Analysis of PM_2.5 variation characteristics and main influencing factors in the Yangtze River Basin from 2016 to 2021

Studying the variation characteristics and main influencing factors of PM_2.5 concentration in the Yangtze River Basin from 2016 to 2021 could provide references for optimizing the policy of collaborative governance of the atmospheric environment in the basin. Using the PM_2.5 concentration data from 110 national stations in the Yangtze River Basin from 2016 to 2021, the temporal and spatial variation characteristics of PM_2.5 were analyzed with the Theil-Sen trend analysis and Mann-Kendall statistical test methods. Combined with the Environmental Meteorological Assessment Index (EMI), the relative contributions of the two main influencing factors including the meteorological conditions and emission reduction measures, to the changes in PM_2.5 concentration changes during the "13th Five-Year Plan" period (2016—2020) and the first year of the "14th Five-Year Plan" (2021) were quantitatively analyzed. The results were as follows. (1) Significant spatial variations in PM_2.5 concentration distribution were found in the Yangtze River Basin was uneven in 2016-2021. The high-value areas were in the eastern part of the Hanjiang River Basin extending southward to the eastern part of the Dongting Lake Basin and the southern part of the Mintuo River, While the low-value area was in the upper and middle reaches of the Jinsha River Basin. (2) During the "13th Five-Year Plan" period, PM_2.5 concentration in major cities of the Yangtze River Basin decreased year by year, with an annual variation rate of -3.62μg·m^-3·a^-1. However, PM_2.5 concentration about 40% of the Yangtze River Basin region increased in 2021, which was mainly distributed in the upper reaches of the Yangtze River Basin and Dongting Lake Basin. (3) The PM_2.5 in the western part of the basin was greatly affected by meteorological conditions, while the eastern part was greatly affected by emission sources and other factors. (4) Meteorological conditions and emission reduction measures during the "13th Five-Year Plan" period were conducive to the decrease of PM_2.5 concentration.Their contribution rates to the increase of PM_2.5 were -16.54% and -14.00%, respectively. Compared with the previous year, the emission reduction measures in 2021 were generally beneficial to the decrease of PM_2.5 concentration (contribution rate of -5.84%), but adverse meteorological conditions (contribution rate of 4.49 %) offset part of the emission reduction effects, making a slight decrease in the PM_2.5 concentration.