近二十多年來，由於科技突飛猛晉與高度工業化，導致經濟快速成長，民眾生活條件更加富裕與便利，但也帶來一些負面效應，如空氣污染(air pollution)、地球暖化，主要是由於石化燃料、工業排放、移動源廢氣(exhaust gas)等燃燒行為。長期暴露大量空氣懸浮微粒(particulate matter,PM)，如二氧化硫(SO2)、二氧化氮(NO2)、懸浮微粒、臭氧(ozone)等，會產生負面健康效應，罹病率和死亡率風險大為提升；有研究報告指出即使是短期暴露細懸浮微粒PM2.5(微粒直徑小於2.5微米)，也會增加罹患心血管疾病和死亡風險。尤其是以人口密集及機動車輛眾多(機車、轎車、計程車、公共汽車、卡車、貨車等)之大都會區，如台南市、高雄市、北京、上海等城市，天空經常是灰暗與充滿霧霾。西元1952年12月5日至8日，大量濃霧覆蓋整個倫敦，持續好幾天，霧主要成份是懸浮微粒與二氧化硫(源自家用煤炭燃燒)，急性大量暴露結果，此段期間死亡人數急速上升，尤其本身已罹患慢性呼吸道疾病或心臟疾病者，約60%-70%為60歲以上長者，另外1歲以下嬰幼兒死亡率亦倍增，促使英國政府於西元1956年立法通過「清淨空氣法案」(Clean Air Act)，限制家庭用煤炭之燃燒使用[1]。
國際癌症研究中心(International Agency for Research on Cancer,IARC)，從已發表文獻之充分證據，將PM2.5列為人類一級致癌物(carcinogen)，和暴露石綿、砷化物、苯、游離輻射、焦油、氡、鐳、鉻、鎘、氯乙烯等致癌物並列，藉以喚起社會大眾及國家環境保護機構之重視。美國是最早提出PM2.5空氣品質標準及相關管制規範的國家，早在西元1980年開始陸續進行PM2.5各項基礎研究，歷經背景調查分析及建置工作，遂在西元1997年首次提出PM2.5空氣品質標準，經過多次討論修正，於西元2012年將空氣品質標準修訂為12 ug/m3，取代既有之空氣污染指標(Pollutant Standard Index,PSI)[2]。重要空氣污染物(air pollutants)包括二氧化碳、二硫化碳、氧化氮及微量重金屬等，雖有些污染物會引發立即性效應，但大多數污染物需一段長間累積在身體內而導致傷害。空氣污染來源可分為自然界產出及人類行為產出，前者如火山爆發、岩床氡氣釋放、沙塵暴、龍捲風等；人為污染如汽機車廢氣、工廠排放、石化燃料、核彈試爆、燃燒稻草、隧道橋樑工程爆破、煤礦開採、焚化爐等。

For recent decades,due to highly techonological innovation and industrialization, it had fasteconomic growth, and life conditions promoted to be wealthier and more convenient.On the contrary,these may produce some negative effects,such as air poll-ution,global warming etc.,mainlydue to fossil fuels,industrial emissions,and mobile vehicles exhaust gas.Long-term exposed tolarge amount particulate matters,such as ozone,nitrogen dioxide,sulfur dioxide,etc.,they may producesome negative health effects,and increase risks of morbidity and mortality.Some researchespointed out that even short-term exposure of fine particulate matter PM2.5,might increase risks ofcardiovascular morbidity and death,especially for the elderly,infants,COPDs,CAD, asthma,etc.Forexample,a dense fog covered the Greater London area during 5-8 Dec -cember 1952.During thistime there was a sudden and enormous rise in mortality, which far exceeded anything previouslyrecorded in a similar period of fog.This fog instigated the Clean Air Act 1956.A major influence ofthis act was a restriction in the burning of domestic coal fires.
International agency for research on cancer(IARC) strongly suggested that PM2.5 is group 1human carcinogen,derived from epidemiological evidence reports.U.S.A. is the first country,whoset up air quality standard of PM2.5 and related regulations. In 2012,U.S.A. revised the air qualitystandard to 12 ug/m3,to replace the former PSI (Pollutant Standard Index).Though some pollutantshave immediate effects,but many take a longer time to accumulate in the body and causeharm.Based on epidemiolo-gic evidences,it is generally accepted that PM2.5 is more toxic andharmful for health than PM10,because PM2.5 can be inhaled more deeply into the lungs and offera greater surface,hence potentially larger concentrations of toxic air pollutants per unit mass.