Abstract. As part of the Mediterranean Intensive Oxidant Study (MINOS) performed during August 2001 in the Eastern Mediterranean Region, intensive measurements of chemical and radiative properties of atmospheric aerosols were performed at two remote sites on Crete Island, located in the marine boundary layer (MBL), and in the lower free troposphere (FT), respectively. Gravimetric particulate mass, as well as chemically-derived masses of water soluble ions, organic and elemental carbon, and tracer elements for dust aerosols were measured for fine (<1.2 µm) and coarse (>1.2 µm) particles at the two sampling sites. Although strongly bound water, mainly associated with inorganic species, could have slightly altered our results (10% of the reconstructed mass), chemical mass closure was achieved most of the time for the fine and coarse size fractions and at both sites. Our conversion factor of 2.1 for organic carbon (OC) to particulate organic matter (POM) is at the upper end of those reported in the literature, but fits with the aged smoke particles collected during the campaign. The results indicate that this conversion factor changed during the campaign along with the BC/TC ratio. The particulate mass (PM) concentration for fine aerosols at the MBL and FT sites averaged 17.4±4.7 µg/m3 and 11.2±3.2 µg/m3, respectively, and is among the highest reported in the literature for remote sites; more than 90% of this PM was composed equally of ammonium sulfate and carbonaceous aerosols. Comparison between the MBL and FT sites showed a slight vertical gradient for PM that was not observed for dust aerosols, which averaged 10.5±4.8 and 11.7±5.0 µg/m3 for the MBL and FT sites, respectively. The results were used to reconstruct the ambient light scattering coefficient (σsp) that was measured at ambient Relative Humidity (RH) for fine particles at the MBL site. Reconstruction of σsp was achieved using ratios of wet to dry scattering, f(RH), that depend on RH for ammonium sulfate, but are kept equal to 1 for POM. This results in a low water adsorption for our organic-rich carbonaceous aerosols, although these aged biomass smoke aerosols are supposed to be highly oxidized. Mass scattering efficiencies of the main aerosol components were obtained by multivariate regression analysis, and were 2.66 and 4.19 m2/g (at the 95% confidence level) for dry ammonium sulfate and POM, respectively. The calculations indicate that one third of the reconstructed σsp was due to water uptake by ammonium sulfate aerosols, demonstrating their major role in the radiative aerosol properties in the eastern Mediterranean.

Abstract. During the major part of the Mediterranean Intensive Oxidant Study (MINOS) campaign (summer 2001, Crete Isl.), the Marine Boundary Layer (MBL) air was influenced by long range transport of biomass burning from the northern and western part of the Black Sea. During this campaign, carbonaceous aerosols were collected on quartz filters at a Free Tropospheric (FT) site, and at a MBL site together with size-resolved distribution of aerosols. Three Evolution Gas Analysis (EGA) protocols have been tested in order to better characterize the collected aged biomass burning smoke: A 2-step thermal method (Cachier et al., 1989) and a thermo-optical technique using two different temperature programs. The later temperature programs are those used for IMPROVE (Interagency Monitoring of Protected Visual Environments) and NIOSH 5040 (National Institute of Occupational Safety and Health). Artifacts were observed using the NIOSH temperature program and identified as interactions between carbon and dust deposited on the filter matrix at high temperature (T=550°C) under the pure helium step of the analysis. During the MINOS campaign, Black Carbon (BC) and Organic Carbon (OC) concentrations were on average respectively 1.19±0.56 and 3.62±1.08 μgC/m3 for the IMPROVE temperature program, and 1.09±0.36 and 3.75±1.24 μgC/m3 for the thermal method. Though these values compare well on average and the agreement between the Total Carbon (TC) measurements sample to sample was excellent (slope = 1.00, r2=0.93, n=56), important discrepancies were observed in determining BC concentrations from these two methods (average error of 33&amp;plusmn22%). BC from the IMPROVE temperature program compared well with non-sea-salt potassium (nss-K) pointing out an optical sensitivity to biomass burning. On the other hand, BC from the thermal method showed a better agreement with non-sea-salt sulfate (nss-SO4), considered as a tracer for fossil fuel combustion during the MINOS campaign. The coupling between these two methods for determining BC brings here new insights on the origin of carbonaceous aerosols in a complex mixture of different sources. It brings also to our attention that important deviations in BC levels are observed using three widely used EGA techniques and most probably none of the EGA tested here are well adapted to fully characterize this aerosol mixture. Spherical, smooth and silico-aluminated fly-ash observed by Analytical Scanning Electron Microscope (ASEM) confirm the influence of coal combustion on the carbonaceous aerosol load throughout the campaign. A raw calculation based on BC/nss-SO4 mass ratio suggests that biomass burning could be responsible for half of the BC concentration recorded during the MINOS campaign. From the plot of BC as a function of TC, two linear correlations were observed corresponding to 2 times series (before and after 12 August). Such good correlations suggest, from a first look, that both BC and OC have similar origin and atmospheric transport. On the other hand, the plot of BC as a function of TC obtained from the 2-step thermal method applied to DEKATI Low Pressure Cascade Impactor samples does not show a similar correlation and points out a non conservative distribution of this ratio with 2 super micron modes enriched in OC, correlated with sea salt aerosols and probably originating from gas-to-particle conversion.