Katye E. Altieri

Impacts of Atmospheric Anthropogenic Nitrogen on the Open Ocean

Increasing quantities of atmospheric anthropogenic fixed nitrogen entering the open ocean could account for up to about a third of the oceans external (nonrecycled) nitrogen supply and up to ∼3% of the annual new marine biological production, ∼0.3 petagram of carbon per year. This input could account for the production of up to ∼1.6 teragrams of nitrous oxide (N2O) per year. Although ∼10% of the oceans drawdown of atmospheric anthropogenic carbon dioxide may result from this atmospheric nitrogen fertilization, leading to a decrease in radiative forcing, up to about two-thirds of this amount may be offset by the increase in N2O emissions. The effects of increasing atmospheric nitrogen deposition are expected to continue to grow in the future.

Link between isoprene and secondary organic aerosol (SOA): Pyruvic acid oxidation yields low volatility organic acids in clouds

[1]xa0Aqueous-phase oxidation (in clouds and aerosols) is a potentially important source of organic aerosol and could explain the atmospheric presence of oxalic acid. Methylglyoxal, a water-soluble product of isoprene, oxidizes further in the aqueous phase to pyruvic acid. Discrepancies in the literature regarding the aqueous-phase oxidation of pyruvic acid create large uncertainties in the in-cloud yields of secondary organic aerosol (SOA) and oxalic acid. Resolving the fate of aqueous-phase pyruvic acid is critical to understanding SOA formation through cloud processing of water-soluble products of isoprene, other alkenes and aromatics. In this work, aqueous-phase photochemical reactions of pyruvic acid and hydrogen peroxide at pH values typical of clouds were conducted and demonstrated that photochemical oxidation of pyruvic acid yields glyoxylic, oxalic, acetic and formic acids. Oxalic and glyoxylic acids remain mostly in the particle phase upon droplet evaporation. Thus isoprene is an important precursor of in-cloud SOA formation.

Secondary organic aerosol yields from cloud‐processing of isoprene oxidation products

[1]xa0While there is a growing understanding from laboratory studies of aqueous phase chemical processes that lead to secondary organic aerosol (SOA) formation in cloud droplets (SOAdrop), the contribution of aqueous phase chemistry to atmospheric SOA burden is yet unknown. Using a parcel model including a multiphase chemical mechanism, we show that SOAdrop carbon yields (Yc) from isoprene (1) depend strongly on the initial volatile organic carbon (VOC)/NOx ratio resulting in 42% > Yc > 0.4% over the atmospherically-relevant range of 0.25 < VOC/NOx < 100; (2) increase with increasing cloud-contact time; (3) are less affected by cloud liquid water content, pH, and droplet number. (4) The uncertainty associated with gas/particle-partitioning of semivolatile organics introduces a relative error of −50% ≤ ΔYc < +100 %. The reported yields can be applied to air quality and climate models as is done with SOA formed on/in concentrated aerosol particles (SOAaer).