Can a Weekly Cycle in Pollutants be Observed Offshore the U.S. East Coast with Airborne Measurements?

Varying anthropogenic emissions during a typical week can lead to shifts in aerosol properties, yet such signals are rarely examined in marine outflow regions. Since aerosol data from the IMPROVE network along the U.S. East Coast show weekday peaks in anthropogenically influenced aerosol species, this study leverages airborne measurements from NASA’s ACTIVATE campaign (2020–2022) to investigate weekly cycles of aerosol properties over the Northwest Atlantic Ocean. Analysis focuses on winter and summer flights that sampled continental outflow along repeated transects between NASA Langley Research Center (LaRC) and two aviation waypoints (ZIBUT and OXANA). Aerosol number concentration (N) between 0.1 and 1 μm (N0.1–1 μm), NCCN at 0.37–0.43% supersaturation, and aerosol surface area concentration (SA0.003–1 μm) show midweek peaks for LaRC-OXANA and LaRC-ZIBUT, with minima on Sunday/Monday. However, the most pronounced weekly cycle for both corridors was for variables relevant to new particle formation (NPF: N3 nm, N3 nm–N10 nm, N0.01–0.1 μm, N3:N10, where N3:N10 is the ratio of particles greater than 3 nm to those greater than 10 nm), which peak earlier in the week (Sunday/Monday) and decrease into the work week. While IMPROVE data show a weekly cycle for many variables along the coast (PMcoarse, PM2.5, fine soil, sulfate, and nitrate), airborne data show that organics exhibit consistent peaks on Thursday and minima on Sunday for both corridors. The weekly cycles are generally robust (especially NPF-related variables) when isolating wintertime data and when dividing LaRC-OXANA and LaRC-ZIBUT corridors in half. The results provide evidence for a weekly cycle for some aerosol characteristics offshore of a major continent with implications for cloud microphysics, remote sensing, and downwind air quality.