Abstract
Abstract. Detailed investigations of the chemical and microphysical properties of atmospheric aerosol particles were performed at the puy-de-Dôme (pdD) research station (1465 m) in autumn (September and October 2008), winter (February and March 2009), and summer (June 2010) using a compact Time-of-Flight Aerosol Mass Spectrometer (cToF-AMS). Over the three campaigns, the average mass concentrations of the non-refractory submicron particles ranged from 10 μg m−3 up to 27 μg m−3. Highest nitrate and ammonium mass concentrations were measured during the winter and during periods when marine modified airmasses were arriving at the site, whereas highest concentrations of organic particles were measured during the summer and during periods when continental airmasses arrived at the site. The measurements reported in this paper show that atmospheric particle composition is strongly influenced by both the season and the origin of the airmass. The total organic mass spectra were analysed using positive matrix factorisation to separate individual organic components contributing to the overall organic particle mass concentrations. These organic components include a low volatility oxygenated organic aerosol particle (LV-OOA) and a semi-volatile organic aerosol particle (SV-OOA). Correlations of the LV-OOA components with fragments of m/z 60 and m/z 73 (mass spectral markers of wood burning) during the winter campaign suggest that wintertime LV-OOA are related to aged biomass burning emissions, whereas organic aerosol particles measured during the summer are likely linked to biogenic sources. Equivalent potential temperature calculations, gas-phase, and LIDAR measurements define whether the research site is in the planetary boundary layer (PBL) or in the free troposphere (FT)/residual layer (RL). We observe that SV-OOA and nitrate particles are associated with air masses arriving from the PBL where as particle composition measured from RL/FT airmasses contain high mass fractions of sulphate and LV-OOA. This study provides unique insights into the effects of season and airmass variability on regional aerosol particles measured at an elevated site.
Highlights
Submicron atmospheric aerosols exert a highly uncertain effect on radiative climate forcing and can have serious impacts on human health
We show a high contribution of secondary organic aerosol particles similar to that of fulvic acid during all campaigns, but during the winter campaign the low volatility oxygenated organic aerosol particle (LV-oxidised organic aerosol (OOA)) mass spectra contains marker peaks of wood burning (Alfarra et al, 2007) (m/z 60 and m/z 73) and correlates strongly with the time series of m/z 73 and m/z 60
Lowest values of θ e are related to low CO/NOx ratios (Fig. 7) indicating that, overall, the thermodynamical indicator of BL/FT air masses, θe, is coherent with the chemical aging indicator, CO/NOx. These plots suggest that boundary layer air masses can be characterized by low θe and low CO/NOx ratios, whereas airmasses arriving from the free troposphere or residual layer are characterized by high θ e and high CO/NOx ratios (Fig. 7). If these plots are coloured by particle composition, we observe that high concentrations of NO3 and semi-volatile organic aerosol particle (SV-OOA) are most often related to airmasses mostly associated to BL air, whereas highest concentrations of low-volatility organic aerosol (LVOOA) are related to air masses associated to residual layer or free tropospheric air
Summary
Submicron atmospheric aerosols exert a highly uncertain effect on radiative climate forcing and can have serious impacts on human health. Similar to previous observations they showed that organic compounds were the most abundant species in the submicron particle fraction, with biomass burning organic aerosol particles being important during the winter and low-volatility organic aerosol (LVOOA) dominating during the spring and summer. These studies provide information on the background composition during different seasons they are unable to provide information on the seasonal variability at the same site. The focus of this study was to characterise the seasonal variability in the chemistry of both long-range transported and less aged PBL airmasses with high-time resolution, and thereby offering insights into the sources and properties of aerosol particles arriving at an elevated background site
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