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The relationship of high PM2.5 days and subsequent asthma-related hospital encounters during the fireplace season in Phoenix, AZ, 2008–2012


Exposure to particulate matter less than 2.5 μm in diameter (PM2.5) exacerbates asthma and increases mortality. In Phoenix, AZ, the highest PM2.5 values frequently occur during the winter fireplace season and air quality health standards are often exceeded during the Christmas and New Year’s holidays. It was clear that enhanced messaging was needed by air quality and public health authorities to discourage biomass fires (BMF) on days when unhealthful levels of pollution were likely to be caused by that activity. Demonstrating adverse health outcomes would bolster this effort. We conducted this study to evaluate associations between elevated PM2.5 exposures during the fireplace season and asthma-related hospital admissions in Phoenix; days with average PM2.5 > 35 μg/m3 were categorized as elevated PM2.5 exposure. We used hospital discharge data to identify patients with an asthma-related hospital encounter and who lived within an 8-km radius of a PM2.5 monitor. To estimate the risk of a hospital encounter following an elevated PM2.5 event, we used generalized estimating equations, specified with a Poisson distribution, and exposure lags of 0–3 days. Controlling for influenza, temperature, humidity, rain, and year, these analyses generated elevated estimates of emergency department visit risk among adults on lag days 2 (relative risk [RR] 1.19; 95 % CI 1.06, 1.34) and 3 (RR 1.20, 95 % CI 1.05, 1.37). Elevated PM2.5 was not associated with hospital encounters among children. Our findings suggest that adults may be at elevated risk of asthma-related hospital encounters during the fireplace season.

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Fig. 1


  1. 1.

    Arizona Revised Statutes §§9–500.16 and 11–875 requires all homes in the Phoenix air pollution control area built after 1998 to comply with clean-burning fireplace standards, e.g., EPA-certified permanently installed gas or electric log inserts.


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The authors wish to thank Ahmed Mohamed and Kate Goodin of the Maricopa County Public Health Department for their research assistance. The authors also thank the internal reviewers at the Centers for Disease Control and Prevention for their helpful suggestions. Finally, they thank the anonymous external reviewers for their comments on the article.

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Correspondence to Ronald Pope.

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The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention.


This study was funded as a joint operation between the Maricopa County Air Quality Department, the Maricopa County Department of Public Health, and the Centers for Disease Control and Prevention. No outside grant funding was received.

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The authors declare that they have no conflict of interest.

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Pope, R., Stanley, K.M., Domsky, I. et al. The relationship of high PM2.5 days and subsequent asthma-related hospital encounters during the fireplace season in Phoenix, AZ, 2008–2012. Air Qual Atmos Health 10, 161–169 (2017).

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  • Air pollution
  • Air quality
  • Asthma
  • Biomass burning
  • Epidemiology
  • Respiratory health