CMAQ Modeling and Analysis of Trace Gases and Biomass Burning



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The Community Multiscale Air Quality (CMAQ) model was extended to simulate nitrous acid (HONO) and nocturnal isoprene in Houston, and biomass burning over the United States (U.S.). The linear dependence of HONO heterogeneous reaction on the relative humidity (RH) was parameterized by scaling the reaction rate. The simulation scenarios conducted for September 2013 in Houston improved modelled-HONO concentrations and reduce the bias for NO2 compared to observations. Similarly, simulations were conducted for nocturnal isoprene in September 2013 using the U.S. Environmental Protection Agency’s (EPA’s) National Emissions Inventory of 2011 (NEI 2011). The results were evaluated against measurements collected at eight Automated Gas Chromatographs sites maintained by the Texas Commission on Environmental Quality. The comparisons demonstrated an overestimation before midnight versus an underestimation after midnight. Analyses identified the underestimated wind speed as the major factor contributing to the overestimation of simulated isoprene, and uncertainties in the nocturnal isoprene anthropogenic emissions in the NEI 2011 over industrial areas in Houston as the major factor contributing to the underestimation. A sensitivity experiment with adjusted anthropogenic emissions of isoprene in the later part of the night yielded closer isoprene predictions after midnight. Finally, an offline physical plumerise module was applied to the Fire Inventory from NCAR (FINN) to simulate an intense fire episode in August 2012 in the western U.S. It was found that the base simulation with default FINN emissions underestimated the CO concentrations in the mid-troposphere. The sensitivity experiment increasing fire emissions by a factor of five improved the model simulation, whereas the experiment reducing plume height showed little change. Model results indicated that during the fire event more than 40 ppb O3 were generated near the fire sources. Three-year simulations from April to October 2012–2014 showed the contributions of biomass burning to the mean maximum daily 8-hour (MDA8) surface O3 and the ambient fine particulate matter (PM2.5) was limited to regional scales. Near the fire sources, the contributions to PM2.5 and MDA8 were more than 20 µg m-3 and 8–9 ppb, respectively for wildfires, and 10–12 µg m-3 and 3–4 ppb, respectively for prescribed fires.



HONO, Isoprene, Biomass burning


Portions of this document appear in: Diao, Lijun, Yunsoo Choi, Beata Czader, Xiangshang Li, Shuai Pan, Anirban Roy, Amir Hossein Souri, Mark Estes, and Wonbae Jeon. "Discrepancies between modeled and observed nocturnal isoprene in an urban environment and the possible causes: A case study in Houston." Atmospheric Research 181 (2016): 257-264. And in: Diao, Lijun, Anirban Roy, Beata Czader, Shuai Pan, Wonbae Jeon, Amir Hossein Souri, and Yunsoo Choi. "Modeling the effect of relative humidity on nitrous acid formation in the Houston area." Atmospheric environment 131 (2016): 78-82.