麻省理工學院（MIT）航太與環境實驗室研究指出，經追蹤工業煙囪、車輛排氣管、船隻和鐵路運輸以及住商暖氣的排放氣體後發現，空氣汙染每年大約造成全美20萬人早逝。
死因為空氣污染相關者的死亡年齡多半會提早十年，其中以道路運輸排放的氣體最為致命，每年造成53,000人提早死亡；緊接著是發電廠，每年造成52,000人提早死亡。
主要研究者，也是MIT的航太系助理教授Steven Barrett指出，「過去5到10年間，空氣汙染和早期死亡間的關係已累積許多科學證據和政治關注。空氣汙染是所有城市的共通問題，極待解決。」
研究團隊從美國環保署的國家排放清冊中蒐集2005年的數據。2005年是研究執行時所能取得的最新資料。雖然資料僅反映2005年的排放情況，Barrett表示，研究結果仍反映今日空氣汙染相關的健康風險。
Barrett的研究團隊將原始資料依汙染來源分成六組：發電、工業、住商、道路運輸、海洋運輸和鐵路運輸。將六組排放數據輸入模擬大氣中粒子與氣體排放效應的空氣品質模型。為決定何種排放的影響最大，研究團隊將各種排放組別分別從模擬中移除，觀察污染物的濃度變化。
研究人員分析5,695個美國城市的空氣汙染排放狀況，發現加州的空汙問題最嚴重，每年造成21,000人提早死亡，主要空汙來源是道路運輸和住商暖氣及烹飪排放的氣體；而巴爾的摩的空氣汙染相關致死率最高，每年每100,000個居民中就有130個可能死於長期暴露於空氣汙染之中。
當被問及為什麼陸地運輸造成53,000人提早死亡，而發電廠僅52,000人，研究者解釋，「交通工具大多在人口密集的地區移動，增加大量人口所接觸的汙染物，而發電廠大多位於偏遠地區，且排放氣體多往高緯度地區飄移。」
波士頓大學環境衛生學系教授Jonathan Levy說，Barrett的研究結果和美國環保署的結論相符合。「此類大規模的公共衛生問題需要透過政策面來改善，現在的科技已經進步到足以應付這些問題。」Levy說。
接著研究團隊將模擬所得數據和美國的人口密度地圖進行比對，以了解各地區人口最容易暴露何種汙染來源。
中西部的工業空氣汙染最嚴重，尤其在芝加哥到底特律之間。費城、亞特蘭大和洛杉磯等城市也有高度的工業空氣汙染。在中部東邊和中西部，發電廠造成的空氣汙染對早期死亡的影響最為嚴重，因為東部電廠使用的煤硫含量遠較西部電廠高。
暖氣和烹飪排放氣體等住商空氣汙染造成的早期死亡多發生在美國東西沿岸人口密集的地區。墨西哥灣沿岸地區的工業空氣汙染情形也不容小覷，因為美國最大的煉油廠皆集中在此。運輸和港口空氣汙染情形最嚴重的地區是南加州，每年造成3,500人提早死亡。鐵路運輸空氣汙染相關的提早死亡情況相對輕微，且一致地集中在美國中部東邊和中西部。
Polluted air causes roughly 200,000 early deaths each year across the United States, researchers from the Massachusetts Institute of Technology conclude after tracking emissions from industrial smokestacks, vehicle tailpipes, marine and rail transport, and commercial and residential heating.
Emissions from road transportation are the most deadly, causing 53,000 premature deaths a year, followed by power generation, with 52,000 deaths, finds the study by MIT’s Laboratory for Aviation and the Environment.
Lead researcher Steven Barrett, an assistant professor of aeronautics and astronautics at MIT, said that a person who dies from an air pollution-related cause typically dies about a decade earlier than he or she otherwise might have.
“In the past five to 10 years, the evidence linking air-pollution exposure to risk of early death has really solidified and gained scientific and political traction. “There’s a realization that air pollution is a major problem in any city, and there’s a desire to do something about it,” Barrett said.
California suffers the worst health impacts from air pollution, with about 21,000 early deaths annually, mostly attributed to road transportation and to commercial and residential emissions from heating and cooking, the researchers learned from their state-by-state analysis.
Of the 5,695 U.S. cities where the scientists mapped local emissions, they found the highest emissions-related mortality rate in Baltimore, where 130 out of every 100,000 residents is likely die in a given year due to long-term exposure to air pollution.
The team based its research on emissions data from the U.S. Environmental Protection Agency’s National Emissions Inventory, a catalog of emissions sources nationwide. The researchers collected data from the year 2005, the most recent data available at the time of the study.
While the data reflects conditions in 2005, Barrett says the results likely represent today’s pollution-related health risks.
Barrett’s team divided the raw data into six emissions sectors: electric power generation; industry; commercial and residential sources; road transportation; marine transportation; and rail transportation.
They fed the emissions data from all six sources into an air-quality simulation of the impact of emissions on particles and gases in the atmosphere.
To determine where emissions had the greatest impact, they removed each sector of interest from the simulation and observed the difference in pollutant concentrations.
The team then overlaid the resulting pollutant data on population-density maps of the United States to see which populations were most exposed to pollution from each source.
To explain why 53,000 early deaths a year were attributed to car and truck exhaust while only 52,000 premature deaths annually were blamed on power plants, the researchers reasoned that “vehicles tend to travel in populated areas, increasing large populations’ pollution exposure, whereas power plants are generally located far from most populations and their emissions are deposited at a higher altitude.”
Pollution from electricity generation had the greatest impact on premature death in the east-central United States and in the Midwest because Eastern power plants tend to use coal with higher sulfur content than Western plants, the researchers said.
Most premature deaths due to commercial and residential pollution sources, such as heating and cooking emissions, occurred in densely populated regions along the East and West coasts.
Pollution from industrial activities was highest in the Midwest, roughly between Chicago and Detroit, as well as around Philadelphia, Atlanta and Los Angeles.
Industrial emissions also peaked along the Gulf Coast region because the largest oil refineries in the United States are located there.
Southern California saw the largest health impact from shipping and port activities, with 3,500 related early deaths a year.
Emissions-related deaths from rail activities were comparatively slight, and spread uniformly across the east-central part of the country and the Midwest.
Jonathan Levy, a professor of environmental health at Boston University who was not involved in the research, says Barrett’s calculations for the overall number of premature deaths related to combustion emissions agree with similar conclusions by the Environmental Protection Agency.
“A public-health burden of this magnitude clearly requires significant policy attention, especially since technologies are readily available to address a significant fraction of these emissions.” said Levy.
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