| Popis: |
Lightning is one of the primary natural sources of nitrogen monoxide (NO), and the influence of lightning-induced NO (LNO) emission on air quality has been investigated in the past few decades. In the current study an LNO emissions model, which derives LNO emission estimates from satellite-observed lightning optical energy, is introduced. The estimated LNO emission is employed in an air quality modeling system to investigate the potential influence of LNO on tropospheric ozone. Results show that lightning produces 0.174 Tg N of nitrogen oxides (NOx = NO + NO2) over the contiguous U.S. (CONUS) domain between June and September 2019, which accounts for 11.4 % of the total NOx emission. On average, LNOx emission increases tropospheric ozone concentration by 1–2 % (or 0.3–1.5 ppb) in the column; the enhancement is maximium at ~4 km above ground level, with a minimum near the surface. The southeast U.S. has the most significant ground-level ozone increase, with up to 1 ppb (or 2 % of the mean observed value) difference for the maximum daily 8-hour average (MDA8) ozone. However, many of these numbers are near the lower bound of the uncertainty range given in previous studies, suggesting the current LNO production rate used in the LNO emissions model may need to be adjusted. Moreover, the episodic impact of LNO on tropospheric ozone can be considerable. Performing backward trajectory analyses revealed two main reasons for the significant ozone increase: long-distance chemical transport and lightning activity in the upwind direction shortly before the event. In addition, the mixing of high LNOx (or ozone) plumes is likely another reason for ozone enhancement. |
