Friday, November 9, 2018 - 12:00pm
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100F Pierce Hall, 29 Oxford St., Cambridge

Atmospheric & Environmental Chemistry Seminar

Professor Dan Jaffe, University of Washington, will discuss "Fires, Smoke, and Urban Air Quality in the Western U.S."

In the past two decades, the area of wildland fires has approximately doubled from what it was in the preceding two decades, with most of that increase occurring in the Western U.S.   This has given rise to many days in the west with the worst air quality every measured in America. As a result of research on air quality impacts from smoke over the past few years we have made great progress in understanding some key aspects of the atmospheric chemistry.   For example:

Over the last 3 decades PM2.5 has increased at the 98th percentile due to wildfires over a large portion of the western U.S. (McClure and Jaffe 2018, PNAS).

Analysis of a large number of smoke events from 18 monitoring locations in the Western  U.S. shows that average O3production rates are enhanced by ~1-2 ppb/hour during the daytime, compared to non-smoke days.   This is due to a large enhancement from VOCs and a smaller enhancement from NOx. During days with smoke influence, maximum daily 8-hour averaged O3 (MDA8) generally increases with the daily mean PM2.5 with an average slope of ~0.5-1 ppb per ug/m3 up to approximately 60 ug/m3, but with a large degree of variability.   Above this level, O3 production appears to be suppressed, most likely due to photolysis effects.

Because O3 is difficult to predict from Eulerian photochemical models, we have developed a statistical approach using Generalized Additive Modeling (GAM) that can be used to estimate the smoke influence on O3.    This approach shows that fire emissions can result in enhancements in the O3 max daily 8-hour average (MDA8) of up to 30 ppb, but again with a large degree of variability.   The GAMs also show that the strongest influence from fires is on photochemically active days, with much lower influence on other days.

The question of climate change influence on the increasing area burned is complex.  The general pattern of forests in America has changed dramatically over the past 100 years due to fire suppression, while average and extreme temperatures have increased, as has lightning.  Throw in the effects from human ignitions, predators like Pine Bark Beetle and Spruce Bark Beetle, which damage forests and leave them more susceptible to fires, and the problem gets even more complex.  Given the millions of people that were exposed to very unhealthy air quality over the past few years, and the many more who will be exposed in the future, it is important to review our advice for reducing personal exposure.  Based on my observations and data in 2018, this advice needs significant rethinking.

Contact Name: 

Kelvin Bates

Research Areas: 

Harvard University
Center for the Environment

Address: 26 Oxford Street, 4th Floor, Cambridge
Phone: (617) 495-0368

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