Wendell’s research broadly focuses on understanding the impacts humans have had on the composition of the atmosphere, biosphere, and climate. He is particularly interested in quantifying atmospheric trace gas emission sources of reactive nitrogen including nitrogen oxides (NOx) and ammonia (NH3) and understanding their atmospheric removal processes. This is important due to the impacts trace gas emissions have on urban air quality, on influencing the concentrations of atmospheric oxidants, and on the environment (e.g. acid rain, drinking water degradation, soil acidification, eutrophication, and biodiversity changes in the terrestrial ecosystem). His research is interested in answering questions such as (1) how have humans altered the biogeochemical cycling of key biogeochemistry elements such as nitrogen? (2) how have humans altered the atmospheric reactions responsible for the removal of atmospheric trace gases? (3) can we quantify trace gas emission sources to help guide future emission regulations? and (4) what are the connections between air quality and the climate system? To address these questions, Wendell utilizes stable isotopes to “fingerprint” various trace gas emission sources and atmospheric removal processes such as chemical reactions and photolysis. Applying these “fingerprints" to atmospheric chemistry models and ice core measurements enables the evaluation of global biogeochemical cycling and the assessment of atmospheric oxidation pathways and processes on the order of a few days to tens of thousands of years.