大气中酸性超细粒子的测定方法和污染特征研究

Atmospheric particulate pollution is a major public concern due to the fact that particulate matters are closely related to human respiratory health, visibility reduction, eco-environmental damage and global climate. The size of particles is directly linked to their potential for causing health problems. The adverse effects of particles with diameter less than 10 µm (PM10) and less than 2.5µm (PM2.5) have been widely studied and well recognized in the past decades. Recently, more and more studies have found that much smaller particles such as ultrafine particles (< 100nm in diameter) in the air may be more important than PM2.5 and PM10 to cause adverse health effects, because they normally contain trace elements and toxins and can lodge deep into the lungs and some may get into the bloodstream, owing to the high diffusion coefficients of the particles. Another fact is that more than 90% of all airborne particles, both outdoors and indoors, when measured by number concentration, are generally found to be ultrafine particles. Therefore, people have high risk of exposure to these ultrafine particles which can affect both lungs and heart. Although growing epidemiological data indicates consistent and coherent associations between ambient ultrafine particles and health decrements such as mortality and morbidity, it is unlikely that all components of ultrafine particles are equally toxic. In fact, sulfuric acid and ammonium bisulfate, both strongly acidic, are important components of ultrafine particles in the air. Indeed, accumulated evidence strongly suggests that the number of acid-containing ultrafine particles is more closely correlated with total mortality, morbidity and hospital admissions for respiratory diseases. Environmental effects of acidic particle pollution include reduced visibility, environmental damage, and climate change. Thus, it is critical to be able to distinguish between the number of acidic ultrafine particles and the total number of ultrafine particles. It will provide useful data to air quality scientists, epidemiologists and policy makers to better understand the interplay among air pollution, climate change and human health. Based on the reasons mentioned above, therefore, the specific scientific objectives are:. To develop a new method for measuring number concentrations and size distributions of acidic ultrafine particles in the atmosphere;. To carry out field measurements at roadside, residential and background sites in Beijing to assess the reliability and efficiency of the sampling method and to improve our understanding of the temporal-spatial distribution of AUFPs in Beijing areas;. To utilize the source apportionment analysis to identify the possible sources of AUFPs in different areas of Beijing;. To study the formation mechanism of AUFPs using the aerosol thermodynamics equilibrium model.. The product developed in this project will significantly improve our capacity on the measurement of acidic ultrafine particles; further will be widely applied to the fields of air quality research, epidemiological study, toxicology, and environmental protection and management for better air pollution control.

大气气溶胶中的超细粒子由于粒径小（<100nm），扩散性强，可以直接进到人类的肺部肺泡甚至是血液内，导致比PM2.5和PM10更严重的健康危害。而且气溶胶粒子粒径越小、酸度越高，酸性的超细粒子由于具有强腐蚀性，对人体的危害更大。另外，由于很多非均相大气化学反应过程受气溶胶酸度的影响，研究大气酸性超细粒子的分布对大气化学研究显得尤为重要。因此，本项目以研究大气中酸性超细粒子的酸度、数量和粒径分布特征为目的，研发一套新的检测方法用于测量大气中酸性细粒子的数量浓度和粒径分布。在北京不同功能区域设置采样点（如商业住宅区、交通枢纽区、城市背景区），研究酸性细粒子的污染水平及时空分布，获得不同区域、不同季节的酸性粒子的分布规律并进行来源解析，同时在灰霾形成过程中研究酸性气溶胶的作用。本研究将为流行病学、空气质量模拟（如酸沉降、二次气溶胶）和灰霾污染的控制措施提供依据和有力的数据支持。

大气气溶胶中的超细粒子由于粒径小，扩散性强，可以直接进到人类的肺部肺泡甚至是血液内，导致比PM2.5和PM10更严重的健康危害。而且气溶胶粒子粒径越小、酸度越高，酸性的超细粒子由于具有强腐蚀性，对人体的危害更大。另外，由于很多非均相大气化学反应过程受气溶胶酸度的影响，研究大气酸性超细粒子的分布对大气化学研究显得尤为重要。因此，本项目以研究大气中酸性超细粒子的酸度和来源解析为重点，针对超细粒子（粒径<500nm）的颗粒物酸度监测方法进行搭建实验，同时通过外场试验，与目前PM2.5颗粒组分在线离线监测手段（单颗粒质谱、单颗粒黑碳、颗粒元素在线监测和滤膜多组分离线监测）相结合，分析不同地区颗粒物酸度的特征、生成机制和可能排放源，验证此检测方法数据的可靠性。研究发现，中国华北平原地区尽管SO2和硫酸盐急剧下降，但是气溶胶酸度pH依然很低，多为中等酸度。酸度粒径分布研究发现在粒径10~100nm范围内，颗粒物酸度随着粒径的变小而增加，从数浓度看酸性粒子占比最大的粒径范围在30~50nm。粒径在100~500nm范围，颗粒物酸度随着粒径的变化不大，但是随着粒径变大到800nm~1500nm范围时，酸度呈增加趋势。颗粒物的酸度粒径分布（<10µm）存在双峰双谷曲线，pH高峰值（酸度低）出现在粒径范围100nm~150nm和4µm以上，pH低值（酸度高），出现在粒径范围80nm以下和0.8~1.5µm。通过多地外场观测发现大气中酸性颗粒物的主要来源有二次转化、机动车排放、钢铁、肥料、水泥工业、燃煤和生物质燃烧排放。研究不同地区酸性粒子的污染特征和来源解析，为空气质量模式模拟（如酸沉降、二次有机气溶胶）、流行病学研究和灰霾污染控制策略提供依据和数据支撑。