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 (δ¹⁵N, δ¹⁸O, and Δ¹⁷O) of atmospheric NO₃⁻ show significant latitudinal gradients. δ¹⁵N 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 δ¹⁵N in high-latitudes than in mid-latitudes indicates insignificant isotope effects of long-range atmospheric transport of NO₃⁻. δ¹⁸O and Δ¹⁷O 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 ∼69% of NO₃⁻ is produced via NO₂ + OH in the high-latitudes, while ∼68% of NO₃⁻ is from N₂O₅ + H₂O and NO₃ + DMS/CH pathways in mid-latitudes.