The International Agency for Research on Cancer (IARC) has classified ambient outdoor particulate matter (PM) as a Group 1 human carcinogen. It is unclear, however, if the lung cancer risks primarily linked to long-term exposure to fine PM (PM2.5, aerodynamic diameter <2.5µm) are driven, in part, by its constituent ultrafine particles (UFP, <100nm), which have great potential for biological effects due to their small size. This prospective cohort study among the NIH-AARP Diet and Health Study participants in the Los Angeles Basin is being conducted in collaboration with the University of Southern California and Utrecht University. Its primary aim is to evaluate the association between long-term exposure to ambient outdoor ultrafine particulate matter and lung cancer risk.
The study population has several important features needed to assess the etiologic relationship between ambient outdoor UFP exposure and lung cancer risk, including substantial regional variation in PM concentrations, large numbers of lung cancer cases, and data on smoking and residential histories. A comprehensive retrospective exposure assessment draws upon one of the most complete repositories of historical UFP data available, supplemented by a mobile ambient monitoring campaign in Los Angeles.