Wildfires Send Ozone Pollution Soaring

Wildfires Send Ozone Pollution Soaring



October 2008  - Wildfires can hike ozone 
pollution to levels that violate U.S. public health and environmental 
standards, new research has determined. 
The study by scientists at the National Center for Atmospheric Research 
focused on California wildfires in 2007, finding that they repeatedly 
caused ground-level ozone to spike to unhealthy levels across a broad 
area, including much of rural California as well as neighboring Nevada. 
Fires worsen ozone levels by releasing nitrogen oxides and hydrocarbons, 
which can form ozone near the fire or far downwind as a result of chemical 
reactions in sunlight. 
The study was published today in "Geophysical Research Letters." It was 
funded by NASA and by the National Science Foundation, which sponsors 
NCAR. 

"It's important to understand the health impacts of wildfires," says NCAR 
scientist Gabriele Pfister, the lead author. "Ozone can hit unhealthy 
levels even in places where people don't see smoke." 
Although scientists have long known that wildfires can affect air quality 
by emitting particles and gases into the air, there has been little 
research to quantify the impacts. 
The researchers, using a combination of computer models and ground-level 
measurements, studied intense California wildfires that broke out in 
September and October of 2007. They found that ozone was three times more 
likely to violate safe levels when fire plumes blew into a region than 
when no plumes were present. 
At the time of the wildfires, the public health standard for ozone set by 
the U.S. Environmental Protection Agency was 0.08 parts per million over 
an eight-hour period. 
The EPA has since tightened the standard to 0.075 parts per million. Under 
the stricter standard, the number of violations would have nearly doubled. 

While ozone in the stratosphere benefits life on Earth by blocking 
ultraviolet radiation from the Sun, ozone in the lower atmosphere can 
trigger health problems. 
These range from coughing and throat irritation to more serious problems, 
such as aggravation of asthma, bronchitis, and emphysema. Ground-level 
ozone pollution also damages crops and other plants. 
"Wildfires are expected to worsen in the future, especially as our climate 
grows warmer," Pfister says. "But we are only now beginning to understand 
their potential impacts on people and ecosystems, not only nearby but also 
potentially far downwind." 
The unhealthy levels of ozone the researchers detected occurred mostly in 
rural areas. This finding may be a result of the computer modeling, which 
lacked the fine detail to zoom in on relatively compact urban areas. 
But the authors also speculate that wildfire emissions have a greater 
impact on ozone levels in the countryside than on cities. 
They say cities tend to have more nitrogen dioxide, a pollutant that can, 
at high levels, reduce the efficiency with which ozone is produced or even 
destroy ozone. 
"The impact of wildfires on ozone in suburban and rural areas, far from 
urban sources of pollution, was quite noticeable," says NCAR scientist 
Christine Wiedinmyer, a co-author of the paper. 
The paper notes that ozone levels would likely have been even greater 
except that Santa Ana winds in October blew wildfire plumes over the 
Pacific Ocean, safely away from populated areas. 
To measure the impact of the fires on ozone formation, the researchers 
used a pair of computer models developed at the National Center for 
Atmospheric Research. 
With the first one, a specialized fire model, they estimated the amount of 
vegetation burned and resulting emissions of nitrous oxides, sulfur 
dioxide, and other pollutants. 
Those results went into a global air chemistry model that simulated the 
movement of the emissions and tracked the resulting formation of ozone as 
the fire plumes spread downwind. 
The scientists verified the accuracy of their modeling results by 
comparing them with ozone measurements from a network of EPA ground 
stations at various sites in California. 
This also allowed them to determine both the number of ozone violations 
and the extent to which the wildfires contributed to those violations.





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