Linking climate and air quality over Europe: effects of meteorology on PM_2.5 concentrations

Abstract. The effects of various meteorological parameters such as temperature, wind speed, absolute humidity, precipitation and mixing height on PM_2.5 concentrations over Europe were examined using a three-dimensional chemical transport model, PMCAMx-2008. Our simulations covered three periods, representative of different seasons (summer, winter, and fall). PM_2.5 appears to be more sensitive to temperature changes compared to the other meteorological parameters in all seasons.

PM_2.5 generally decreases as temperature increases, although the predicted changes vary significantly in space and time, ranging from −700 ng m⁻³ K⁻¹ (−8% K⁻¹) to 300 ng m⁻³ K⁻¹ (7% K⁻¹). The predicted decreases of PM_2.5 are mainly due to evaporation of ammonium nitrate, while the higher biogenic emissions and the accelerated gas-phase reaction rates increase the production of organic aerosol (OA) and sulfate, having the opposite effect on PM_2.5. The predicted responses of PM_2.5 to absolute humidity are also quite variable, ranging from −130 ng m⁻³ %⁻¹ (−1.6% %⁻¹) to 160 ng m⁻³ %⁻¹ (1.6% %⁻¹) dominated mainly by changes in inorganic PM_2.5 species. An increase in absolute humidity favors the partitioning of nitrate to the aerosol phase and increases the average PM_2.5 during summer and fall. Decreases in sulfate and sea salt levels govern the average PM_2.5 response to humidity during winter. A decrease of wind speed (keeping the emissions constant) increases all PM_2.5 species (on average 40 ng m⁻³ %⁻¹) due to changes in dispersion and dry deposition. The wind speed effects on sea salt emissions are significant for PM_2.5 concentrations over water and in coastal areas. Increases in precipitation have a negative effect on PM_2.5 (decreases up to 110 ng m⁻³ %⁻¹) in all periods due to increases in wet deposition of PM_2.5 species and their gas precursors. Changes in mixing height have the smallest effects (up to 35 ng m⁻³ %⁻¹) on PM_2.5 .

Regarding the relative importance of each of the meteorological parameters in a changed future climate, the projected changes in precipitation are expected to have the largest impact on PM_2.5 levels during all periods (changes up to 2 μg m⁻³ in the fall). The expected effects in future PM_2.5 levels due to wind speed changes are similar in all seasons and quite close to those resulting from future precipitation changes (up to 1.4 μg m⁻³). The expected increases in absolute humidity in the future can lead to large changes in PM_2.5 levels (increases up to 2 μg m⁻³) mainly in the fall due to changes in particulate nitrate levels. Despite the high sensitivity of PM_2.5 levels to temperature, the small expected increases of temperature in the future will lead to modest PM_2.5 changes and will not dominate the overall change.