Photochemical reaction playing a key role in particulate matter pollution over Central France: Insight from the aerosol optical properties

Atmospheric particle is one of the major air pollutants, and believed to be important for air quality, radiative forcing and climate. Measurements of aerosol optical properties, size distribution and PM₁₀ concentration were conducted at Orleans, central France during spring (7 March to 25 April) and autumn (25 October to 5 December) 2013. The average values of aerosol scattering coefficient (b_sca), absorption coefficient (b_abs), single scattering albedo (SSA) at 532 nm and PM₁₀ concentration are 54.9 ± 58.2 Mm^-1, 10.6 ± 10.9 Mm^-1, 0.81 ± 0.10 and 30.6 ± 21.6 μg/m³ for the spring campaign, and 35.4 ± 36.7 Mm^-1, 3.9 ± 4.4 Mm^-1, 0.83 ± 0.13 and 17.4 ± 11.8 μg/m³ for the autumn campaign, respectively. During the whole observation, the air parcel transported from Atlantic Ocean plays a role in cleaning up the ambient air in Orleans, while the air mass coming from the Eastern Europe induces the pollution events in Orleans. In this study, a simple approach, which based on the diurnal variation of PM₁₀ concentration, Boundary layer depth (BLD) and the human activity factor derived from anthropogenic emission rate, was introduced to estimate the contribution of secondary aerosol to ambient aerosols. Our results show that secondary particles formation trigged by photochemical reactions and oxidations can contribute maximum of 64% and 32% for PM₁₀ mass concentration during the spring and autumn time, respectively. These results highlight that photochemical reactions can enhance the atmospheric oxidation capacity and may faster the secondary particle formation and then play an important role in air quality.