Influence of Wildfires on Surface Ozone in Colorado

Transcription

1 Influence of Wildfires on Surface Ozone in Colorado Author: So-Yun Kim Affiliation: Student, Fairview High School, Boulder, CO Author Contact Information: Phone:

2 Abstract Surface ozone is harmful to human health; ozone is known to aggravate human lungs, which can be extremely harmful towards people with asthmatic conditions. Tropospheric ozone is formed from nitrogen oxides and volatile organic compounds that are emissions from anthropogenic activities and natural phenomena such as wild fires. This study examines the extent to which wildfires affect surface ozone in Colorado. Using surface ozone observations and NASA MODIS fire count and area burnt data, the events of high Colorado ozone (8 hour average ozone above 75 ppbv) in summer of 2012 were identified for the period of record-breaking wildfires in Colorado. First, a high ozone episode on July 4 th, 2012 was focused. The NASA MODIS images discovered that there were multiple local and distant fires influencing Colorado air quality on the 4th. Further trajectory model analysis demonstrated that the plumes from the Waldo Canyon fire, Colorado Springs and a Wyoming fire were carrying around ozone precursors within Colorado. A high ratio of carbon monoxide to carbon dioxide at the time of high ozone measured at NOAA Boulder Atmospheric Observatory was conclusive that the wildfires contributed to the increase of surface ozone in Colorado Front Range region on the 4th. Second, multi-year analysis was performed. It also revealed that there was a significant visible correlation between high ozone events and the areas burnt by fire in the Western U.S. For example, year 2007 and 2012 have the highest average ozone levels and number of violations, corresponding to the fact that year 2007 and 2012 have the greatest area burnt across the Western U.S. The correlation of surface ozone in Colorado with in-state area burnt was less certain. This study indicates that the wildfires across the Western U.S. can increase the surface ozone in Colorado. 2

3 Table of Contents Introduction.. 4 Methods Results.. 8 Conclusion 16 Reference

4 1. Introduction Tropospheric ozone (O3) is formed from chemical reactions involving nitrogen oxides, NOX (=NO+ NO2), and volatile organic compounds (VOC) under sunlight (Jaffe and Wigder, 2012). NOx and VOC emissions mainly originate from combustions of fossil fuels. High ozone levels frequently occur during the summertime under high-pressure systems near urban and industrial regions. Elevated levels of surface ozone can be hazardous to human health and vegetation. For example ozone is known to irritate lungs, aggravate bronchitis, and worsen asthma (Lippmann, 1991; McConnell et al., 2002; Bell et al., 2004; Kim et al., 2011). Therefore the EPA (U.S Environmental Protection Agency) has set an air quality standard for ozone levels at 75 parts per billion by volume (ppbv) for an 8-hour average, and it is evaluated using the 3-year running average of the fourth highest annual ozone value. ( A contributor to surface ozone is wildfires. Wildfires emit a large amount of ozone precursors (NOx and VOC), green house gases (CO2, CH4, and N2O), and aerosols (Crutzen and Andreae, 1990; Andreae and Merlet, 2001; Wiedinmyer et al., 2006). Many studies suggest ozone production as a result of wildfires (Pfister et al.,2008; Jaffe and Wigder, 2012 and references therein). Ozone from wildfires is determined by complicated interplay of emissions, chemical reactions, and transport by winds. Ozone can travel or be chemically produced long distances away from the active fire regions (Wotawa and Trainer, 2000). In the intense local plumes of wildfires, ozone may not be enhanced because of the nonlinear ozone chemistry (Jaffe and Wigder, 2012). Gillet et al. (2004) and Westerling et al. (2006) have shown that global warming has caused an increase in frequency, duration, and 4

5 intensity of wildfires in the U.S. and Canadian forests. Jaffe et al. (2008) exhibited inter annual variation in the western U.S. ozone is significantly correlated with the area burned by wildfires: the average and maximum ozone at rural sites (e.g., U.S. National Parks) was enhanced due to the wildfires. The wildfires in Colorado have set historical records over the past years. The Fourmile Canyon fire occurred during September 6-16, 2010 near Boulder, Colorado and burned 2500 acres of montane forest and destroyed 169 homes (Stone et al., 2011). Many wildfires occurred in 2012 potentially under the condition of record high temperatures (101 F). For example the High Park fire in Fort Collins (June 9-30) was the second largest fire in recorded Colorado history by burned area. The Waldo Canyon fire in Colorado Springs (June 23-July 10) was the most expensive fire in Colorado history; 364 homes were burned. The objective of this study is to understand the influence of the wildfires on Colorado s surface ozone because of the possible health impacts. This study is guided by the idea that photochemistry enhances ozone production and predicts that the average or maximum level of surface ozone in rural and urban Colorado is positively correlated with the number of fires or burned areas. As mentioned above, ozone is difficult to predict because of the complicated interactions between chemistry and transport. Although the concept seems simple, the ozone production from wildfires is still not well understood and quantified through intensive observations. The study period is from 2007 to This time period is to be investigated because of the decreasing anthropogenic emissions from automobile sources (Bishop and Stedman, 2008; Russell et al., 2012), in contrast to the increasing number of wildfires in the western U.S., in particular, Colorado. Most of 5

6 the studies on wildfires and ozone examine remote and rural areas, relatively far from urban areas due to the difficulty in differentiating between anthropogenic and wildfire emissions. Due to the decreased anthropogenic emissions and prolonged and intensive wildfires near urban areas in Colorado (e.g., Fort Collins, Boulder, Denver, and Colorado Springs) it is possible to examine the influence of wildfires in urban and rural areas. 2. Methods 2.1. Data Collection Publically available data sets from various government agencies are collected. Fire emissions data (FINNv1) The Fire INventory from National Center for Atmospheric Research version 1.0 (FINNv1, web-link: bai.acd.ucar.edu/data/fire/) provides daily, 1 km spatial resolution, global estimates of the trace gas and particle emissions from wildfires (Wiedinmyer et al., 2011). FINN includes Julian day, time, vegetation type, latitude, longitude, area burnt (m 2 ), and trace gases (mol/hour) such as CO2, CO, NOX, SO2, NH3, CH4, and VOCs. The location and time of the fires are identified by MODIS (Moderate Resolution Imaging Spectroradiometer) instrument measurement onboard the NASA (National Aeronautics and Space Administration) Terra and Aqua polar-orbiting satellite (Giglio et al., 2006). EPA and National Park Service There are 60 to 70 ozone-monitoring sites in Colorado during At 34 sites, ozone was measured consistently through The locations of the sites range from urban to rural regions including National Parks such as the Rocky Mountain National Park and Mesa Verde National Park. Data measured hourly will 6

7 be used. The data can be downloaded from and www2.nature.nps.gov/air/monitering/network.cfm. Air temperature measured at the monitoring sites was also used. Boulder Atmospheric Observatory (BAO) tower The BAO tower is a research facility located in Eerie, Colorado maintained by NOAA (National Oceanic and Atmospheric Administration). The types of data measured 10 meters from the ground are wind, temperature, relative humidity, ozone, carbon monoxide (CO), and CO2. At 100 and 300 m levels, CO and CO2 along with other meteorological parameters are quantified. CO is a fire tracer because it is significantly enhanced during fires. Data are available from 2007 to BAO tower data can be downloaded from NASA MODIS Fire Images MODIS fire images data visualize the transport direction of plumes from wildfires. A site with available fire images is earthdata.nasa.gov/data/ near-real-timedata/rapid-response. 2.2 Analysis Analysis tools: MATLAB, HYSPLIT, and GIOVANNI -MATLAB is a high-level language and interactive environment for numerical computations, visualization, and programming. MATLAB was used to analyze and visualize the ozone and fire data. Statistics of 8 hour average ozone and fire for the episodes were examined. All of the ozone data in different locations were processed, and the dates and sites when the 8-hour average ozone exceeds 75 ppbv were identified. Using the data from FINNv1, the numbers of fires and area burnt in Colorado and the Western U.S. were summarized. 7

8 -HYSPLIT (Hybrid Singe Particle Lagranian Integrated Trajectory Model) is a graphical user interface trajectory model developed by NOAA. A user inputs desired date and location into the model and the model displays the forward and backward trajectories of particles following wind vectors (web-link: ready.arl.noaa.gov/ HYSPLIT_traj.php; Draxler and Rolph, 2013; Roph, 2013). The HYSPLIT model was utilized to follow the movements of air mass originating from the locations of the fires. -GIOVANNI (web-link: disc.sci.gsfc.nasa.gov/giovanni; Acker and Leptoukh, 2007) is an interactive visualization and analysis that presents NASA MODIS aerosol optical depth for a given date or period. Aerosol optical depth is the degree to which aerosols prevent the transmission of light by absorption or scattering of light. Aerosols were a known product of fires (Andreae and Merlet, 2001), and tracing aerosol depth enabled the tracking of the range the wildfire influenced. 3. Results 3.1. High ozone events in summer of 2012 in Colorado According to the analysis of surface monitor ozone data in this study, there were 66 ozone violations (events of daily maximum of 8 hour average ozone > 75 ppbv) in the month of July in 2012 throughout Colorado s 34 surface monitoring sites near the Front Range region. Many of the violations are during days near July 4 th as demonstrated in Figure 1. 8

9 Ozone Concentration[ppb] a) at 34 sites Day of Month High Ozone Occurrence b) Figure 1. a) 8-hour averages of surface ozone at 34 monitoring sites in Colorado between July 1 st through July 6 th, 2012, with a visible violation line. b) High ozone events are spread across Front Range and Colorado Springs on July 4 th, > 75 ppbv, 75 >= > 65 ppbv, <= 65 ppbv 3.2. Wildland fires in summer of 2012 in Colorado and the Northwestern U.S. In the summer of 2012, there were many record-breaking wildfires in Colorado, as mentioned in the introduction (see also Figure 2a). After noting the high ozone and wildfires on July 4 th, a HYSPLIT model was conducted on the Waldo Canyon fire in Colorado in order to observe the movement of products of the wildfires. The wind trajectories from the HYSPLIT (Figure 2b) exhibited that the air mass traveled inside the state of Colorado. This most likely indicated that the ozone precursors 9

10 released from the Waldo Canyon fire were present in Colorado increasing the possibility of surface ozone formation. a) b) Figure 2. a) Area burnt (proportional to the size of red filled circle) in Colorado during a period of June 28 th -July 8 th, 2012 and b) The forward HYSPLIT trajectory model from the wildfires in Waldo Canyon, CO for the same period in a), showing the inner-state travel of air masses. 10

11 Although the Waldo Canyon Fire did release a series of ozone precursors in Colorado, the Colorado fire was not the only fire that might cause the multiple ozone violations. Figure 3 reveals other fires occurring in the Northwestern states. On July 4 th as an example, NASA s MODIS satellites captured wildfires and plume in Colorado, Wyoming, South Dakota, and Montana. Montana Wyoming S. Dakota Denver Colorado Springs MODIS : 7/4/2012 Figure 3. The image of occurring wildfires on July 4th captured by NASA s MODIS. To get a general visualization of the air plumes from the fire, GIOVANNI was used to observe the aerosol optical depth of July 4 th (Figure 4). The greater the aerosol optical depth means a greater number of aerosols, which are a product of forest fires. In Figure 4, there was a heavy concentration of aerosols in the North Western part of Colorado, which originated from the fires. This means that the ozone precursors released by the fires potentially traveled to Colorado. 11

12 Figure 4. MODIS aerosol optical depth from GIOVANNI run on July 4 th, GIOVANNI uses NASA satellite instruments Terra (right) and Aqua (left). When a HYSPLIT was done to track the air mass movement the day of the fires in Wyoming, South Dakota, and Montana, it was discovered that the wind trajectory from Wyoming fires starting from July 1 st were constantly carried into Colorado (Figure 5). During July 2 nd to July 4 th the wind traveling in Wyoming circled down to Northern Colorado. The emissions from South Dakota and Montana fires before July 4 th mostly traveled north to Canada. Thus, the ozone precursors from the Wyoming fire and the Waldo Canyon fire combined with the warm weather caused an intense concentration of ozone on July 4 th. 12

13 Figure 5. Forward HYSPLIT trajectory models, from July 2 nd to July 4 th (left to right). The models display air mass movement on the days of the Wyoming fire. Black circle denotes the location of the NOAA BAO tower. See Figure 6 for the BAO tower CO, CO 2, and O 3 data on the same period Chemical indications of fire impact on ozone on July 4 th, 2012 CO is an emission from fires that is commonly used as a footprint for tracking fires. Figure 6a shows the time series of CO, CO2, and O3 at BAO tower on July 4 th, More than 100 ppbv ozone was observed along with enhanced CO plumes (maximum of CO ~500 ppbv). Urban plumes tend to cause the enhancement of both CO and CO2. Figure 6a indicates that CO2 does not increase as much as CO. Thus, the high O3 on this date directly relates to the wildfires. The ratios of CO:CO2 in the air characterizes the type of emission source (Kim et al., 2011). If the slope of the line of best fit between CO (ppbv) and CO2 (ppmv) is approximately 10 (ppbv/ppmv), the origin of the air masses has been regarded as urban sources (e.g., automobiles). But when the slope is much greater than 10 (ppbv/ppmv), it can be considered that origins of air mass are fires. Figure 6b is a scatter plot of CO and CO2 for July The slope is the highest on July 4 th among the other days in July 2012, highlighting that the high ozone case was developed under the influence of wildfires. 13

14 CO [ppbv] CO [ppbv] CO [ppbv] O 3 [ppbv] CO2 [ppmv] CO [ppbv] a) m 100m 300m CO variation in CO2 variation in Day of Month 22m m 300m Ozone variation in Day of Month Day of Month b) m m high ozone event m high ozone event high ozone event CO2 [ppmv] CO2 [ppmv] CO2 [ppmv] Figure 6. a) Time series graphs from the BAO tower exhibiting the CO, CO 2, and O 3* on July 2-4. *Surface O 3 data were measured at the NOAA Platteville site nearby the tower. b) A scatter plot from BAO tower data. The plots are at different elevations and all have plotted CO, CO 2 ratios. The data on July 4 th between 8:25 and 19:40 MST are shown as the filled red circles. 14

15 3.4. Multi-year analysis of Colorado surface ozone and Western U.S. wildfires The July 2012 case (shown in ) exhibits the potential importance of both local and distant fires on the surface ozone in Colorado. In this section a more comprehensive analysis using the data for is summarized. Figures 7a and b indicate that the average ozone and the number of ozone violations in Colorado were highest in the summer of 2007 and The area burnt in the Western U.S exhibits the maximum in 2007 and similarly high values in 2008 and 2012 (Figure 8a). The area burnt in the summertime in Colorado is the greatest in 2012 due to the High Park fire in Fort Collins and the Waldo Canyon fire in Colorado Springs (Figure 8b). The year-to-year variations of the area burnt in the Western U.S are correlated to the trends in the O3 in Colorado. The monthly average CO at NOAA BAO tower (not shown in the manuscript) exhibits year-to-year variations similar to those of area burnt in the Western U.S, implying that emissions from distant fires across the Western U.S. are transported to Colorado. The minimum summertime air temperature is in 2009, which corresponds to the time of the minimum average O3 and number of violations. This suggests the potentially important role of meteorological factors on surface ozone in Colorado. However, the temperatures in 2011 and 2012 are similar in July and August, which does not agree with the increase of ozone from 2011 to The multi-year analysis suggests that the inter-annual variability of ozone in Colorado is correlated with the wildfires in the Western U.S. 15

16 O 3 [ppbv] Ozone violation count a) 70 b) June July August Year Year Figure 7. a) Monthly (June, July, and August) average ozone from 2007 to 2012 (34 monitoring sites) b) Number of ozone violations in each month from (34 monitoring sites) a) b) Figure 8. a) Area burnt in the Western U.S. from , categorized June, July, and August. b) Area burnt in Colorado from , categorized June, July, and August. [Note: area burnt maximum in a) is 33 times greater than the maximum in b)]. 4. Conclusions There were record-breaking wildfires in Colorado in 2012 such as High Park Wildfires in Fort Collins and Waldo Canyon fires in Colorado Springs. It has been known that aerosols from wildfires can cause visibility and health (cardiovascular and respiratory) issues. O3 precursors are also emitted in large amounts from fires. Understanding of influence of wildfires on surface ozone is needed because of the 16

17 growing air pollution resulting in the heavy surface ozone concentrations, causing more people with lung problems to be in hazardous conditions. The levels of surface ozone using EPA s measuring sites across Colorado were examined. In the summer of 2012, there were many exceptionally high ozone events in Colorado. There were 17 violations in June, 66 violations in July, and 32 violations in August for 34 EPA monitoring sites in which the data were consistently available for Analysis of fire count and area burnt data along with air trajectory model suggests that Waldo Canyon Fires near Colorado Springs along with wildfires nearby western states could cause many extreme events of high ozone in July The multi-year analysis of surface ozone and fire statistics data also highlight that not only Colorado fire have an impact on the surface ozone within Colorado, but other distant fires can influence the severe ozone violations in Colorado. NASA MODIS fire counts and aerosol optical depths from wildfires were enhanced in Colorado and nearby western states for high ozone (violation) period. The MODIS data were critical in understanding the time and location of fires and the spatial range of influence of wildfires through aerosol optical depth information. CO and CO2 data from NOAA BAO tower provides critical chemical evidence of wildfire impacts on ozone. In this study, the importance of wildfires outside of the state of Colorado (the Western U.S) were highlighted to have a substantial impact on Colorado s surface ozone as well the fires inside the state. There are several other factors that can affect surface ozone in Colorado during spring and summer. In May or June, ozone in the stratosphere was possibly intruded into the troposphere and over high plains such 17

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