The effects of wildfire atmospheric emissions on
regional air quality using current and future
climate simulations
Ivy
1
1
Tao ,
Rodrigo
Bryn Mawr College
Introduction
Wildfires are a source of emissions for many chemical species
into the atmosphere. These species either directly affect the air
quality or produce secondary
pollutants such as ozone (O3)
and particulate matter (PM).
The dispersion and chemical
processing of wildfire
emissions are affected by
meteorological conditions. As
part of an ensemble study of
the impact of climate change
on regional air quality in the
US, the goal of this project is
to investigate the effects of
Figure 1. California Malibu area wildfire
wildfire emissions on air
captured by NASA’S Terra satellite, at
quality.
1
2:25p.m EST on October 23, 2007
Methodology
• Wildfire emissions for 1996 and 2048 summers (June, July,
August) were analyzed. These are the warmest years in the
decades 1995-2004 and 2045-2054, respectively, of the ECHAM5
global climate model results.
• Impact of wildfire emissions on air quality is modeled using the
WRF-SMOKE-CMAQ modeling framework:
 Meteorological fields were downscaled from the ECHAM5
global climate model to the 36-km US domain using the WRF
v2.22 mesoscale meteorological model;
 Wildfire emissions were obtain from the historical burn records;
 Biogenic emissions were estimated with the Model of
Emissions of Gases and Aerosols from Nature (MEGAN)3;
 Anthropogenic emissions were obtained from the 2002
National Emissions Inventory (NEI)4; and
 Concentrations of ozone and PM2.5 (PM with aerodynamic
diameter less than 2.5 m) were calculated using the chemical
transport model CMAQ5.
• Three simulations were performed to evaluate the impact of
wildfire emissions on air quality:
1) Current (1996) meteorology was used to calculate plume rise
and dispersion of historical records of wildfires;
2) Future (2048) meteorology was used to calculate plume rise
and dispersion of historical records of wildfires; and
3) The current case was re-run with wildfire emissions removed
(Zero fire case).
• Results were analyzed for the Northwest, Southwest and Central
regions of the US where wildfires were most significant.
Figure 2. US divided into seven
regions. Central (deep blue),
Northwest (tan), and Southwest
(yellow) are the focus of this study
2
2
Gonzalez-Abraham ,
Serena H.
2
Chung ,
Brian K.
2
Lamb
Laboratory of Atmospheric Research, Washington State University
Wildfire Contribution to Emissions
Daily 8-hr averaged O3 Concentration Differences
Figure 7: Difference maps of daily 8-hr averaged O3 concentrations between the 1996 historical fire case and the
1996 zero fire case. From left to right, Northwest, Southwest, Central
Figure 4. Percentages and the amounts of pollutants emitted by wildfires
by region. The species are nitrogen oxides (NOx), carbon monoxide (CO),
volatile organic compounds (VOCs), ammonia (NH3), PM2.5, sulfur
dioxide (SO2), methane (CH4), elemental carbon (PEC), fine particulate
matter (PMfine), particulate nitrate (PNO3), primary sulfate (PSO4), sulfur
(SULF), and primary organic aerosol (POA).
Whisker plots of Air Quality Indicators from CMAQ
Figure 8: Same as above, but for 2048 case minus 1996 historical fire case.
The difference maps for the 1996 zero fire case and historical fire case show little change in O 3
concentrations. For the comparison of the 2048 simulation and historical fire case, we can see that
meteorology has a significant effect on O3 concentrations.
Averaged Hourly PM2.5 Concentration Differences
Figure 9: Difference maps of averaged PM2.5 concentrations between the 1996 historical fire case and the 1996 zero
fire case. From left to right, Northwest, Southwest, Central.
Figure 5. Ozone daily 8-hr average (up left) and PM2.5 (up right) concentration distributions.
For ozone, the three cases show little difference in concentration distributions for the regions
Northwest and Southwest. For Central, the zero fire case concentrations are less than 1%
lower than the fire case, and the 2048 simulation concentrations increase about 1-2% with
respect to 1996 fire case. This is also observed for PM2.5 in the Northwest and Southwest.
However, for Central, there is little variation between the zero fire case and the fire case, but
a significant decrease in concentrations between the 2048 simulation and the 1996 fire case.
Figure 10: Same as above, but for 2048 case minus 1996 historical fire case.
Several peaks are observed in both sets of comparison. Most peaks are located in forests and mountains
while others locate in urban areas or high ways. For the difference maps between the 1996 zero fire case
and the fire case, no significant increase is seen in the areas several grid cells away from the peak grid
cells. For the difference maps between the 2048 simulation and the 1996 fire case, the peaks all represent
large decrease in PM2.5 concentrations. However, the coastal areas experience a rise of 0.5-3 g/m3 in
concentrations.
1996 vs 2048 Summer Meteorology
Surface Temperature (oC)
Insulation (W/m2)
Conclusion and Future Work
Wind Speed (m/s)
Boundary Layer Height (m)
Figure 6. CO (left) and NOx (right) concentration distributions.
Water Vapor (kg/kg)
Precipitation (cm)
Figure 3. Meteorological conditions for summer 1996 and 2048.
For CO and NOx, the three cases show no differences in concentration distributions for the
Northwest and Southwest. For CO in Central, there is less than 1% increase for the 1996 fire
case compared to the zero fire case. The 2048 simulation decreases slightly compared to the
1996 fire case. The NOX distribution in the Central region in the zero fire case decreases at
higher concentrations.
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http://www.nasa.gov/vision/earth/lookingatearth/socal_wildfires_oct07.html
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advanced Research WRF Version 2. NCAR Tech Note, NCAR/TN-468+STR, 88pp.
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emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature), Atmos. Chem. Phys. Discuss., 6, 10
107-173, doi:10.5194/acpd-6-107-2006, 2006
4. US Environmental Protection Agency. “2002 National Emissions Inventory Data and Documentation.” Access on 1 August
2010 http://www.epa.gov/ttn/chief/net/2002inventory.html#documentation
• Emissions of wildfires do not affect atmospheric concentrations of O 3 significantly as they do on those of
PM2.5. This is because fires themselves release large amounts of PM directly, and O 3 is only a secondary
pollutant.
• The comparisons between the 2048 simulation and 1996 historical fire case indicate that climate has a
significant impact on PM2.5. The most obvious change in meteorology for 2048 is the increase in
precipitation, which leads to a decrease in PM2.5 concentrations near the source locations, for precipitation
removes particles in the air. It is uncertain what causes the increase in PM2.5 concentrations in other
regions.
• The rise in ozone concentrations may be due to the increased temperatures. More analysis is needed to
explain the diverse patterns seen in the ozone concentration difference maps.
• Future work will included extending the simulations to more years and analyzing the impact of wildfire
emissions in the context of other global change variables.
Acknowledgement: This work is supported by the National Science Foundation Research Experience for
Undergraduates grant (ATM-0754990) and Bryn Mawr College HHMI Science Horizon Scholarships.
5. DW Byun, JKS Ching,1999: Science algorithms of the EPA Models-3 community multiscale air quality (CMAQ) modeling system. Rep.
EPA/600/R-99.
R Development Core Team (2008). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna,
Austria. ISBN 3-900051-07-0, URL http://www.R-project.org.
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and PM2.5 concentrations to global changes, Atmos. Chem. Phys. 9, 2009.
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effects of global changes upon regional ozone pollution in the United States, Atmos. Chem. Phys. 9, 2009.