青藏高原周边黑碳和硫酸盐气溶胶的四季峰值变化及传输路径研究

Seasonal peak variations and transport pathways of black carbon and sulfate aerosols in the Qinghai-Xizang Plateau

关键词:  黑碳气溶胶  硫酸盐气溶胶  青藏高原  传输路径

Key words:  black carbon aerosol  sulfate aerosol  Qinghai-Xizang Plateau  transport pathways

摘要:

黑碳（BC）和硫酸盐（SO²⁻ ₄）等污染物气溶胶进入大气后能够影响地表辐射平衡和大气环境质量，经过大气环流传输后会对大范围环境造成污染，是全球气候环境变化的主导影响因素之一。为了弄清BC和 SO²⁻ ₄ 在青藏高原周边的时空峰值特征及其潜在传输路径，文章以2021年3月至2022年2月共12个月为研究时段，选择来源于资源环境科学数据平台的10个中国空气质量站点监测数据以及最靠近高原且能够反映气溶胶传输的3个站点，通过对比站点的PM10、PM_2.5等数据在研究时段的值，主要使用MERRA2数据集进行分析和讨论。结果显示：（1）青藏高原周边的SO²⁻ ₄ 和BC在冬春季浓度显著较高，并且SO²⁻ ₄ 的柱质量密度最高值 （80 mg/m² ）远高于BC（14 mg/m² ）；（2）印度半岛中东部近地面SO²⁻ ₄ 和BC浓度分别可达2.7 μg/kg、0.3 μg/kg， 中南半岛东部分别为1.6 μg/kg、0.8 μg/kg，均明显高于亚洲大部分区域，是显著的亚洲地区大气强污染源； （3）加深了污染物气溶胶向青藏高原传输的论点：随西风支流绕青藏高原以南，部分污染物从95°E往东， 30°N附近可跨越喜马拉雅南麓传输至青藏高原东南部地区；同时新发现表明，印度半岛和中南半岛偏南部的 BC、SO²⁻ ₄ 也可能由两地的气旋携带至高原以南。文章从遥感角度加深了污染物气溶胶对青藏高原影响的研究，认为有必要对印度半岛和中南半岛的污染物气溶胶进行长时间序列的监测，以期为未来国际生态策略的制定提供基础数据支撑。

Abstract:

Background, aim, and scope Aerosols such as black carbon (BC) and sulfate (SO²⁻ ₄ ), can influence the radiation balance and atmospheric quality upon entering the atmosphere, making them significant contributors to global warming and air pollution. Atmospheric circulation transports these aerosols, thereby extending their environmental impact far beyond the source regions. The aim of this study is to investigate the BC and SO²⁻ ₄ transport pathways, influence range and intensity around the Qinghai-Xizang Plateau (QXP). Materials and methods This study covers a 12-month period from March 2021 to February 2022. First, monitoring data from the China’s air quality monitoring sites were selected. By comparing PM10, PM_2.5, and other data values, the days with the most severe air pollution over the QXP and its adjacent areas were identified for each month. The column mass density (CMD) of BC and SO²⁻ ₄ , together with collocated wind flux data derived from the MERRA2 aerosol diagnostics dataset, were utilized to characterize the seasonal spatial distribution of BC and SO²⁻ ₄ and to identify their potential source regions. The AERONET (Aerosol Robotic NET work) global ground-based observations were used for auxiliary validation. Finally, the Aerosol Mixing Ratio (AMR) data from MERRA2 combined with CALIPSO lidar observations were used to reveal the vertical distribution characteristics of aerosols and to investigate their transport pathways. Results The results showed that BC and SO²⁻ ₄ around QXP exhibited higher concentrations and wider distribution in winter and spring. The CMD of BC can reach up to 14 mg/m² , whereas the CMD of SO²⁻ ₄ is significantly higher, reaching up to 80 mg/m² . In spring, the near-surface model of the AMR of SO²⁻ ₄ and BC data indicated that the east-central part of Indian Peninsula (2.7 μg/kg and 0.3 μg/kg) and the eastern part of the Indochinese Peninsula (1.6 μg/kg and 0.8 μg/kg) were the potential emission sources to the QXP. Aerosol pollutants primarily reach the QXP mainly through the southern slopes of the Himalayas. Additionally, the SO²⁻ ₄ and BC aerosols from the southern regions of the Indian Peninsula and the Indochinese Peninsula can be transported to the southern QXP by cyclones in these areas. Discussion Aerosol pollutants were frequently observed in the QXP and often interact with both local emissions and those from surrounding regions. The development of low-pressure systems at high altitudes is considered a key mechanism for enhancing the crossHimalayan transport of pollutants into the QXP, representing a major pathway for long-range atmospheric transport. Pollutants located at high altitudes over the southern Indochinese Peninsula have the potential to reach the Indian Peninsula. Moreover, pollutants originating from both ground level and high-altitude areas of the Indian Peninsula can be transported northward to the southern QXP. These findings suggest that the contribution of emissions from the Indochinese Peninsula and surrounding regions to pollutant levels in the QXP may have been underestimated in previous studies. Conclusions The concentrations of SO²⁻ ₄ and BC in the QXP were significantly higher in winter and spring, and SO²⁻ ₄ was much higher than BC. New discovery was that BC and SO2− 4 in the southern part of the Indian Peninsula and Indochinese Peninsula can be transported to south of the QXP by cyclones. Recommendations and perspectives In winter and spring, lower precipitation increases the transport efficiency of industrial and biomassburning aerosols from the Indian Peninsula and the Indochinese Peninsula to the QXP. Addressing this issue requires long-term, dynamic aerosol monitoring to build a scientific foundation for coordinated international environmental policies.