Abstract:To understand the new variation features of acid rain pollution deeply in typical northern regions of China, the precipitation pH value and conductivity at Taishan Station during 1993-2021 and Tai’an Station during 2007-2021 are analyzed. On this basis, synchronous intensive observation data of precipitation chemistry which was performed from May 2018 to April 2019 are analyzed to get the contributions of below-cloud processes and long-distance transport to acid precipitation in the Mount Taishan Area. Combined with the results of earlier studies, the new situation and causes of acid rain in the Mount Taishan Area in recent years are investigated. The study results show that the annual precipitation pH value at Taishan Station varied in the range from 4.36 to 6.47 during 1993-2021, while that at Tai’an Station ranged from 4.73 to 6.66 during 2007-2021. Owing to the strong below-cloud scavenging effect at Tai’an Station, the neutralization effect of alkaline pollutants was more pronounced, leading to a significant reduction in precipitation acidity compared with that at Taishan Station. During 1993-2021, the precipitation acidity at Taishan Station experienced a phased variation process, i.e., weakening, intensifying, moderately weakening, and relatively stabilizing or slightly intensifying. The neutralization effect of alkaline pollutants exerted an important influence on the long-term variation trend of acid rain pollution. The concentration of SO2-4 in precipitation in the Mount Taishan Area decreased to approximately 50% of that from 2004 to 2008 and the SO2-4/NO-3 at Taishan Station dropped from 2.84-3.98 to 1.21, which indicates that the source of acid rain had shifted from SO2 dominated to SO2 and NOx dominated. It is noteworthy that the NO-3 concentration in precipitation at Taishan Station and Tai’an Station increased by approximately 47% and 20%, respectively, which was contrary to the decreasing trend of NOx emissions in the whole China and Shandong Province during the same period. Backward trajectory air mass analysis shows that the precipitation characteristics at Taishan Station were mainly affected by the pollution emissions from Shandong Province and its surrounding provinces, including the Beijing-Tianjin-Hebei Region and Inner Mongolia.