Significant Latitudinal Gradient of Nitrate Production in the Marine Atmospheric Boundary Layer of the Northern Hemisphere

Atmospheric samples collected during 2017 and 2018 Chinese Arctic Expedition cruises are used to investigate the latitudinal gradients of nitrate (NO3-) sources and production in the marine atmospheric boundary layer of the Northern Hemisphere. Both concentration and isotopic composition (delta N-15, delta O-18, and Delta O-17) of atmospheric NO3- show significant latitudinal gradients. delta N-15 suggests that continental sources dominate atmospheric NO3- in both mid-and high-latitudes, while oceanic RONO2 emissions account for 21%-26% of the NO3- budget in mid-latitudes. Slightly higher delta N-15 in high-latitudes than in mid-latitudes indicates insignificant isotope effects of long-range atmospheric transport of NO3-. delta O-18 and Delta O-17 of NO3- are significantly higher in mid-latitudes than in high-latitudes, suggesting distinct main production pathways in the two regions. It is estimated that similar to 69% of NO3- is produced via NO2 + OH in the high-latitudes, while similar to 68% of NO3- is from N2O5 + H2O and NO3 + DMS/CH pathways in mid-latitudes.