研究發現：空氣污染顯著縮短壽命
A new study links heavy air pollution from coal burning to shorter lives in northern China. Researchers estimate that the half-billion people alive there in the 1990s will live an average of 5 years less than their southern counterparts because they breathed dirtier air.
China itself made the comparison possible: for decades, a now-discontinued government policy provided free coal for heating, but only in the colder north. Researchers found significant differences in both particle pollution of the air and life expectancy in the two regions, and said the results could be used to extrapolate the effects of such pollution on lifespans elsewhere in the world.
The study by researchers from China, Israel and the United States was published Tuesday in the Proceedings of the National Academy of Sciences.
While previous studies have found that pollution affects human health, “the deeper and ultimately more important question is the impact on life expectancy,” said one of the authors, Michael Greenstone, a professor of environmental economics at Massachusetts Institute of Technology.
“This study provides a unique setting to answer the life expectancy question because the (heating) policy dramatically alters pollution concentrations for people who appear to be of otherwise identical health,” Greenstone said in an email. “Further, due to the low rates of migration in China in this period, we can know people’s exposure over long time periods,” he said.
The policy gave free coal for fuel boilers to heat homes and offices to cities north of the Huai River, which divides China into north and south. It was in effect for much of the 1950-1980 period of central planning, and, though discontinued after 1980, it has left a legacy in the north of heavy coal burning, which releases particulate pollutants into the air that can harm human health. Researchers found no other government policies that treated China’s north differently from the south.
The researchers collected data for 90 cities, from 1981 to 2000, on the annual daily average concentration of total suspended particulates. In China, those are considered to be particles that are 100 micrometers or less in diameter, emitted from sources including power stations, construction sites and vehicles.
The researchers estimated the impact on life expectancies using mortality data from 1991-2000. They found that in the north, the concentration of particulates was 184 micrograms per cubic meter ― or 55 percent ― higher than in the south, and life expectancies were 5.5 years lower on average across all age ranges.
The researchers said the difference in life expectancies was almost entirely due to an increased incidence of deaths classified as cardiorespiratory ― those from causes that have previously been linked to air quality, including heart disease, stroke, lung cancer and respiratory illnesses.
Total suspended particulates include fine particulate matter called PM2.5 ― particles with diameters of no more than 2.5 micrometers. PM2.5 is of especially great health concern because it can penetrate deep into the lungs, but the researchers lacked the data to analyze those tiny particles separately.
The authors said their research can be used to estimate the effect of total suspended particulates on other countries and time periods. Their analysis suggests that every additional 100 micrograms of particulate matter per cubic meter in the atmosphere lowers life expectancy at birth by about three years.
The study also noted that there was a large difference in particulate matter between the north and south, but not in other forms of air pollution such as sulfur dioxide and nitrous oxide.
Francesca Dominici, a professor of biostatistics at Harvard School of Public Health who has researched the health effects of fine particulate matter in the U.S., said the study was “fascinating.”
China’s different treatment of north and south allowed researchers to get pollution data that would be impossible in a scientific setting.
Dominici said the quasi-experimental approach was a good approximation of a randomized experiment, “especially in this situation where a randomized experiment is not possible.”
She said she wasn’t surprised by the findings, given China’s high levels of pollution.
“In the U.S. I think it’s pretty much been accepted that even small changes in PM2.5, much, much, much smaller than what they are observing in China, are affecting life expectancy,” said Dominici, who was not involved in the study.一項新的研究表明由於燒煤引發的嚴重空氣污染將縮短中國北方居民的壽命。研究人員估計，因爲呼吸更污濁的空氣，上世紀90年代居住於北方的5億居民要比南部的居民平均少活5年。
中國可以用自身來做一個比較：幾十年來，國家政策只允許給寒冷的北方地區提供免費的煤燃料供暖，現在這項政策已經被廢止。研究人員發現，在南北兩個地區，空氣中顆粒物污染和人們的預期壽命都存在顯著差異，而且研究結果可以用來推斷在世界其他地方這種污染對壽命的影響。
這項研究由來自中國，以色列和美國的研究人員共同完成，並於週二發表在《美國國家科學院院刊》（Proceedings of the National Academy of Sciences）上。
雖然之前的研究發現，污染會影響人體健康，但是“更深層和根本上更重要的問題是對預期壽命的影響。”該項研究的作者之一，麻省理工學院環境經濟學教授邁克爾·格林斯通（Michael Greenstone）說。
“這項研究爲回答有關壽命的問題提供了一個獨特的情境，因爲（供暖）政策極大地改變了看似健康狀況相同的人生存環境的污染濃度，”格林斯通在一封電子郵件中說道，“此外，由於中國在此期間的低遷移率，我們就可以知道，人們長期以來都是暴露在一定污染濃度的環境中。”
因淮河爲中國區分南北的界限，故之前的政策爲中國淮河以北城市的家庭和辦公室提供免費的煤燃料鍋爐供暖。該政策在中央計劃的1950年-1980年期間開始實行，雖然在1980年後被廢止，但大量的煤燃燒卻給北方的空氣留下了危害人體健康的顆粒污染物。研究人員並沒有發現其他不同對待中國南北部的政策。
研究人員收集了90個城市多年總懸浮微粒日平均濃度的數據，時間跨度從1981年到2000年。在中國，懸浮微粒被認爲是指由包括髮電廠、建築工地和車輛發出的，直徑小於或等於100微米的粒子。
研究人員通過1991年-2000年的死亡率數據來估計對預期壽命的影響。他們發現，在北方，微粒的濃度爲每立方米184微克——比南部數據高55%，而且在所有年齡段的平均預期壽命比南方短5.5年。
研究人員說，預期壽命的差異幾乎完全是由於心肺死亡類疾病的發生率增加——這些通常被人們認爲是空氣質量導致的疾病包括心臟病、中風、肺癌和呼吸系統疾病。
總懸浮粒子包括被稱爲PM2.5的細顆粒物，即直徑不超過2.5微米的顆粒。因爲它可以滲透到肺部深處，PM2.5引起人們對健康的極大擔憂，但研究人員缺乏數據來單獨分析這些微小顆粒的實際影響。
該項研究的作者還說，他們的研究可以用來估計總懸浮微粒對其他國家和時段的影響。他們的分析表明，大氣中每立方米每增加100微克的顆粒物，則降低出生時3年左右的預期壽命。
該研究還指出，南北之間在顆粒物上有很大的差異，但在其他形式的空氣污染，如二氧化硫和氮氧化物上並沒有這種差異。
弗朗西斯卡·多米尼西（Francesca Dominici）認爲這項研究“有着巨大吸引力”。身爲哈佛大學公共衛生學院的生物統計學教授，多米尼西在美國研究細顆粒物對健康的影響。
中國南北方受到的不同對待使得研究人員能夠獲取到不可能在任何科學場景中得到的污染數據。
多米尼西說準實驗法是近似一個隨機實驗的很好方法，“尤其是在這種不可能做隨機實驗的情況下。”
她說，考慮到中國的高污染水平，她對調查結果並不感到驚訝。
“在美國，我想，哪怕PM2.5的數值發生很小的變化，遠遠小於他們在中國觀測到的數據，大部分人也會認爲這影響到人們的預期壽命。”並沒有參與這項研究的多米尼西說道。
