From ultrafine to coarse particles: variability and source apportionment of atmospheric aerosol levels in the urban Mediterranean climate

[eng] Air pollution is a major environmental and public health concern, especially in urban areas where both emission sources and population are concentrated. The pollution sources and the evolution of aerosols and gaseous pollutants once emitted into the atmosphere depend on geographical, climatological and meteorological conditions of the study area. In the Western Mediterranean Basin, the coastal city of Barcelona (Spain) is characterized by a warm dry climate, scarce precipitation and high urban density, as well as being geographically constrained by the coastal range thus hindering the dispersion of pollutants. Within this context, the intensive SAPUSS (Solving Aerosol Problems by Using Synergistic Strategies) campaign developed in October 2010 in Barcelona consisted on concurrent aerosol measurements at different sites in the city region, with the aim of studying the aerosol temporal variability and spatial distribution, progressively moving away from urban aerosol sources. Several sites were selected: Road Site (RS) and Urban Background (UB) were located on ground levels, whereas Torre Mapfre (TM) and Torre Collserola (TC), representative of the urban/suburban environment were located at certain height (150 m a.s.l. and 415 m a.s.I., respectively). Finally, the Regional Background site (RB) located 50 km from the city allowed for the study of the transport of urban emissions outside the city. Results from simultaneous measurements of aerosol size distributions at the RS, UB, TC and RB with a Scanning Mobility Particle Sizer (SMPS) were studied after performing a k-means cluster analysis on the combined data sets. This allowed the classification of all size distributions in 9 clusters: three clusters account for traffic conditions (30% of the time), three account for background pollution (54%) and three described specific special cases (16%). Traffic emissions heavily impact the closest sites, and some of these particles evaporate when the air mass move away from the traffic hot spots. The analysis of long term SMPS data sets in the high insolation urban environments of Barcelona, Madrid, Brisbane, Rome and Los Angeles also by k-means clustering analysis revealed traffic and nucleation events as the two most relevant sources of ultrafine particles (44-63% and 14-19% of the time, respectively). Moreover, nucleation particles accounted for 21% of total N, evidencing the importance of nucleation processes to ultrafine particles concentrations in high insolation urban areas. The urban nucleation events consist on particles bursts starting around midday and lasting 3-4 hours while growing to 20-40 nm, opposite to regional nucleation “banana shape” events which usually grow to larger sizes. Regarding the composition of the PM1 fraction (PM mass levels below 1 μm) at the RS and UB during SAPUSS, a source apportionment PMF analysis was carried out. The resulting 9 factors could be broadly grouped in the following categories: road traffic (23-36% of PM1 mass), industrial and shipping emissions (42%), secondary aerosols (29%) and biomass burning (1%). The joint analysis of organic and inorganic species was able to identify a high number of sources resulting in in a more complete and realistic study of the aerosol sources in Barcelona. The study of the PM10 fraction (PM mass levels below 10 μm) at the RS, UB, TM and TC during SAPUSS by means of a PMF source apportionment study enabled the assessment of the spatial variability in vertical and horizontal levels. The 8 resulting factors accounted for primary traffic emissions (Exhaust and wear and Road dust, 19- 38% of PM10 mass), primary inorganic aerosols (Mineral dust and Aged marine, 28- 39%), industry (Heavy oil and Industrial, 5-7%) and secondary aerosols (Sulphate and Nitrate,28-36%). The main factors influencing the different sources concentration at each site were: proximity to the emission source, air mass origin and meteorological parameters. The complete study of aerosol fractions affecting the urban area of Barcelona and similar urban environments (Madrid, Brisbane, Roma and Los Angeles), from ultrafine to coarse particles, enables the identification of the main sources affecting each size fraction in particular and aerosols in general. Owing to the results obtained and the different techniques applied, recommendations regarding air pollution studies and air quality measures have been proposed.[cat] La contaminació atmosfèrica en ambients urbans és motiu de preocupació pel seu impacte en el medi ambient i en la salut de la població. Les fonts d'emissió d'aerosols atmosfèrics i la seva evolució a l'atmosfera depenen de factors geogràfics així com de les condicions climàtiques i meteorològiques de l'àrea d'estudi. A la conca Mediterrània Occidental, i a la ciutat de Barcelona en particular, el clima càlid, l'escassa precipitació, l'alta densitat de població i determinats factors geogràfics que poden dificultar la dispersió dels contaminants i influenciar molt marcadament els nivells i composició dels aerosols. En aquest context es va desenvolupar la campanya intensiva SAPUSS (Solving Aerosol Problems by Using Synergistic Strategies) a Barcelona a l'octubre de 2010, que consistia en mesures simultànies d'aerosols a diversos llocs de la ciutat, amb l'objectiu d'estudiar la variabilitat espacial i temporal dels aerosols. L'estudi dels nivells d'aerosols en funció de la mida de les partícules a 4 ciutats més amb un clima d'alta insolació similar al de Barcelona (Madrid, Brisbane, Roma i Los Angeles) ha permès avaluar les fonts que afecten a la variabilitat de partícules ultrafines en aquests ambients urbans. En particular s'han estudiat les característiques dels episodis de nucleació urbans (formació de noves partícules), així com la seva freqüència. També s'han caracteritzat les principals fonts d'aerosols de diàmetre inferior a 1µm i 10 iim (PM1 i PM10, respectivament) en diverses ambients urbans de Barcelona durant SAPUSS. Això ha permès estudiar la variabilitat a nivells horitzontal i vertical dins l'atmosfera urbana. L'estudi de les fonts que afecten els aerosols de l' àrea urbana de Barcelona i ambients similars en funció de la seua mida (des de les ultrafines fins a les grolleres) ha permès identificar les principals fonts que afecten a cada fracció en particular i als aerosols en general i per tant proposar mesures aplicables per a l'avaluació i millora de la qualitat de l'air

Atmospheric particle size distributions in the Spanish Network of Environmental DMAs (REDMAAS)

The present work is a first approach to the study of the spatio-temporal variability of the submicrometer atmospheric aerosol in Spain. The aerosol measurements have been obtained simultaneously at seven monitoring stations that compose the REDMAAS network during two measurement campaigns corresponding to summer and winter seasons. In both summer and winter periods those measurement stations with a direct influence of anthropogenic emissions recorded the highest concentrations of particle number. In the summer campaign, the average daily pattern of the aerosol size distribution in the traffic and background urban stations was conditioned by the traffic emissions and secondary aerosol formation through photochemical reactions (new particle formation events, NPF). However, the secondary aerosol had a higher contribution to the aerosol total number concentration in the rural background and high-altitude stations. In the winter campaign, in all sampling sites with the exception of Izaña station, the traffic and domestic activity emissions had a greater contribution than secondary aerosol formation on particle number total concentration. New particle formation events were identified at all sites during the summer period, and at sites without direct influence of anthropogenic emissions during the winter campaign. Some aerosol shrinkage processes were also observed at the Madrid and El Arenosillo stations.This work has been financed by the Ministry of Science and Innovation (CGL2011-15008-E, CGL2010-1777, CGL2011-27020, CGL2014-52877-R & CGL2014-55230-R), Xunta de Galicia (GRC2013-047 potentially cofounded by ERDF) and the European Union Seventh Framework Programme (FP7/2007–2013) ACTRIS under grant agreement no. 262254

Phenomenology of high-ozone episodes in NE Spain

Ground-level and vertical measurements (performed using tethered and non-tethered balloons), 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. (according to modelling and non-tethered balloon measurements), 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 m−3 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 with the tethered balloons (900-1000 m a.g.l.) during the campaign, BC and O3 were often anti-correlated or unrelated, possibly due to a prevailing regional or even 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 non-tethered balloon data. Relatively low concentrations of ultrafine particles (UFPs) were found during the study, and nucleation episodes were only detected in the boundary layer. Two types of O3 episodes were identified: type A with major exceedances of the O3 information threshold (180 µg m−3 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 (or fumigation) of the polluted BMA/regional air masses (open circulation), and relatively lower O3 levels, but still exceeding the 8 h averaged health target. 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 VOC 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

Atmospheric Particle Size Distributions in the Spanish Network of Environmental DMAs (REDMAAS)

The present work is a first approach to the study of the spatio-temporal variability of the submicrometer atmospheric aerosol in Spain. The aerosol measurements have been obtained simultaneously at seven monitoring stations that compose the REDMAAS network during two measurement campaigns corresponding to summer and winter seasons. In both summer and winter periods those measurement stations with a direct influence of anthropogenic emissions recorded the highest concentrations of particle number. In the summer campaign, the average daily pattern of the aerosol size distribution in the traffic and background urban stations was conditioned by the traffic emissions and secondary aerosol formation through photochemical reactions (new particle formation events, NPF). However, the secondary aerosol had a higher contribution to the aerosol total number concentration in the rural background and high-altitude stations. In the winter campaign, in all sampling sites with the exception of Izaña station, the traffic and domestic activity emissions had a greater contribution than secondary aerosol formation on particle number total concentration. New particle formation events were identified at all sites during the summer period, and at sites without direct influence of anthropogenic emissions during the winter campaign. Some aerosol shrinkage processes were also observed at the Madrid and El Arenosillo stations.Peer reviewe

Phenomenology of high-ozone episodes in NE Spain

Ground-level and vertical measurements (performed using tethered and non-tethered balloons), 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 (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 mg-a.g.l. (according to modelling and non-tethered balloon measurements), 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 mg-3 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 with the tethered balloons (900-1000 m a.g.l.) during the campaign, BC and O3 were often anti-correlated or unrelated, possibly due to a prevailing regional or even 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 non-tethered balloon data. Relatively low concentrations of ultrafine particles (UFPs) were found during the study, and nucleation episodes were only detected in the boundary layer. Two types of O3 episodes were identified: type A with major exceedances of the O3 information threshold (180 μg mg-3 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 (or fumigation) of the polluted BMA/regional air masses (open circulation), and relatively lower O3 levels, but still exceeding the 8 h averaged health target. 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 VOC 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. © 2017 Author(s).The present work was supported by the Spanish Ministry of Economy and Competitiveness and FEDER funds under the project HOUSE (CGL2016-78594-R), by the Generalitat de Catalunya (AGAUR 2015 SGR33 and the DGQA). Part of this research was supported by the Korean Ministry of the Environment through “The Eco-Innovation project”. The participation of University of Marseille and University of Birmingham was partially supported by two TNA actions projects carried out under the ACTRIS2 project (grant agreement No. 654109) financed by the European Union’s Horizon 2020 research and innovation program. The support of the CUD of Zaragoza (project CUD 2013-18) is also acknowledged. We are very thankful to the Generalitat de Catalunya for supplying the air quality data from the XVPCA stations, to METEOCAT (the Meteorological Office of Catalonia) for providing meteorological data and to the IES J. Callís and the Meteorological Station from Vica (especially to Manel Dot) for allowing the performance of the vertical profiles and mobile unit measurements, respectively. In memoriam of Andrei LyasotaPeer reviewe

Vertical and horizontal fall-off of black carbon and NO2 within urban blocks

While exposure to traffic pollutants significantly decreases with distance from the curb, very dense urban architectures hamper such dispersion. Moreover, the building height reduces significantly the dispersion of pollutants. We have investigated the horizontal variability of Black Carbon (BC) and the vertical variability of NO and BC within the urban blocks. Increasing the distance from road BC concentrations decreased following an exponential curve reaching halving distances at 25 m (median), although with a wide variability among sites. Street canyons showed sharper fall-offs than open roads or roads next to a park. Urban background concentrations were achieved at 67 m distance on average, with higher distances found for more trafficked roads. Vertical fall-off of BC was less pronounced than the horizontal one since pollutants homogenize quickly vertically after rush traffic hours. Even shallower vertical fall-offs were found for NO. For both pollutants, background concentrations were never reached within the building height. A street canyon effect was also found exacerbating concentrations at the lowest floors of the leeward side of the road. These inputs can be useful for assessing population exposure, air quality policies, urban planning and for models validation

Phenomenology of high-ozone episodes in NE Spain

Ground-level and vertical measurements (performed using tethered and non-tethered balloons), 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. (according to modelling and non-tethered balloon measurements), 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 m−3 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 with the tethered balloons (900-1000 m a.g.l.) during the campaign, BC and O3 were often anti-correlated or unrelated, possibly due to a prevailing regional or even 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 non-tethered balloon data. Relatively low concentrations of ultrafine particles (UFPs) were found during the study, and nucleation episodes were only detected in the boundary layer. Two types of O3 episodes were identified: type A with major exceedances of the O3 information threshold (180 µg m−3 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 (or fumigation) of the polluted BMA/regional air masses (open circulation), and relatively lower O3 levels, but still exceeding the 8 h averaged health target. 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 VOC 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