Control of PM2.5 in Guangzhou during the 16th Asian Games period: Implication for hazy weather prevention

One factor causing the high frequency of hazy weather occurrence was the increased relative humidity during the Asian Games period. To avoid hazy weather occurrence, new PM2.5 standard was recommended based on visibility calculations using three available aerosol hygroscopic curves previously obtained for this city. The recommended PM2.5 standard was 63 μg m− 3 under dry condition and lower than 42 μg m− 3 under humid condition (RH ≥ 70%). These recommended values were much stricter than the NAAQS value of 75 μg m− 3. To reach the new standard, more rigorous control measures for coal industries should be established in the Pearl River Delta (PRD) region.