Abstract
Abstract. Space-borne measurements of tropospheric nitrogen dioxide (NO2) columns are up to 10x more sensitive to upper tropospheric (UT) NO2 than near-surface NO2 over low-reflectivity surfaces. Here, we quantify the effect of adding simulated lightning NO2 to the a priori profiles for NO2 observations from the Ozone Monitoring Instrument (OMI) using modeled NO2 profiles from the Weather Research and Forecasting–Chemistry (WRF-Chem) model. With observed NO2 profiles from the Deep Convective Clouds and Chemistry (DC3) aircraft campaign as observational truth, we quantify the bias in the NO2 column that occurs when lightning NO2 is not accounted for in the a priori profiles. Focusing on late spring and early summer in the central and eastern United States, we find that a simulation without lightning NO2 underestimates the air mass factor (AMF) by 25 % on average for common summer OMI viewing geometry and 35 % for viewing geometries that will be encountered by geostationary satellites. Using a simulation with 500 to 665 mol NO flash−1 produces good agreement with observed NO2 profiles and reduces the bias in the AMF to < ±4 % for OMI viewing geometries. The bias is regionally dependent, with the strongest effects in the southeast United States (up to 80 %) and negligible effects in the central US. We also find that constraining WRF meteorology to a reanalysis dataset reduces lightning flash counts by a factor of 2 compared to an unconstrained run, most likely due to changes in the simulated water vapor profile.
Highlights
NOx (≡ NO + NO2) is a short-lived trace gas in the atmosphere
Profiles used are those derived by binning WRF-Chem output from the entire domain for simulations with 0, 500, and 665 mol NO flash−1 without four-dimensional data analysis (FDDA) nudging (Fig. 1)
The changes we find in the tropospheric vertical column density (VCD) due to the inclusion or exclusion of lightning NO2 from the a priori profiles exceed the uncertainty in ∼ 50 % of the domain; the changes in the air mass factor (AMF) exceed the uncertainty in ∼ 70 % of the domain
Summary
NOx (≡ NO + NO2) is a short-lived (typical summer lifetime 2–7 h) trace gas in the atmosphere. Space-borne measurements of NO2 as an indicator of total NOx, such as those from the Global Ozone Monitoring Experiment (GOME and GOME-2), SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY), and Ozone Monitoring Instrument (OMI), are a valuable tool in understanding NOx emissions and chemistry because of their global reach and long data records Use of these observations includes assessment of NOx chemistry (e.g., Beirle et al, 2011; Valin et al, 2013) anthropogenic emissions (e.g., Miyazaki et al, 2012; Russell et al, 2012; Lu et al, 2015; Liu et al, 2016, 2017) and natural emissions (e.g., Martin et al, 2007; Beirle et al, 2011; Hudman et al, 2012; Mebust et al, 2011; Mebust and Cohen, 2013, 2014; Miyazaki et al, 2014; Zörner et al, 2016). This final step accounts for the effect of variable path length
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