Hamilton, Tamryn, Jaars, Kerneels, van Zyl, Pieter G., Aurela, Mika, Adon, Marcellin, Beukes, Johan P., Josipovic, Miroslav, Feig, Gregor T., Kulmala, Markku, Laakso, Lauri, Vakkari, Ville
Abstract. South Africa is a global hotspot for anthropogenic atmospheric NO2, where emissions from the industrialised Mpumalanga Highveld influence air quality across the southern African region. In the atmosphere, NO2 is a key player in oxidative chemistry and contributes to particulate nitrate formation and the biogeochemical nitrogen cycle through deposition. At the same time, various ecosystem processes act as sources and sinks of NO and NO2. The net result of these factors implies differences in the ecosystem scale flux of NO2. Here we perform the first-ever high-resolution NO2 measurements with a quantum cascade laser (QCL) instrument in a grazed African savannah landscape from 2015 to 2020. Micrometeorological eddy covariance measurements were used to quantify the NO2 flux and explore temporal trends at diurnal, monthly, seasonal and interannual scales. Our findings highlight the variability of NO2 flux within this system, with notable interannual change observed at both monthly and hourly scales. Seasonal differences in NO2 flux and deposition velocity were strongly linked to the rainfall season, with negligible differences between dry season months. Diurnal flux trends peaked during daylight hours, with consistently low NO2 flux during nighttime. These findings contribute to our understanding of near-surface atmospheric NO2 dynamics in arid landscapes and, for the first time, can be used to estimate ecosystem-scale compensation point of NO2.