Levels of Outdoor PM2.5 and Absorbance as Surrogates for Personal Exposures Among Post-Myocardial Infarction Patients

Abstract

TAA3-O-02 Introduction: Outdoor levels of fine particles (PM2.5; particles <2.5 μm) have been associated with cardiovascular health in epidemiologic studies. Persons with existing cardiovascular disease have been suggested to be especially vulnerable. The use of outdoor concentrations to estimate personal exposures has been questioned in this population group due to their less active lifestyle. The objective of the study was to assess the relationship between outdoor and personal PM2.5 and absorbance, indicator for combustion originating PM2.5, among subjects with cardiovascular disease. Methods: The study was conducted in a Mediterranean city between November 2003 and June 2004 within a larger epidemiologic study. Post-myocardial infarction patients visited a clinic for health examination every 4th week. They carried personal PM2.5 monitors for 24 hours before every visit. At the same time, PM2.5 was measured at a fixed outdoor monitoring site. Absorbance of all PM2.5 filter samples was measured as a marker for elemental carbon. Results: There were 36 patients (83% males, average age 61 years) with 2 to 6 measurements, and 105 valid samples. Levels of outdoor PM2.5 (median = 16.97 μg/m3) were lower than personal concentrations (median 34.1 μg/m3), even after excluding days with exposure to environmental tobacco smoke (ETS) (n = 44, median after exclusion 28.2 μg/m3). However, outdoor absorbance (median 4 m−1/105) was similar to personal absorbance (median 2.9 m−1/105) after exclusion of ETS. Outdoor and personal PM2.5 were not correlated cross-sectionally, whereas outdoor absorbance was correlated with exposure (r = 0.41), especially after excluding days with ETS (r = 0.77). In mixed models, where the repetitive nature of the measurements was taken into account, there was a statistically significant association between personal and outdoor absorbance when adjusting for ETS (slope 0.72, P < 0.001), but for PM2.5 the association was weaker (slope 0.57, P = 0.074). Discussion and Conclusions: Outdoor measurements of PM2.5 absorbance, a proxy for combustion originating fraction of PM2.5, estimate well both the variation and levels of personal exposure when exposure to ETS has been taken into account. For PM2.5 there are more indoor and personal sources to consider.