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Ground level and vertical measurements (coupled with modelling) of ozone (O3), other gaseous pollutants (NO, NO2, CO, SO2) and aerosols were carried out in the plains (Vic Plain) and valleys of the northern region of the Barcelona Metropolitan Area (BMA) in July 2015; an area typically recording the highest O3 episodes in Spain. Our results suggest that these very high O3 episodes were originated by three main contributions: (i) the surface fumigation from high O3 reservoir layers located at 1500-3000 m a.g.l., and originated during the previous day(s) injections of polluted air masses at high altitude; (ii) local/regional photochemical production and transport (at lower heights) from the BMA and the surrounding coastal settlements, into the inland valleys; and (iii) external (to the study area) contributions of both O3 and precursors. These processes gave rise to maximal O3 levels in the inland plains and valleys northwards from the BMA when compared to the higher mountain sites. Thus, a maximum O3 concentration was observed within the lower tropospheric layer, characterised by an upward increase of O3 and black carbon (BC) up to around 100-200 m a.g.l. (reaching up to 300 µg/m³ of O3 as a 10-s average), followed by a decrease of both pollutants at higher altitudes, where BC and O3 concentrations alternate in layers with parallel variations, probably as a consequence of the atmospheric transport from the BMA and the return flows (to the sea) of strata injected at certain heights the previous day(s). At the highest altitudes reached in this study (900-1000 m a.g.l.) during the campaign, BC and O3 were often anti-correlated or unrelated, possibly due to a prevailing regional/hemispheric contribution of O3 at those altitudes. In the central hours of the days a homogeneous O3 distribution was evidenced for the lowest 1 km of the atmosphere, although probably important variations could be expected at higher levels, where the high O3 return strata are injected according to the modelling results and free sounding data. Relatively low concentrations of ultrafine particles (UFP) were recorded in the 100-200 m a.g.l. atmospheric layer where concentrations of O3 were high; and nucleation episodes were only detected into the boundary layer. Two types of O3 episodes were identified: Type A) with major exceedances of the O3 information threshold (180 µg/m3 on an hourly basis) caused by a clear daily concatenation of local/regional production with accumulation (at upper levels), fumigation and direct transport from the BMA (closed circulation); and Type B) with regional O3 production without major recirculation (neither fumigation) of the polluted BMA/regional air masses (open circulation), and relatively lower O3 levels. The interpretation of OX (O3 + NO2) experimental data from strategically selected monitoring sites on the coast and inland, together with the photochemical modelling results have allowed to study the O3 phenomenology associated with the onset and development of severe episodes in the region of Catalonia in NE Spain. To implement potential O3 control and abatement strategies two major key tasks are proposed: (i) meteorological forecasting, from June to August, to predict recirculation episodes so that NOX and VOCs abatement measures can be applied before these episodes start; (ii) sensitivity analysis with high resolution modelling to evaluate the effectiveness of these potential abatement measures of precursors for O3 reduction. [ABSTRACT FROM AUTHOR]

As part of the European-funded IMPROVE LIFE project work programme experiments were performed in the Barcelona Metro system with the objective of better understanding the relationship between ventilation and air quality. The results demonstrate that tunnel ventilation plays an extremely important role in maintaining cleaner air and is capable of reducing both inhalable particulate matter (PM) mass and particle number concentration (> 0.3 μm) on platforms by over 50%, even in the presence of full-length platform screen doors. Another key influence on platform air quality is the chosen combination of fan power and forced air flow direction (impulsion of outdoor ambient air or extraction of subway indoor air): cleaner platform air was achieved using platform impulsion at higher power settings designed to ameliorate high summer temperatures underground. Reversing platform air flow from impulsion to extraction produced an immediate deterioration in PM air quality, most notably if the higher power setting was maintained, when an especially marked increase in numbers of very fine (submicron) particles was observed and attributed to tunnel air being drawn into the platform. At night, in the absence of trains and platform ventilation, platform air quality improves when tunnel fans are working at reduced power, whatever the flow direction (impulsion/extraction). Inside the air conditioned Barcelona Metro trains (where underground commuters spend most of their time) air quality is markedly better than on the platform, and unchanged A/C filters were observed capable of maintaining a similar reduction in inside train PM for at least three months. [ABSTRACT FROM AUTHOR]

New Delhi is one of the cities with the highest air pollution in the world. Huge efforts areundertaken to characterize the air pollution situation and to reduce or mitigate the impact onthe population and the environment. Modern instrumentation allows for a quantitativedetermination of aerosol concentration and composition with high time resolution (minutes tohours). We collected PM10 aerosols with an online X-ray fluorescence spectrometer in New Delhifrom January to March 2018 with hourly time resolution. Elements from Al to Pb wereanalyzed in near-real time. PM2.5 filters collected in parallel with 12 h time resolution wereanalyzed offline with ICP-OES and ICP-MS, and used for comparison and quality assessmentof the XRF data. The New Delhi winter period 2018 was characterized by generally weak winds and dry,warm weather, inducing a strong diurnal cycle of the atmospheric boundary layer. Thisinduced high PM concentrations during the night, with maxima in the early morning hours(around 07 h local time). Mean PM2.5 concentrations from 21 Jan through 15 Mar 2018 were142.5 μg m3, with peak hourly values of 411 μg m3. Individual elements in PM10reached extreme 1-h peak concentrations, e.g. Cl approximately 140 μg m3, or Pb 17μg m3. These values are consistent with other highly time-resolved data, but lessso with the 12-h PM2.5 filter data, and further analysis in this respect is needed.In general, filter elemental concentrations were smaller than the averaged XRFconcentrations. Whether the high Cl concentrations hint towards industrial sources or garbage burning(e.g. PVC) requires a detailed source apportionment, which will be performed once theoverall quality of the dataset has been established. [ABSTRACT FROM AUTHOR]