Quantification of lightning-produced NO_<i>x</i> over the Pyrenees and the Ebro Valley by using different TROPOMI-NO₂ and cloud research products

<p>Lightning, one of the major sources of nitrogen oxides (NO<span class="inline-formula">_<i>x</i></span>) in the atmosphere, contributes to the tropospheric concentration of ozone and to the oxidizing capacity of the atmosphere. Lightning produces between 2 and 8 Tg N yr<span class="inline-formula">⁻¹</span> globally and on average about 250 <span class="inline-formula">±</span> 150 mol NO<span class="inline-formula">_<i>x</i></span> per flash. In this work, we estimate the moles of NO<span class="inline-formula">_<i>x</i></span> produced per flash (LNO<span class="inline-formula">_<i>x</i></span> production efficiency) in the Pyrenees (Spain, France and Andorra) and in the Ebro Valley (Spain) by using nitrogen dioxide (NO<span class="inline-formula">₂</span>) and cloud properties from the TROPOspheric Monitoring Instrument (TROPOMI) as well as lightning data from the Earth Networks Global Lightning Network (ENGLN) and from the EUropean Co-operation for LIghtning Detection (EUCLID). The Pyrenees are one of the areas in Europe with the highest lightning frequencies, which, along with their remoteness as well as their very low NO<span class="inline-formula">_<i>x</i></span> background, enables us to better distinguish the LNO<span class="inline-formula">_<i>x</i></span> signal produced by recent lightning in TROPOMI NO<span class="inline-formula">₂</span> measurements. We compare the LNO<span class="inline-formula">_<i>x</i></span> production efficiency estimates for eight convective systems in 2018 using two different sets of TROPOMI research products provided by the Royal Netherlands Meteorological Institute (KNMI) and the Deutsches Zentrum für Luft- und Raumfahrt (DLR). According to our results, the mean LNO<span class="inline-formula">_<i>x</i></span> production efficiency in the Pyrenees and in the Ebro Valley, using a 3 h chemical lifetime, ranges between 14 and 103 mol NO<span class="inline-formula">_<i>x</i></span> per flash from the eight systems. The mean LNO<span class="inline-formula">_<i>x</i></span> production efficiency estimates obtained using both TROPOMI products and ENGLN lightning data differ by <span class="inline-formula">∼</span> 23 %, while they differ by <span class="inline-formula">∼</span> 35 % when using EUCLID lightning data. The main sources of uncertainty when using ENGLN lightning data are the estimation of background NO<span class="inline-formula">_<i>x</i></span> that is not produced by lightning and the time window before the TROPOMI overpass that is used to count the total number of lightning flashes contributing to freshly produced LNO<span class="inline-formula">_<i>x</i></span>. The main source of uncertainty when using EUCLID lightning data is the uncertainty in the detection efficiency of EUCLID.</p>