Evaluating NO_x emissions and their effect on O₃ production in Texas using TROPOMI NO₂ and HCHO

Abstract

Abstract. The Tropospheric Monitoring Instrument (TROPOMI) on the Sentinel-5 Precursor (S5P) satellite is a valuable source of information to monitor the NOx emissions that adversely affect air quality. We conduct a series of experiments using a 4×4 km2 Comprehensive Air Quality Model with Extensions (CAMx) simulation during April–September 2019 in eastern Texas to evaluate the multiple challenges that arise from reconciling the NOx emissions in model simulations with TROPOMI. We find an increase in NO2 (+17 % in urban areas) when transitioning from the TROPOMI NO2 version 1.3 algorithm to the version 2.3.1 algorithm in eastern Texas, with the greatest difference (+25 %) in the city centers and smaller differences (+5 %) in less polluted areas. We find that lightning NOx emissions in the model simulation contribute up to 24 % of the column NO2 in the areas over the Gulf of Mexico and 8% in Texas urban areas. NOx emissions inventories, when using locally resolved inputs, agree with NOx emissions derived from TROPOMI NO2 version 2.3.1 to within 20 % in most circumstances, with a small NOx underestimate in Dallas–Fort Worth (−13 %) and Houston (−20 %). In the vicinity of large power plant plumes (e.g., Martin Lake and Limestone) we find larger disagreements, i.e., the satellite NO2 is consistently smaller by 40 %–60 % than the modeled NO2, which incorporates measured stack emissions. We find that TROPOMI is having difficulty distinguishing NO2 attributed to power plants from the background NO2 concentrations in Texas – an area with atmospheric conditions that cause short NO2 lifetimes. Second, the NOx/NO2 ratio in the model may be underestimated due to the 4 km grid cell size. To understand ozone formation regimes in the area, we combine NO2 column information with formaldehyde (HCHO) column information. We find modest low biases in the model relative to TROPOMI HCHO, with −9 % underestimate in eastern Texas and −21 % in areas of central Texas with lower biogenic volatile organic compound (VOC) emissions. Ozone formation regimes at the time of the early afternoon overpass are NOx limited almost everywhere in the domain, except along the Houston Ship Channel, near the Dallas/Fort Worth International airport, and in the presence of undiluted power plant plumes. There are likely NOx-saturated ozone formation conditions in the early morning hours that TROPOMI cannot observe and would be well-suited for analysis with NO2 and HCHO from the upcoming TEMPO (Tropospheric Emissions: Monitoring Pollution) mission. This study highlights that TROPOMI measurements offer a valuable means to validate emissions inventories and ozone formation regimes, with important limitations.

Derivation of Emissions From Satellite‐Observed Column Amounts and Its Application to TROPOMI NO2 and CO Observations

“…The NO x emissions are derived using TROPOMI NO 2 TVCD from May 2018 to July 2022 over the CONUS as shown in Figure 2. A constant NO x :NO 2 ratio of 1.32 is used to convert the TROPOMI NO 2 TVCD to the corresponding NO x column amount as done in many observation‐based studies (Beirle et al., 2011, 2019; Dix et al., 2022; Goldberg, Lu, et al., 2019; Goldberg et al., 2022). A more realistic ratio can be readily applied as a post‐processing step because the estimated emission is a linear function of column amount (Equation ).…”

“…Horizontal winds at 100 and 10 m above the surface from the ERA5 reanalysis at 0.25° resolution (Hersbach et al, 2020) are spatiotemporally interpolated at TROPOMI level 2 observations. The 100-m wind is widely used to characterize the horizontal transport in the planetary boundary layer (PBL) (Dix et al, 2022;Goldberg et al, 2020Goldberg et al, , 2022Sun et al, 2021). The 10-m wind is used as the near-surface wind.…”

Elucidating the impacts of COVID-19 lockdown on air quality and ozone chemical characteristics in India

“…84 This can be due in part to the model underestimation of formaldehyde 86 and the calculation of the air mass factor in the satellite data. 87 Furthermore, a longer period (than one month) needs to be studied for evaluating the results as future work. It should also be mentioned that while these measurable FNR estimates can be used for identifying the chemical regimes, their limitations should be kept in mind.…”

Impact of Hurricane Ida on Nitrogen Oxide Emissions in Southwestern Louisiana Detected from Space

“…This study presents a quantitative analysis of top-down derived NO x emission changes in two urban areas in Louisiana, New Orleans and Baton Rouge, affected by Hurricane Ida. An exponentially modified Gaussian (EMG) function is utilized to estimate the NO x emission changes to illustrate its use for quick quantification of the complex emission dynamics caused by short-lived extreme weather events. − The results shown here are from the first analysis quantifying hurricane-driven emission changes of anthropogenically produced NO x using the EMG function.…”