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This work investigates the variability of ozone (O3), carbon monoxide (CO) and equivalent black carbon (BC) at the Italian Climate Observatory "O. Vittori" (ICO- OV), part of the Mt. Cimone global GAW-WMO station (Italy). For this purpose, ICO-OV observations carried out in the period January 2007-June 2009, have been analyzed and correlated with the outputs of the FLEXPART Lagrangian dispersion model to specifically evaluate the influence of biomass burning (BB) and anthropogenic emissions younger than 20 days. During the investigation period, the average O3, CO and BC at ICO-OV were 54±3ppb, 122±7ppb and 213±34 ng m-3 (mean±expanded uncertainty with p < 95 %), with clear seasonal cycles characterized by summer maxima and winter minima for O3 and BC and spring maximum and summer minimum for CO. According to FLEXPART outputs, BB impact is maximized during the warm months from July to September but appeared to have a significant contribution to the observed tracers only during specific transport events. We characterised in detail five "representative" events with respect to transport scales (i.e. global, regional and local), source regions and O3, CO and BC variations. For these events, very large variability of enhancement ratios O3/CO (from -0.22 to 0.71) and BC/CO (from 2.69 to 29.83 ng m-3 ppb-1) were observed. CO contributions related with anthropogenic emissions (COant) contributed to 17.4 % of the mean CO value observed at ICO-OV, with the warm months appearing particularly affected by transport events of air-masses rich in anthropogenic pollution. The proportion of tracer variability that is described by FLEXPART COant peaked to 37% (in May-September) for CO, 19% (in May-September) for O3 and 32 % (in January-April) for BC. During May-September, the analysis of the correlation among CO, O3 and BC as a function of the COant indicated that ICO-OV was influenced by air-masses rich in anthropogenic pollution transported from the regional to the global scale. On the other side, CO and O3 were negatively correlated during October-December, when FLEXPART does not show significant presence of re- cent anthropogenic emissions and only a few observations are characterized by enhanced BC. Such behaviour may be attributed to an ensemble of processes concurrent in enhancing O3 with low CO (upper troposphere/lower stratosphere intrusions) and to O3 titration by NO in polluted air-masses along with lower photochemical activity. An intermediate situation occurs in January-April when CO and O3 were almost uncorrelated and BC enhancements were associated to relatively old (10 days) anthropogenic emissions. [ABSTRACT FROM AUTHOR]

This work introduces an index to identify deep stratospheric intrusions (SI) from measurement data alone, without requiring additional model-based information. This stratospheric intrusion index (SI2) provides a qualitative description of SI event behaviour by summarizing the information from different tracer variations. Moreover, being independent from any model constraint, the SI2 can also represent a valid tool to help in evaluating the capacity of chemistry-transport and chemistry-climate models in simulating deep stratosphere to troposphere transport. The in situ variations of ozone, beryllium-7 and relative humidity were used to calculate the index. The SI2 was applied on 8-year data recorded at the regional GAW station of Mt. Cimone (2165 m asl; 44.10N, 10.70E: Italy). The comparison of the SI2 behaviour with a pre-existing database obtained by also using model products, permitted us to tune a SI2-threshold value capable of identifying SI events efficiently. In good agreement with previous climatological studies across Europe, at Mt. Cimone, the averaged monthly SI frequency obtained by the SI2 analysis showed a clear seasonal cycle with a winter maximum and a spring-summer minimum. These results suggest that the presented methodology is efficient for both identifying SI events and evaluating their annual frequency at the considered baseline measurement site. [ABSTRACT FROM AUTHOR]

High levels of trace gas (O3 and CO) and aerosol (BC, fine and coarse particle volumes), as well as high scattering coefficient (σp) values, were recorded at the regional GAW-WMO station of Mt. Cimone (CMN, 2165 m a.s.l., Italy) during the period 26-30 August 2007. Analysis of air-mass circulation, aerosol chemical characterization and trace gas and aerosol enhancement ratios (ERs), showed that high O3 and aerosol levels were likely linked to (i) the transport of anthropogenic pollution from northern Italy, and (ii) the advection of air masses rich in mineral dust and biomass burning (BB) products from North Africa. In particular, during the advection of air masses from North Africa, the CO and aerosol levels (CO: 175 ppbv, BC: 1015 ng/m³, fine particle volume: 3.00μm³ cm-3, σp: 84.5 Mm-1) were even higher than during the pollution event (CO: 138 ppbv, BC: 733 ng/m³, fine particles volume: 1.58 μm³ cm-3, σp: 44.9 Mm-1). Moreover, despite the presence of mineral dust able to affect significantly the O3 concentration, the analysis of ERs showed that the BB event represented an efficient source of fine aerosol particles (e.g. BC), but also of the O3 recorded at CMN. In particular, the calculated O3/CO ERs (0.10-0.17 ppbv/ppbv) were in the range of values found in literature for relatively aged (2-4 days) BB plumes and suggested significant photochemical O3 production during the air-mass transport. For fine particles and σp, the calculated ERs was higher in the BB plumes than during the anthropogenic pollution events, stressing the importance of the identified BB event as a source of atmospheric aerosol able to affect the atmospheric radiation budget. These results suggest that episodes of mineral dust mobilization and wildfire emissions over North Africa could significantly influence radiative properties (as deduced from σp observations at CMN) and air quality over the Mediterranean basin and northern Italy. [ABSTRACT FROM AUTHOR]

Abstract: In the frame of the MIUR-AEROCLOUDS project (Study of Direct and Indirect Aerosol Effects on Climate), night-time and daytime size-segregated aerosol samples were collected concurrently at five different sites (near-city, urban, rural, marine and mountain background sites). The paper reports on the daily evolution of the main aerosol chemical characteristics as a function of particle size in different environments over the Italian Peninsula, spanning from the Po Valley to the south Tyrrhenian coast. Two 4-day intensive observation periods (IOPs) were undertaken in July 2007 and February 2008, under meteorological conditions typical of the summer and winter climate for Italy. In the summer IOP, under stable atmospheric conditions, at the low-altitude continental sites the diurnal evolution of the planetary boundary layer (PBL), induces an atmospheric dilution effect driving the particulate matter (PM) concentrations, while, at the mountain site, it determines the upward motion of polluted air masses from the Po Valley PBL in daytime. The fine fraction was dominated by ammonium salts and carbonaceous matter (water-soluble organic matter, WSOM, and water-insoluble carbonaceous matter, WINCM). High concentrations of ammonium sulphate and WSOM due to enhanced photochemical activity constituted the background aerosol composition over the whole country, whereas, ammonium nitrate and WINCM were more associated to local emissions (e.g. urban site with concentrations peaking in the finest size range due to strong local traffic-related sources of ultrafine particles). During the winter IOP in the Po Valley, the shallow PBL depths and low wind velocity, especially at night, favoured the condensation of semi-volatile species (i.e. organic matter and ammonium nitrate), causing the high fine PM concentration observed at ground level. [ABSTRACT FROM AUTHOR]