No abstract

As Arctic temperatures rise at twice the global rate, sea ice is diminishing more quickly than models can predict. Processes that dictate Arctic cloud formation and impacts on the atmospheric energy budget are poorly understood, yet crucial for evaluating the rapidly changing Arctic. In parallel, warmer temperatures afford conditions favorable for productivity of microorganisms that can effectively serve as ice nucleating particles (INPs). Yet the sources of marine biologically derived INPs remain largely unknown due to limited observations. Here we show, for the first time, how biologically derived INPs were likely transported hundreds of kilometers from deep Bering Strait waters and upwelled to the Arctic Ocean surface to become airborne, a process dependent upon a summertime phytoplankton bloom, bacterial respiration, ocean dynamics, and wind‐driven mixing. Given projected enhancement in marine productivity, combined oceanic and atmospheric transport mechanisms may play a crucial role in provision of INPs from blooms to the Arctic atmosphere.

Abstract. Vehicle emissions have been identified as an important urban source of ammonia (NH3). However, there are large uncertainties regarding the contribution of vehicle emissions to urban NH3 budgets, as well as the role of NH3 in spatiotemporal fine particulate matter (PM2.5) formation and nitrogen (N) deposition patterns. The N stable isotopic composition (δ15N) may be a useful observational constraint to track NH3 emission sources and chemical processing, but previously reported vehicle δ15N(NH3) emission signatures have reported a wide range of values, indicating the need for further refinement. Here we have characterized δ15N(NH3) spatiotemporal variabilities from vehicle plumes in stationary and on-road measurements in the USA and China using an active NH3 collection technique demonstrated to accurately characterize δ15N(NH3) on the order of hourly time resolution. Significant spatial and temporal δ15N(NH3) variabilities were observed and suggested to be driven by vehicle fleet composition and influences from NH3 dry deposition on tunnel surfaces. Overall, a consistent δ15N(NH3) signature of 6.6±2.1 ‰ (x‾±1σ; n=80) was found in fresh vehicle plumes with fleet compositions typical of urban regions. Our recommended vehicle δ15N(NH3) signature is significantly different from previous reports. This difference is due to a large and consistent δ15N(NH3) bias of approximately −15.5 ‰ between commonly employed passive NH3 collection techniques and the laboratory-tested active NH3 collection technique. This work constrains the δ15N(NH3) urban traffic plume signature, which has important implications for tracking vehicle NH3 in urban-affected areas and highlights the importance of utilizing verified collection methods for accurately characterizing δ15N(NH3) values.