Ice nucleating particles strongly influence cirrus cloud properties but remain difficult to measure at cirrus temperatures. By combining EMAC (ECHAM/MESSy Atmospheric Chemistry) model simulations with in situ observations from the CIRRUS-HL (Cirrus in High-Latitudes) campaign, we investigate aerosol-cirrus interactions across latitudes. While the model generally agrees with observations, it overestimates ice crystal number concentrations detrained from convection, which we correct applying a new radius-temperature parametrization from the observations.

This study improves GEOS-Chem simulations of PM_2.5–temperature sensitivity and identifies key processes driving regional variability across the US. We show that chemical production dominates in the east, primary emissions in the west, and transport processes affect interannual variability. Results highlight the need for accurate temperature-dependent process representation in air quality models.

Since 2013, China’s Clean Air Action has altered land carbon uptake. Our modeling shows that while aerosols and nitrogen deposition previously boosted the carbon sink, their effects have weakened. Conversely, ozone's negative impact has grown. This shifts the overall atmospheric influence from enhancement to suppression. Controlling ozone is thus key for dual benefits in clean air and carbon neutrality.