Megan Schiede

Throughout 2020, ambient air pollution was reduced as a result from limiting anthropogenic activities to mitigate the spread of COVID-19. Not all air pollution is created the same as measurements of particulate matter 2.5 (PM2.5) were generally unaffected by this reduction due to PM2.5's source from wildfires. Despite influences from COVID-19 lockdowns, rises in PM2.5 concentrations can be attributed to the anomalously active wildfire season of 2020. As climate change progresses, these extraordinarily active seasons can be classified as the "new normal"; thus, comprehension of such events are vital.

Given the ability of lightning to naturally cause wildfires, there exists a positive feedback loop that exists as convection can be influenced by aerosols. To understand this feedback loop, a proper analysis of the interactions between lightning and wildfires is necessary. Data from the Environmental Protection Agency (EPA) Air Quality System, National Lightning Detection Network (NLDN), and the ERA5 Reanalysis was utilized for a statistical analysis. Airports were carefully chosen to result in 132 correlation coefficients for either PM2.5 concentration or lightning strikes to meteorological variables and month. Planetary boundary layer height (PBLH) had the strongest negative correlation with all but one calculated correlation being negative on the East Coast.

Numerical modeling methods were implemented to understand aerosol behavior beyond a statistical scope. Two Weather Research and Forecasting (WRF) model simulations were conducted surrounding the Detroit Metropolitan Wayne County Airport (KDTW) using a 3-km High Resolution Rapid Refresh (HRRR) initialization at 0000 UTC 7 September 2020 to compare model runs with and without the inclusion of NASA's Goddard Earth Observing System (GEOS) model aerosol data. The difference between the simulations including aerosols to no aerosols showed that PBLH mimicked the frontal structure associated with convection for the case. Positive values indicated that WRF simulations that included aerosols had higher PBLH that were observed behind the cold front. Additional cases must be examined to draw adequate conclusions regarding numerical model output to further confirm the existence of a frontal-based relationship surrounding PBLH.

Methyl chloroform (CH3CCl3) was a commonly used solvent and degreasing agent prior to its classification as an ozone depleting substance, and subsequent prohibition by the Montreal Protocol in 1987. With an atmospheric lifetime of five to six years, temporal measurements of methyl chloroform illustrate the success of these restrictions as background values fell from approximately 130 ppt in the early 1990s to 1.5 ppt in 2020. The COVID-19 lockdowns brought about an ease in EPA restrictions, as well as a new opportunity for the NASA Student Airborne Research Program to extend whole air sampling across the United States. The results from this widespread sampling discovered enhanced concentrations of methyl chloroform near various highly populated coastal areas with the highest observed in Ithaca, NY at 16.4 ppt. Given the status of methyl chloroform as an ozone depleting substance, its use requires permission from the EPA implying its use should be easy to track. An investigation into past uses of methyl chloroform was conducted to determine if any plausible sources for these enhanced concentrations still currently exist. To confirm the validity of these sources, multiple NOAA HYSPLIT trajectories were run on the dates of enhanced observations. There are promising associations between the location of potential emission sources and enhanced methyl chloroform measurements. In order to further support these results additional whole air sampling must be conducted near sites of interest.