Characterization of Aerosol Physical and Optical Properties at the Observatoire Pérenne de l’Environnement (OPE) Site

Abstract

The Observatoire Pérenne de l’Environnement (OPE) station is a rural background site located in North-Eastern France. Besides emissions from agricultural activities, the site is located far from local emissions but at an even distance from the intense emission zones of Western Germany to the north-east and the Paris area to the south-west. In the paper, we report and analyze almost six years of measurements (1 May 2012 to 31 December 2018) of the optical and physical properties of aerosol particles. Based on aerosol optical and physical measurements combined with air mass back-trajectories, we investigate the dependence of these properties on air mass type. Two distinct equivalent black carbon (EBC) sources—origins-fossil fuel (FF) and biomass burning (BB)— were identified. FF was the dominant source of EBC (>70%) but showed a very marked seasonal variation. BB fraction is found higher during the cold seasons in the order of 35% (0.1 µg m−3) against 17% (0.05 µg m−3) during the warm seasons. The highest EBC and N0.54–1.15 (particles whose diameter ranged from 0.54 to 1.15 µm) median concentrations were observed during the night time and during the cold seasons compared to the warmer seasons, indicating primary sources trapped within a thin boundary layer (BL). A different behavior is found for N10–550 (particles whose diameter ranged from 10 to 550 nm) and coarse mode particles (N1.15–4.5, i.e., particles whose diameter ranged from 1.15 to 4.5 µm) median concentrations, which were observed during the warm seasons compared to the cold seasons, indicating rather biogenic secondary sources for the smaller particles, and potentially primary biogenic sources for the coarse mode particles. The scattering and absorption coefficients and single scattering albedo (SSA) show the same seasonal variations like the ones of N0.54–1.15 concentrations, indicating that particles larger than 500 nm seemed to contribute the most to the optical properties of the aerosol.

A global analysis of climate-relevant aerosol properties retrieved from the network of Global Atmosphere Watch (GAW) near-surface observatories

“…Slightly greater median values are, nonetheless, observed during summer, when the atmospheric boundary layer (ABL) height is also increased relative to colder seasons. This suggests the presence of an additional source of aerosols in summer which compensates for the ABL height dilution effect, as recently discussed by Farah et al (2020), who moreover suggested a photochemical or biogenic source. The overall weak seasonality observed in lowland urban areas is likely related to the contribution of very local sources which do not have any strong seasonal cycle (e.g.…”

“…Variability for the in situ climate-relevant aerosol properties relevant to SARGAN is documented for many GAW stations. Integration of results from different sets of stations addressed different scales, from country (Sun et al, 2020) to continental (Sherman et al, 2015, Asmi et al, 2013Fountoukis et al, 2014;Zanatta et al, 2016;Cavalli et al, 2016;Crippa et al, 2014;Pandolfi et al, 2018), to global (Collaud Coen et al, 2013;Asmi et al, 2013;Andrews et al, 2011Andrews et al, , 2019Sellegri et al, 2019).…”

Seasonality of the particle number concentration and size distribution: a global analysis retrieved from the network of Global Atmosphere Watch (GAW) near-surface observatories

“…8). This is consistent with findings by Freud et al (2017) for size distributions measured at five Arctic sites.…”

Overview of the French Operational Network for In Situ Observation of PM Chemical Composition and Sources in Urban Environments (CARA Program)

“…Here, results obtained from this dense observation network are supplemented by complementary results acquired during a specific pluriannual research program focusing on air pollution sources and mechanisms in the Arve Valley of the French Alps (DECOMBIO, [14,15]). Data collected at the remote regional background site of the long-term Environmental Observatory (OPE, [16,17])-maintained by the agence nationale pour la gestion des déchets radioactifs (ANDRA)-has also been added for purposes of comparison with results from urban environments.…”