Aerosol source apportionment uncertainty linked to the choice of input chemical components.

For a Positive Matrix Factorization (PMF) aerosol source apportionment (SA) studies there is no standard procedure to select the most appropriate chemical components to be included in the input dataset for a given site typology, nor specific recommendations in this direction. However, these choices are crucial for the final SA outputs not only in terms of number of sources identified but also, and consequently, in the source contributions estimates. In fact, PMF tends to reproduce most of PM mass measured independently and introduced as a total variable in the input data, regardless of the percentage of PM mass which has been chemically characterized, so that the lack of some specific source tracers (e.g. levoglucosan) can potentially affect the results of the whole source apportionment study. The present study elaborates further on the same concept, evaluating quantitatively the impact of lacking specific sources' tracers on the whole source apportionment, both in terms of identified sources and source contributions. This work aims to provide first recommendations on the most suitable and critical components to be included in PMF analyses in order to reduce PMF output uncertainty as much as possible, and better represent the most commons PM sources observed in many sites in Western countries. To this aim, we performed three sensitivity analyses on three different datasets across EU, including extended sets of organic tracers, in order to cover different types of urban conditions (Mediterranean, Continental, and Alpine), source types, and PM fractions. Our findings reveal that the vehicle exhaust source resulted to be less sensitive to the choice of analytes, although source contributions estimates can deviate significantly up to 44 %. On the other hand, for the detection of the non-exhaust one is clearly necessary to analyze specific inorganic elements. The choice of not analysing non-polar organics likely causes the loss of separation of exhaust and non-exhaust factors, thus obtaining a unique road traffic source, which provokes a significant bias of total contribution. Levoglucosan was, in most cases, crucial to identify biomass burning contributions in Milan and in Barcelona, in spite of the presence of PAHs in Barcelona, while for the case of Grenoble, even discarding levoglucosan, the presence of PAHs allowed identifying the BB factor. Modifying the rest of analytes provoke a systematic underestimation of biomass burning source contributions. SIA factors resulted to be generally overestimated with respect to the base case analysis, also in the case that ions were not included in the PMF analysis. Trace elements were crucial to identify shipping emissions (V and Ni) and industrial sources (Pb, Ni, Br, Zn, Mn, Cd and As). When changing the rest of input variables, the uncertainty was narrow for shipping but large for industrial processes. Major and trace elements were also crucial to identify the mineral/soil factor at all cities. Biogenic SOA and Anthropogenic SOA factors were sensitive to the presence of their molecular tracers, since the availability of OC alone is unable to separate a SOA factor. Arabitol and sorbitol were crucial to detecting fungal spores while odd number of higher alkanes (C27 to C31) for plant debris.

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 NO2 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 NO2. 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.

Particle-related exposure, dose and lung cancer risk of primary school children in two European countries.

Schools represent a critical microenvironment in terms of air quality due to the proximity to outdoor particle sources and the frequent lack of proper ventilation and filtering systems. Moreover, the population exposed in schools (i.e. children) represents a susceptible population due to their age. Air quality-based studies involving students' exposure at schools are still scarce and often limited to mass-based particle metrics and may thus underestimate the possible effect of sub-micron particles and particle toxicity. To this purpose, the present paper aims to evaluate the exposure to different airborne particle metrics (including both sub- and super-micron particles) and attached carcinogenic compounds. Measurements in terms of particle number, lung-deposited surface area, and PM fraction concentrations were measured inside and outside schools in Barcelona (Spain) and Cassino (Italy). Simultaneously, PM samples were collected and chemically analysed to obtain mass fractions of carcinogenic compounds. School time airborne particle doses received by students in classrooms were evaluated as well as their excess lung cancer risk due to a five-year primary school period. Median surface area dose received by students during school time in Barcelona and Cassino resulted equal to 110mm2 and 303mm2, respectively. The risk related to the five-year primary school period was estimated as about 2.9×10-5 and 1.4×10-4 for students of Barcelona and Cassino, respectively. The risk in Barcelona is slightly higher with respect to the maximum tolerable value (10-5, according to the U.S. Environmental Protection Agency), mainly due to toxic compounds on particles generated from anthropogenic emissions (mainly industry). On the other hand, the excess lung cancer risk in Cassino is cause of concern, being one order of magnitude higher than the above-mentioned threshold value due to the presence of biomass burning heating systems and winter thermal inversion that cause larger doses and great amount of toxic compounds on particles.

Outdoor and indoor particle characterization from a large and uncontrolled combustion of a tire landfill.

A large and uncontrolled fire of a tire landfill started in Seseña (Toledo, Spain) on May 13, 2016. An experimental deployment was immediately launched in the area for measuring regulated and non-standard air quality parameters to assess the potential impact of the plume at local and regional levels. Outdoor and indoor measurements of different parameters were carried out at a near school, approximately 700m downwind the burning tires. Real time measurements of ambient black carbon (BC) and total number particle concentrations were identified as good tracers of the smoke plume. Simultaneous peaks allowed us to characterize situations of the plume impact on the site. Outdoor total particle number concentrations reached in these occasions 3.8×105particlescm-3 (on a 10min resolution) whereas the indoor concentration was one order of magnitude lower. BC mass concentrations in ambient air were in the range of 2 to 7µgm-3, whereas concentrations<2µgm-3 were measured indoor. Indoor and outdoor deposited inhalable dust was sampled and chemically characterized. Both indoor and outdoor dust was enriched in tire components (Zn, sulfate) and PAHs associated to the tire combustion process. Infiltration processes have been documented for BC and particle number concentrations causing increases in indoor concentrations.

Secondary organic aerosol origin in an urban environment: influence of biogenic and fuel combustion precursors.

Source contributions of organic aerosol (OA) are still not fully understood, especially in terms of quantitative distinction between secondary OA formed from anthropogenic precursors vs. that formed from natural precursors. In order to investigate the OA origin, a field campaign was carried out in Barcelona in summer 2013, including two periods characterized by low and high traffic conditions. Volatile organic compound (VOC) concentrations were higher during the second period, especially aromatic hydrocarbons related to traffic emissions, which showed a marked daily cycle peaking during traffic rush hours, similarly to black carbon (BC) concentrations. Biogenic VOC (BVOC) concentrations showed only minor changes from the low to the high traffic period, and their intra-day variability was related to temperature and solar radiation cycles, although a decrease was observed for monoterpenes during the day. The organic carbon (OC) concentrations increased from the first to the second period, and the fraction of non-fossil OC as determined by (14)C analysis increased from 43% to 54% of the total OC. The combination of (14)C analysis and Aerosol Chemical Speciation Monitor (ACSM) OA source apportionment showed that the fossil OC was mainly secondary (>70%) except for the last sample, when the fossil secondary OC only represented 51% of the total fossil OC. The fraction of non-fossil secondary OC increased from 37% of total secondary OC for the first sample to 60% for the last sample. This enhanced formation of non-fossil secondary OA (SOA) could be attributed to the reaction of BVOC precursors with NOx emitted from road traffic (or from its nocturnal derivative nitrate that enhances night-time semi-volatile oxygenated OA (SV-OOA)), since NO2 concentrations increased from 19 to 42 µg m(-3) from the first to the last sample.

Seasonal and spatial variation of organic tracers for biomass burning in PM1 aerosols from highly insolated urban areas.

PM1 aerosol characterization on organic tracers for biomass burning (levoglucosan and its isomers and dehydroabietic acid) was conducted within the AERTRANS project. PM1 filters (N = 90) were sampled from 2010 to 2012 in busy streets in the urban centre of Madrid and Barcelona (Spain) at ground-level and at roof sites. In both urban areas, biomass burning was not expected to be an important local emission source, but regional emissions from wildfires, residential heating or biomass removal may influence the air quality in the cities. Although both areas are under influence of high solar radiation, Madrid is situated in the centre of the Iberian Peninsula, while Barcelona is located at the Mediterranean Coast and under influence of marine atmospheres. Two extraction methods were applied, i.e. Soxhlet and ASE, which showed equivalent results after GC-MS analyses. The ambient air concentrations of the organic tracers for biomass burning increased by an order of magnitude at both sites during winter compared to summer. An exception was observed during a PM event in summer 2012, when the atmosphere in Barcelona was directly affected by regional wildfire smoke and levels were four times higher as those observed in winter. Overall, there was little variation between the street and roof sites in both cities, suggesting that regional biomass burning sources influence the urban areas after atmospheric transport. Despite the different atmospheric characteristics in terms of air relative humidity, Madrid and Barcelona exhibit very similar composition and concentrations of biomass burning organic tracers. Nevertheless, levoglucosan and its isomers seem to be more suitable for source apportionment purposes than dehydroabietic acid. In both urban areas, biomass burning contributions to PM were generally low (2 %) in summer, except on the day when wildfire smoke arrive to the urban area. In the colder periods the contribution increase to around 30 %, indicating that regional biomass burning has a substantial influence on the urban air quality.

On the origin of water-soluble organic tracer compounds in fine aerosols in two cities: the case of Los Angeles and Barcelona.

Water-soluble organic compounds (WSOCs), represented by anhydro-saccharides, dicarboxylic acids, and polyols, were analyzed by gas chromatography interfaced to mass spectrometry in extracts from 103 PM1 and 22 PM2.5 filter samples collected in an urban background and road site in Barcelona (Spain) and an urban background site in Los Angeles (USA), respectively, during 1-month intensive sampling campaigns in 2010. Both locations have similar Mediterranean climates, with relatively high solar radiation and frequent anti-cyclonic conditions, and are influenced by a complex mixture of emission sources. Multivariate curve resolution-alternating least squares analyses were applied on the database in order to resolve differences and similarities in WSOC compositions in the studied sites. Five consistent clusters for the analyzed compounds were obtained, representing primary regional biomass burning organic carbon, three secondary organic components (aged SOC, isoprene SOC, and α-pinene SOC), and a less clear component, called urban oxygenated organic carbon. This last component is probably influenced by in situ urban activities, such as food cooking and traffic emissions and oxidation processes.

Deposition of semi-volatile organochlorine compounds in the free troposphere of the eastern North Atlantic Ocean.

Deposition samples were taken at a height of 2367 m above sea level (m.a.s.l.) on the Island of Tenerife from May 1999 until July 2000 and analysed for 19 polychlorinated biphenyl (PCB) congeners, hexachlorobenzene (HCB), hexachlorocyclohexanes (HCH) and DDTs. This site is located above the inversion layer, so samples represent background concentrations of the free troposphere. The average deposition fluxes of HCB, total HCH, DDTs and PCBs were 86, 400, 110 and 780 ng m(-2) yr(-1), respectively, being lower than those reported at sea level in continental or marine areas. All compounds are generally found in higher abundance in the wet precipitation samples. However, these samples only represent a fraction, e.g. 33%, of the total deposition load. Annual mass balance calculations show that wet precipitation is essentially responsible for the deposition of the low molecular weight OC whereas dry deposition accounts for more than 50% of the higher molecular weight PCBs.

Polychlorinated biphenyls and hexachlorobenzene in atmosphere, sea-surface microlayer, and water measured with semi-permeable membrane devices (SPMDs).

The time evolution of polychlorinated biphenyl (PCB) levels and hexachlorobenzene (HCB) levels in air, seawater, and at the sea-air boundary layer was examined during autumn and winter at a near-shore location in the Western Wadden Sea (Netherlands), using semi-permeable membrane devices (SPMDs). Performance reference compounds (PRCs) were added to the SPMDs prior to exposure for measuring the in situ exchange kinetics. For PCBs, a fair degree of equilibrium between atmosphere and water was found. HCB concentrations in the atmosphere were about eight times higher than the equilibrium concentration. PCB concentrations in seawater and atmosphere fell by a factor of 2-10, respectively, during the sampling period. HCB concentrations in water increased by a factor of 2. Atmospheric concentrations of HCB showed a decrease by a factor of about 10. Results for the sea-surface microlayer (SSM) deployment showed that the chemical activities at the air-water interface did not differ from those in deeper water layers. This means that the SSM was of no special toxicological significance in this study as far as PCBs and HCB are concerned.