With the help of self-developed highly sensitive instrumentation to measure trace gases, including reactive radicals that occur in minute amounts in ambient air, to uncover the photochemical reaction chains.

Also developing computer models to simulate the interactions of chemical and meteorological processes, and investigating the impact of atmospheric composition changes on climate and planetary health in the Anthropocene.

Jos Lelieveld coordinated major field measurement campaigns on atmospheric chemistry and climate ‘hot spot’ regions like the Indian Ocean, the Mediterranean, the Amazon and the Middle East.

[17][18][19] Lelieveld quantified the global impact of air pollution emission sectors on human health, identifying agriculture and residential energy use as important anthropogenic sources of particulate matter, next to the use of fossil fuels.

[20] Further, he showed the co-benefits of air pollution control on improving human health, reversing anthropogenically perturbed rainfall patterns and limiting global warming.

[21][22] His work on the Middle East and North Africa showed that the region is a global hotspot of climate change, weather extremes and air pollution, which could ultimately compromise human habitability[23][24] Lelieveld has an h-index of 108 (Google scholar, As of May 2022[update])[25]