为了解内蒙古降水酸碱度的演变特征，使用全区酸雨站历史观测资料和气象要素、大气污染物浓度数据，分析降水pH值和酸雨、碱雨频率等时空分布特征及影响因素，其中碱雨阈值以酸雨为基准，定义为pH>8.4的降水。结果表明：（1） 由于内蒙古土壤酸碱度大多呈碱性且风沙缓冲作用较强，大部分地区碱性降水占比高于酸性降水，仅东北部的满洲里酸性降水占比更高；酸雨和碱雨发生概率较小，分别占总观测次数的1.1%和3.6%。（2） 降水pH值的空间分布表现为：中部>西部>东部的特征，近15 a（2007—2021年）年均降水pH值均值为6.2（满洲里）~7.2（锡林浩特），属于非酸雨区；近5 a内蒙古大部分地区酸雨、碱雨频率下降，仅乌拉特中旗的酸雨频率和阿拉善左旗的碱雨频率上升较明显。（3） 降水pH低值多出现在夏季汛期6—9月，高值在春季4—5月和冬季1—2月，这与地表植被覆盖度、降水量、风速风向、沙尘和寒潮等因素密切相关；另外，由于采暖期燃煤释放SO₂和NO_x等酸性气体，在呼和浩特、通辽等大气污染物浓度较高的地区，冬春季也存在降水pH值偏低的情况。

This study was established to understand the evolution of precipitation pH in Inner Mongolia since the 1990s, using the observation data of acid rain stations in Inner Mongolia, as well as meteorological elements and atmospheric pollutant concentration data, along with statistical analysis of the spatial and temporal distribution characteristics and factors influencing precipitation pH, and the frequencies of acid rain and alkali rain. The threshold of alkali rain refers to acid rain, which is defined as precipitation with pH >8.4. The conclusions are as follows: (1) Owing to the soil pH in Inner Mongolia mostly being alkaline and there being a strong buffering effect of wind sand, the proportion of alkaline precipitation is higher than that of acidic precipitation in most of Inner Mongolia, while the proportion of acidic precipitation is higher in Manzhouli in the northeast. The occurrence of acid rain and alkali rain accounted for 1.1% and 3.6%, respectively, having a low probability of occurrence. (2) The spatial distribution of the pH of precipitation shows the following order: central > western > eastern. The average annual precipitation pH range of the Inner Mongolia acid rain stations in the studied 15 years was 6.2 (Manzhouli) to 7.2 (Xilinhot), reflecting that this is not a highly acid rain-affected region. In the last 5 years, the frequency of acid rain and alkali rain has decreased in most areas, but the frequency of acid rain in Urad Middle Banner and alkali rain in Alxa Left Banner has increased significantly. (3) Low pH of precipitation mostly occurs from June to September in the summer flood season, and high pH mostly occurs from April to May in spring and January to February in winter, being closely related to vegetation coverage, precipitation, wind speed and direction, dust, and cold waves, among other factors. In addition, owing to the release of acidic gases such as SO₂ and NO_x from coal burning for heating during cold periods, the pH of precipitation is also low in winter and spring in Hohhot, Tongliao, and other regions with relatively high concentrations of air pollutants.