Airborne measurements of trace gases and aerosols over the London metropolitan region

Abstract

Abstract. The Emissions around the M25 motorway (EM25) campaign took place over the megacity of London in the United Kingdom in June 2009 with the aim of characterising trace gas and aerosol composition and properties entering and emitted from the urban region. It featured two mobile platforms, the UK BAe-146 Facility for Airborne Atmospheric Measurements (FAAM) research aircraft and a ground-based mobile lidar van, both travelling in circuits around London, roughly following the path of the M25 motorway circling the city. We present an overview of findings from the project, which took place during typical UK summertime pollution conditions. Emission ratios of volatile organic compounds (VOCs) to acetylene and carbon monoxide emitted from the London region were consistent with measurements in and downwind of other large urban areas and indicated traffic and associated fuel evaporation were major sources. Sub-micron aerosol composition was dominated by secondary species including sulphate (24 % of sub-micron mass in the London plume and 29 % in the non-plume regional aerosol), nitrate (24 % plume; 20 % regional) and organic aerosol (29 % plume; 31 % regional). The primary submicron aerosol emissions from London were minor compared to the larger regional background, with only limited increases in aerosol mass in the urban plume compared to the background (∼12 % mass increase on average). Black carbon mass was the major exception and more than doubled in the urban plume, leading to a decrease in the single scattering albedo from 0.91 in the regional aerosol to 0.86 in the London plume, on average. Our observations indicated that regional aerosol plays a major role on aerosol concentrations around London, at least during typical summertime conditions, meaning future efforts to reduce PM levels in London must account for regional as well as local aerosol sources.

AERONET-based models of smoke-dominated aerosol near source regions and transported over oceans, and implications for satellite retrievals of aerosol optical depth

“…This is consistent with the idea that biomass burning aerosols show weaker hygroscopicity than other fine-dominated aerosols (e.g. Reid et al, 2005a;McMeeking et al, 2012), and that ageing processes may have occurred rapidly and prior to the aerosols reaching the AERONET site. This could also be linked to the small gradient of the observed τ f,550 -r v,f relationships at these sites, which are up to about an order of magnitude weaker than observed for more hygroscopic urban/industrial aerosol particles (e.g.…”

“…Eck et al, 1999;Dubovik et al, 2002;Salinas et al, 2009;Bovchaliuk et al, 2013) or other techniques (e.g. He et al, 2009;Gyawali et al, 2012;McMeeking et al, 2012). On the one hand this means that optical models based on smoke may also be appropriate optical proxies for mixed smoke/urban or urban aerosols in some cases (although again commonality of optical properties should not be taken to imply commonality of microphysical properties or origin).…”

Tropospheric ozone and its precursors from the urban to the global scale from air quality to short-lived climate forcer

“…Urban areas are dynamic regions in terms of emission of ozone precursors that have seen strong changes owing to emission reduction measures (see e.g. von Schneidemesser et al, 2011Schneidemesser et al, , 2010McMeeking et al, 2012;Warneke et al, 2012;Vijayaraghavan et al, 2014). …”

Regional Modeling of Aerosol Chemical Composition at the Puy de Dôme (France)

“…Les AOSA sont des polluants secondaires, ils ne proviennent pas directement d'une source polluante mais sont formés suite à l'oxydation de COV d'origine anthropique. Pendant le transport des masses d'air, les polluants secondaires sont formés ce qui explique leurs plus fortes concentrations en dehors des centre d'émissions (McMeeking et al, 2012 ;Freney et al, 2014). Ainsi, les niveaux d'AOSA simulés à la station du puy de Dôme résultent probablement de l'oxydation de COVA produits dans des zones fortement polluées.…”

“…Ces mesures aéroportées apportent des informations sur la distribution verticale des particules. Les mesures, au sol et en altitude, ont permis de mettre en évidence que les concentrations en aérosols organiques sont plus fortes dans la couche limite atmosphérique par rapport à la troposphère libre (Morgan et al, 2009 ;McMeeking et al, 2012 ;Crumeyrolle et al, 2013) ou encore que l'origine des masses d'air a une forte influence sur les concentrations massiques en aérosols organiques mesurées : ces concentrations étant plus importantes dans le cas de masses d'air ayant traversé durant leur transport des régions caractérisées par d'importantes activités anthropiques Freutel et al, 2013). Cependant, même si ces observations aident à identifier les sources et comprendre les processus physico-chimiques impliqués dans la formation des aérosols organiques, elles ne renseignent pas avec précision la distribution spatio-temporelle de ces particules.…”