, e.g. for BB and anthropogenic influence of potential source regions, and paves the way for a more comprehensive analysis and various model studies.

Worldwide the number of large urban agglomerations is steadily increasing. At a local scale, their emissions lead to air pollution, directly affecting people’s health. On a global scale, their emissions lead to an increase of greenhouse gases, affecting climate. In this context, in 2017 and 2018, the airborne campaigns EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales) investigated emissions of European and Asian major population centres (MPCs) to improve the understanding and predictability of pollution outflows. Here, we present two methods to identify and characterise emission outflows probed during EMeRGe. First, we use a set of volatile organic compounds (VOCs) as chemical tracers to characterise air-masses by specific source signals, i.e. benzene from anthropogenic emissions of targeted regions, acetonitrile from biomass burning (BB, primarily during EMeRGe-Asia) and isoprene from fresh biogenic signals (primarily during EMeRGe-Europe). Second, we attribute probed air-masses to source regions and estimate their individual contribution by constructing and applying a simple emission uptake scheme for the boundary layer which combines FLEXTRA back-trajectories and EDGAR carbon monoxide (CO) emission rates (acronyms are provided in Appendix A). During EMeRGe-Europe, we identified anthropogenic emission outflows from Northern Italy, Southern Great Britain, the Belgium-Netherlands-Ruhr area and the Iberian Peninsula. Additionally, our uptake scheme indicates significant long-range transport of emissions from the USA and Canada. During EMeRGe-Asia, the emission outflow is dominated by sources in China and Taiwan, with further emissions (mostly from BB) originating from Southeast Asia and India. Emissions of pre-selected MPC targets are identified in less than 20 % of the sampling time, due to restrictions in flight planning and constraints of the measurement platform itself. Still, EMeRGe combines in a unique way near- and far-field measurements, which show signatures of local and distant sources, transport and conversion fingerprints and complex emission mixtures. Our approach already provides a valuable classification and characterisation of the EMeRGe dataset, e.g. for BB and anthropogenic influence of potential source regions, and paves the way for a more comprehensive analysis and various model studies.

<strong class="journal-contentHeaderColor">Abstract.</strong> Worldwide the number of large urban agglomerations is steadily increasing. At a local scale, their emissions lead to air pollution, directly affecting people&rsquo;s health. On a global scale, their emissions lead to an increase of greenhouse gases, affecting climate. In this context, in 2017 and 2018, the airborne campaigns EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales) investigated emissions of European and Asian major population centres (MPCs) to improve the understanding and predictability of pollution outflows. Here, we present two methods to identify and characterise emission outflows probed during EMeRGe. First, we use a set of volatile organic compounds (VOCs) as chemical tracers to characterise air-masses by specific source signals, i.e. benzene from anthropogenic emissions of targeted regions, acetonitrile from biomass burning (BB, primarily during EMeRGe-Asia) and isoprene from fresh biogenic signals (primarily during EMeRGe-Europe). Second, we attribute probed air-masses to source regions and estimate their individual contribution by constructing and applying a simple emission uptake scheme for the boundary layer which combines FLEXTRA back-trajectories and EDGAR carbon monoxide (CO) emission rates (acronyms are provided in Appendix A). During EMeRGe-Europe, we identified anthropogenic emission outflows from Northern Italy, Southern Great Britain, the Belgium-Netherlands-Ruhr area and the Iberian Peninsula. Additionally, our uptake scheme indicates significant long-range transport of emissions from the USA and Canada. During EMeRGe-Asia, the emission outflow is dominated by sources in China and Taiwan, with further emissions (mostly from BB) originating from Southeast Asia and India. Emissions of pre-selected MPC targets are identified in less than 20 % of the sampling time, due to restrictions in flight planning and constraints of the measurement platform itself. Still, EMeRGe combines in a unique way near- and far-field measurements, which show signatures of local and distant sources, transport and conversion fingerprints and complex emission mixtures. Our approach already provides a valuable classification and characterisation of the EMeRGe dataset, e.g. for BB and anthropogenic influence of potential source regions, and paves the way for a more comprehensive analysis and various model studies.

Worldwide the number of large urban agglomerations is steadily increasing. At a local scale, their emissions lead to air pollution, directly affecting people’s health. On a global scale, their emissions lead to an increase of greenhouse gases, affecting climate. In this context, in 2017 and 2018, the airborne campaigns EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales) investigated emissions of European and Asian major population centres (MPCs) to improve the understanding and predictability of pollution outflows. Here, we present two methods to identify and characterise emission outflows probed during EMeRGe. First, we use a set of volatile organic compounds (VOCs) as chemical tracers to characterise air-masses by specific source signals, i.e. benzene from anthropogenic emissions of targeted regions, acetonitrile from biomass burning (BB, primarily during EMeRGe-Asia) and isoprene from fresh biogenic signals (primarily during EMeRGe-Europe). Second, we attribute probed air-masses to source regions and estimate their individual contribution by constructing and applying a simple emission uptake scheme for the boundary layer which combines FLEXTRA back-trajectories and EDGAR carbon monoxide (CO) emission rates (acronyms are provided in Appendix A). During EMeRGe-Europe, we identified anthropogenic emission outflows from Northern Italy, Southern Great Britain, the Belgium-Netherlands-Ruhr area and the Iberian Peninsula. Additionally, our uptake scheme indicates significant long-range transport of emissions from the USA and Canada. During EMeRGe-Asia, the emission outflow is dominated by sources in China and Taiwan, with further emissions (mostly from BB) originating from Southeast Asia and India. Emissions of pre-selected MPC targets are identified in less than 20 % of the sampling time, due to restrictions in flight planning and constraints of the measurement platform itself. Still, EMeRGe combines in a unique way near- and far-field measurements, which show signatures of local and distant sources, transport and conversion fingerprints and complex emission mixtures. Our approach already provides a valuable classification and characterisation of the EMeRGe dataset, e.g. for BB and anthropogenic influence of potential source regions, and paves the way for a more comprehensive analysis and various model studies.

Abstract. The number of large urban agglomerations is steadily increasing worldwide. At a local scale, their emissions lead to air pollution, directly affecting people's health. On a global scale, their emissions lead to an increase of greenhouse gases, affecting climate. In this context, in 2017 and 2018, the airborne campaign EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales) investigated emissions of European and Asian major population centres (MPCs) to improve the understanding and predictability of pollution outflows. Here, we present two methods to identify and characterise pollution outflows probed during EMeRGe. First, we use a set of volatile organic compounds (VOCs) as chemical tracers to characterise air masses by specific source signals, i.e. benzene from anthropogenic pollution of targeted regions, acetonitrile from biomass burning (BB, primarily during EMeRGe-Asia), and isoprene from fresh biogenic signals (primarily during EMeRGe-Europe. Second, we attribute probed air masses to source regions and estimate their individual contribution by constructing and applying a simple emission uptake scheme for the boundary layer which combines FLEXTRA back trajectories and EDGAR carbon monoxide (CO) emission rates (acronyms are provided in the Appendix). During EMeRGe-Europe, we identified anthropogenic pollution outflows from northern Italy, southern Great Britain, the Belgium–Netherlands–Ruhr (BNR) area and the Iberian Peninsula. Additionally, our uptake scheme indicates significant long-range transport of pollution from the USA and Canada. During EMeRGe-Asia, the pollution outflow is dominated by sources in China and Taiwan, but BB signals from Southeast Asia and India contribute as well. Outflows of pre-selected MPC targets are identified in less than 20 % of the sampling time, due to restrictions in flight planning and constraints of the measurement platform itself. Still, EMeRGe combines in a unique way near- and far-field measurements, which show signatures of local and distant sources, transport and conversion fingerprints, and complex air mass compositions. Our approach provides a valuable classification and characterisation of the EMeRGe dataset, e.g. for BB and anthropogenic influence of potential source regions and paves the way for a more comprehensive analysis and various model studies.