The PM2.5concentration characteristics of "2+26" cities in Beijing-Tianjin-Hebei and the surrounding region during the Spring Festival and the Lantern Festival in 2021 were analyzed. The average daily concentration and hourly concentration of PM2.5 in the three days before and after the Spring Festival and the Lantern Festival from 2016 to 2021 and the characteristics of the PM2.5 chemical components during the Spring Festival and the Lantern Festival from 2019 to 2021 were comparatively analyzed. In addition, the impact of meteorological factors on PM2.5 concentration from 2016 to 2021 and the key factors affecting the forecast result of Beijing during the Spring Festival in 2021 were discussed. The results showed that the combination of fireworks and firecrackers and adverse weather conditions resulted in a moderate to heavy pollution process during the Spring Festival in 2021 and a light to moderate pollution process during the Lantern Festival in "2+26" cities. The average ρ(PM2.5) was 111 μg·m-3. The hourly peak ρ(PM2.5) was 156 μg·m-3, which was the lowest in 2016 to 2021. The three days before and after the Lantern Festival in 2021, the average ρ(PM2.5) of "2+26" cities was 85 μg·m-3, and the hourly peak ρ(PM2.5) was 125 μg·m-3. During this period, the hour number of heavy and severe pollution was the lowest in 2016 to 2021. Component observation results showed that the impact of fireworks and firecrackers during the Spring Festival and the Lantern Festival in 2021 was gradually reduced, and the effect of bans and restrictions for fireworks and firecrackers was significant. The regional pollution was dominated by conventional pollution accumulation and nitrate. The concentration of organic matter in some cities during the Spring Festival was relatively high, which may be related to local industrial emissions and the impact of blasting fireworks and firecrackers. The comparative analysis of meteorological factors and PM2.5 concentration showed that the factors such as wind speed and direction, ground pressure, and relative humidity all affected PM2.5 concentration and the duration of the regional pollution process. The influence of oscillation of the boundary layer transport sink on diffusion conditions in the North China Plain, the location and intensity of the small high pressure in North China and the intensity of its high-altitude moving airflow, and the uncertainty of fireworks displays, as well as the low accuracy of weather forecasts caused by frequent weather changes during the alternate period of winter and spring, could affect the accuracy of air quality forecast results in the northern Beijing-Tianjin-Hebei region. In summary, although the impact of fireworks and firecrackers has been reduced in recent years, in order to improve the air quality, it is recommended to further strengthen the control of fireworks and firecrackers, especially outside the Beijing Fifth Ring Road and Beijing's surrounding cities.
Keywords: Beijing-Tianjin-Hebei region; PM2.5 chemical composition; fireworks and firecrackers; meteorological impacts; pollution characteristics; the Spring Festival; “2+26” cities.