Using National Ambient Air Quality Standards for fine particulate matter to assess regional wildland fire smoke and air quality management.

Wildland fire is an important ecological process in the California Sierra Nevada. Personal accounts from pre-20th century describe a much smokier environment than present day. The policy of suppression beginning in the early 20th century and climate change are contributing to increased megafires. We use a single particulate monitoring site at the wildland urban interface to explore impacts from prescribed, managed, and full suppression wildland fires from 2006 to 2015 producing a contextual assessment of smoke impacts over time at the landscape level. Prescribed fire had little effect on local fine particulate matter (PM2.5 ) air quality with readings typical of similar non-fire times; hourly and daily good to moderate Air Quality Index (AQI) for PM2.5 , maximum hourly concentrations 21-103 μg m-3 , and mean concentrations between 7.7 and 13.2 μg m-3 . Hourly and daily AQI was typically good or moderate during managed fires with 3 h and one day reaching unhealthy while the site remained below National Ambient Air Quality Standards (NAAQS), with maximum hourly concentrations 27-244 μg m-3 , and mean concentrations 6.7-11.7 μg m-3 . The large high intensity fire in this area created the highest short term impacts (AQI unhealthy for 4 h and very unhealthy for 1 h), 11 unhealthy for sensitive days, and produced the only annual value (43.9 μg m-3 ) over the NAAQS 98th percentile for PM2.5 (35 μg m-3 ). Pinehurst remained below the federal standards for PM2.5 when wildland fire in the local area was managed to 7800 ha (8-22% of the historic burn area). Considering air quality impacts from smoke using the NAAQS at a landscape level over time can give land and air managers a metric for broader evaluation of smoke impacts particularly when assessing ecologically beneficial fire. Allowing managers to control the amount and timing of individual wildland fire emissions can help lessen large smoke impacts to public health from a megafire.