This study presents a new method to estimate fossil fuel CO₂ (ffCO₂) emissions by modelling NO_x chemistry. Our regression models predict NO_x chemical rates and NO₂ : NO ratios with R² values above 0.95 using meteorological inputs. Incorporating these regressions reduces computational time compared to traditional methods and enables integration into model inversion frameworks. This scalable approach supports global emissions monitoring and climate change mitigation efforts.

Ozone depletion events (ODEs) and bromine explosions in the Arctic were studied for 2019/20. Our model underestimated boundary layer height and showed warm biases, affecting ODE simulation. Updates improved coastal ozone agreement but failed to capture strong ODEs. Bromine monoxide (BrO) was overestimated at the surface yet underestimated in columns. Long-term data show declining strong ODEs since 2008, suggesting additional climate-driven factors beyond sea ice age.

Identifying and quantifying methane emissions from urban sources is important for mitigating climate change. Using 6 years of winter and spring observations, we found that methane emissions from New York City are highly variable and underestimated compared to inventories, especially in winter, and correlate well with emissions of carbon monoxide (CO). Our results suggest a common urban incomplete combustion source for both methane and CO currently missing from emissions inventories.

Biomass burning is a significant source of greenhouse gases and airborne pollutants in Asia. Airborne measurements of greenhouse gas enhancement ratios, trace gases, and particle scattering were used to identify air masses impacted by biomass burning over several Asian countries during February and March of 2024. Further analysis using atmospheric transport models and satellite hotspot products was performed to understand the transport history of biomass burning impacted airmasses over Thailand.

Highly oxygenated organic molecules by atmospheric oxidation of plant emitted monoterpenes are important components in secondary organic aerosol formation. Autoxidation of organic peroxy radicals is one important pathway of their formation. We show that isomerization of highly oxygenated alkoxy radicals leads to highly oxygenated peroxy radicals that continue the autoxidation chain. Alkoxy-peroxy steps may dominate the formation of highly oxygenated molecules at high nitrogen oxide levels.

We investigate the distribution of CO₂ in the upper troposphere and lower stratosphere using both, observations and an atmospheric model. Simulating an artificial tracer, we separate CO₂ seasonality from long-term trend and transport variability. We found that patterns in the seasonal signal are attributable to large-scale transport features like the subtropical jet or the Brewer-Dobson circulation. Being a powerful diagnostic tool we recommend to use this tracer for model intercomparisons.