Spatial and temporal variability of carbonaceous aerosol absorption in the Po Valley

Knowledge gaps in the optical properties of carbonaceous aerosols account for a significant fraction of the uncertainty of aerosol-light interactions in climate models. Both black carbon (BC) and brown carbon (BrC) can display a range of optical properties in ambient aerosol due to different sources and chemical transformation pathways. This study investigates the optical absorption properties of BC and BrC at an urban and a rural site in the Po Valley (Italy), a known European pollution hot spot. We observed spatial and seasonal variability of aerosol absorption coefficients, with the highest values measured in winter at the urban site of Milan (12 Mm–1 on average) and the lowest values in summer at the rural site of Motta Visconti (3 Mm–1 on average). The average aerosol Absorption Å ngström Exponent (AAE) measured during the two experiments across the 370–880 nm wavelength range was 1.1 and 1.2 at the urban and the rural site, respectively. The observed AAE values in winter (the average AAE during the two winter campaigns was 1.2) are consistent with the contribution of wood burning BrC, as confirmed by macro-tracer analysis. The BC mass absorption cross section (MACBC) did not show a specific seasonal or spatial variability across the two sites and maintained an average value of 10 ± 5 m2 g–1 at 880 nm. The optical properties of BrC, investigated off-line after extraction of organic aerosol (OA) indicate that wood burning was the dominant BrC source in winter, while secondary organic aerosol (SOA) from other anthropogenic emissions was the main source of BrC in summer

Determination of Local Source Profile for Soil Dust, Brake Dust and Biomass Burning Sources

Knowledge on the main emission sources and their relative importance is essential for policy makers to define effective pollution reduction strategies. Such knowledge can be gained by receptor modeling using e.g. the chemical mass balance model (CMB). For a successful application of CMB all important sources must be known and information must be available on representative emission profiles. Speciation profiles of emission sources can be found in literature and extensive databases are available (U.S. E.P.A., 2002). However, it is preferable to use profiles representing the actual sources present in the area whenever is possible. For the Lombardy region, previous studies have demonstrated the importance of soil and fugitive dust, biomass burning and brake lining dust (Regione Lombardia, ARPA Lombardia, Fondazione Lombardia per l¿Ambiente, 2008; AA.VV., 2006). The goal of this work is to report our methodology used to determine ¿local¿ source profiles of soil dust, domestic wood burning and brake lining dust, to be used for example in the CMB applications. To investigate the model sensitivity, simulations were carried out for several sites with different local and no-local profiles.JRC.DDG.H.4-Transport and air qualit

Daily patterns of the multi-modal structure of the particle number size distribution in Milan, Italy

Aerosol number concentration and size distributions in the 10e20,000 nm size range were measured using a Differential Mobility Particle Sizer (DMPS) and an Optical Particle Counter (OPC) at an urban background site. Daily patterns of the total particle (TP), ultrafine (UFP, Dp < 100 nm) and submicron (SMP, 100 < Dp < 1000 nm) fine particle concentration are analysed both on seasonal (cold and warm season) and weekly (weekdays and weekends) basis. TP number concentrations are in the orders of 104 cm³, with UFPs and SMPs accounting for 80% and 20%, respectively; the contribution of supermicron particles to TP number is negligible. The multi-modal structure of particle number size distributions (NSD) is investigated by fitting a multi-lognormal model to the observed size distributions in the submicron size range, where almost 100% of the TPs fall. Three lognormal components (1 located in the Aitken mode size range and 2 in the accumulation mode range) are usually present in the fitted model and the corresponding modal parameters and their daily pattern have been estimated. The Aitken mode particles increase simultaneously with primary traffic emissions, peaking on the morning rush hour and dominating the NSD still during the afternoon and on the evening rush hour. The smaller accumulation mode particles are influenced by the condensation and coagulation processes induced by the daily patterns of the boundary layer and of ambient temperature, becoming more and more important from the evening rush hour throughout the night and providing the largest contribution to TP number at late night.JRC.H.2-Climate change and air qualit

Sources of Carbonaceous Aerosol in the Amazon Basin

The quantification of sources of carbonaceous aerosol is important to understand their atmospheric concentrations and study possible effects on climate and air quality, in addition to develop mitigation strategies. In the framework of the European Aerosol Cloud Climate Interaction (EUCAARI) project fine and coarse aerosol particles were sampled from February to June (wet season) and from August to September (dry season) 2008 in the central Amazon basin. The mass of fine particles averaged 2.4 ug m-3 during the wet season and 4.2 ug m-3 during the dry season. The average coarse aerosol mass concentration during wet and dry periods was 7.9 and 7.6 ug m-3, respectively. The overall chemical composition of fine and coarse mass did not show any seasonality with the largest fraction of fine and coarse aerosol mass explained by organic carbon (OC); the average OC to mass ratio was 0.4 and 0.6 in fine and coarse aerosol modes, respectively. The mass absorbing cross section of soot was determined by comparison of elemental carbon and light absorption coefficient measurements and it was equal to 4.7 m2g-1 at 637 nm. Carbon aerosol sources were identified by Positive Matrix Factorization (PMF) analysis of thermograms: 42% of fine total carbon mass was assigned to biomass burning, 41% to secondary organic aerosol (SOA), and 17% to volatile species likely due to wood smoldering. In the coarse mode, primary biogenic aerosol par-ticles (PBAP) dominated the carbonaceous aerosol mass. The results confirmed the importance of PBAP on the global carbon budget. The source apportionment results were employed to evaluate the ability of global chemistry transport model to simulate carbonaceous aerosol sources in a regional background site. The comparison showed an overestimation of elemental carbon (EC) during the dry season and OC both during the dry and the wet periods. The overestimation was likely due to the overestimation of biomass burning emission inventories and SOA production.JRC.H.2-Air and Climat

Influence of semi- and intermediate-volatile organic compounds (S/IVOC) parameterizations, volatility distributions and aging schemes on organic aerosol modelling in winter conditions

This study presents a high–resolution (5 km) set of new simulations performed with CAMx v6.40 over the Po Valley area (Northern Italy), aimed to enhance organic aerosol (OA) levels prediction and to gain insight into the sensitivity of CAMx to different uncertain features of the input setup. In particular, we mainly investigated the role of (i) volatility distributions of organic emissions, (ii) parametrizations of semi– and intermediate–volatile organic compounds (S/IVOC) emissions and (iii) different aging schemes, by exploiting the latest experimental information available in the recent scientific literature. Model results were validated against two OA–specific datasets, available for both an urban site (Bologna, February 2013) and a rural one (Ispra, March 2013). We found out a remarkable performance enhancement of modelled OA levels when applying revisions in S/IVOC emission parametrizations together with the new volatility distributions, at both the validation sites. This performance enhancement is associated with a very significant improvement in secondary organic aerosol (SOA) prediction, mainly due to revised IVOC emissions. At Bologna urban site, mean fractional bias (MFB) of OA ranged from −80.1% in the worst run to −10.1% in the best one and index of agreement (IOA) from 0.52 to 0.75. Notable improvements but overall poorer metrics were found for Ispra site, where MFB ranges from −84.2% to −35% and IOA from 0.45 to 0.50. These findings indicate that organic matter in the semi– and intermediate–volatile range are most likely underestimated in official emission inventories for each main source category (i.e. biomass burning, diesel and gasoline vehicles exhaust). Finally, model results did not show a very pronounced sensitivity to aging processes, due to the low photochemical activity typically observed during winter–time. However, we give evidence that enabling aging processes for biomass burning related SOA, which is by default disabled in CAMx v6.40, can help in closing the gap between modelled and observed SOA concentrations.JRC.C.5-Air and Climat

AIRUSE-LIFE +: Estimation of natural source contributions to urban ambient air PM10 and PM2. 5 concentrations in southern Europe - Implications to compliance with limit values

The contribution of natural sources to ambient air particulate matter (PM) concentrations is often not considered; however, it may be significant for certain areas and during specific periods of the year. In the framework of the AIRUSE-LIFE+ project, state-of-the-art methods have been employed for assessing the contribution of major natural sources (African dust, sea salt and forest fires) to PM concentrations, in southern European urban areas. 24h measurements of PM10 and PM2.5 mass and chemical composition were performed over the course of a year in five cities: Porto, Barcelona, Milan, Florence and Athens. Net African dust and sea-salt concentrations were calculated based on the methodologies proposed by the EC (SEC 2011/208). The contribution of uncontrolled forest fires was calculated through receptor modelling. Sensitivity analysis with respect to the calculation of African dust was also performed, in order to identify major parameters affecting the estimated net dust concentrations. African dust contribution to PM concentrations was more pronounced in the eastern Mediterranean, with the mean annual relative contribution to PM10 decreasing from 21% in Athens, to 5% in Florence, and around 2% in Milan, Barcelona and Porto. The respective contribution to PM2. 5 was calculated equal to 14% in Athens and from 1.3 to 2.4% in all other cities. High seasonal variability of contributions was observed, with dust transport events occurring at different periods in the western and eastern Mediterranean basin. Sea salt was mostly related to the coarse mode and also exhibited significant seasonal variability. Sea-salt concentrations were highest in Porto, with average relative contributions equal to 12.3% for PM10. Contributions from uncontrolled forest fires were quantified only for Porto and were low on an annual basis (1.4 and 1.9% to PM10 and PM2. 5, respectively); nevertheless, contributions were greatly increased during events, reaching 20 and 22% of 24h PM10 and PM2. 5 concentrations, respectively. © Author(s) 2017.The authors gratefully acknowledge (i) the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model and READY website (http://www.ready.noaa.gov); (ii) the Barcelona Supercomputing Centre for the provision of the BSC-DREAM8b (Dust REgional Atmospheric Model) model (http://www.bsc.es/projects/earthscience/ BSC-DREAM/); and (iii) Andreas Stohl (NILU), Gerhard Wotawa and Petra Seibert (Institute of Meteorology and Geophysics, Vienna) and ECMWF (European Centre for Medium Range Weather Forecast) for the provision of FLEXTRA model. This work was funded by the AIRUSE LIFE+ (ENV/ES/584) EU project. Financial support from the EnTeC FP7 Capacities programme (REGPOT-2012-2013-1, FP7, ID: 316173) projects is also acknowledgedPeer reviewe

PM10 and PM2.5 Concentrations of chemical tracers for natural sources

The contribution of natural sources in particulate matter (PM) concentrations has been assessed for 5 Southern European cities: Porto (Portugal), Barcelona (Spain), Milan and Florence (Italy) and Athens (Greece). A database on the impact of natural source has been compiled, including concentrations of PM and chemical tracers used for the identification and quantification of African dust and sea salt contributions, as well as the calculated African net dust, and sea salt concentrations for each city. In addition, wildfires’ contribution is provided for Porto. Both PM10 and PM2.5 concentrations are reported for a total of six sites: Porto urban traffic site, POR-TR Barcelona urban background site, BCN-UB Milano urban background site, MLN-UB Florence urban background site, FI-UB Athens suburban site, ATH-SUB Athens urban traffic site, ATH-TR

Spatial and seasonal variability of carbonaceous aerosol across Italy

This paper analyses elemental (EC), organic (OC) and total carbon (TC) concentration in PM2.5 and PM10 samples collected over the last few years within several national and European projects at 37 remote, rural, urban, and traffic sites across the Italian peninsula