Hourly observations of HONO and NO2 in fire plumes as detected by GEMS and TEMPO

Nitrous acid (HONO) is a key atmospheric species primarily due to its role as a source of OH through its rapid photolysis. OH is the atmosphere’s primary oxidant: it plays a central role in breaking down pollutants and greenhouse gases, and at the same time, it is a key ingredient to photochemical smog and ozone formation. Despite recent scientific progress, the emission budget and formation mechanisms of HONO are poorly constrained and consequently the impact of HONO emissions on tropospheric chemistry remains uncertain although it is believed to be important.

With the advent of high-spatial resolution hyperspectral space sensors, it becomes possible to detect short-lived species as HONO from large emission sources such as fires. This has been demonstrated on the global scale using the Sentinel-5 Precursor/TROPOMI instrument. Hourly observations from geostationary instruments, like GEMS and TEMPO, with a similar or even better spatial resolution than TROPOMI, opens new possibilities in terms of research and algorithmic developments. Understanding the time evolution of HONO emissions and conversion into NO_x and how this relates to the fire activity and plume composition is particularly interesting.

Here, we present our progress in improving and interpreting HONO space-based data. We focus not only on HONO but also on the retrieval of NO₂ in the same spectral range as HONO, using an innovative algorithm (CO-DOAS). The objective is to estimate the enhancement ratio of HONO to NO₂ andstudy its relation to the fire intensity both in space and time. We also assess the consistency of GEMS and TEMPO HONO (and HONO/NO₂) results with TROPOMI observations.Finally, we briefly discuss the possibility of new HONO observations from future satellite platforms.