Effectiveness of Precursor Emission Reductions for the Control of Summertime Ozone and PM2.5 in the Beijing–Tianjin–Hebei Region under Different Meteorological Conditions

We used observed concentrations of air pollutants, reanalyzed meteorological parameters, and results from the Goddard Earth Observing System Chemical Transport Model to examine the relationships between concentrations of maximum daily 8-h average ozone (MDA8 O₃), PM_2.5 (particulate matter with diameter of 2.5 µm or less), and PM_2.5 components and 2-m temperature (T2) or relative humidity (RH), as well as the effectiveness of precursor emission reductions on the control of O₃ and PM_2.5 in Beijing–Tianjin–Hebei (BTH) under different summertime temperature and humidity conditions. Both observed (simulated) MDA8 O₃ and PM_2.5 concentrations increased as T2 went up, with linear trends of 4.8 (3.2) ppb °C⁻¹ and 1.9 (1.5) µg m⁻³ °C⁻¹, respectively. Model results showed that the decreases in MDA8 O₃ from precursor emission reductions were more sensitive to T2 than to RH. Reducing a larger proportion of volatile organic compound (VOC) emissions at higher T2 was more effective for the control of summertime O₃ in BTH. For the control of summertime PM_2.5 in BTH, reducing nitrogen oxides (NO_x) combined with a small proportion of VOCs was the best measure. The magnitude of reduction in PM_2.5 from reducing precursor emissions was more sensitive to RH than to T2, with the best efficiency at high RH. Results from this study are helpful for formulating effective policies to tackle O₃ and PM_2.5 pollution in BTH.