Short-lived organic nitrates in a suburban temperate forest: an indication of efficient assimilation of reactive nitrogen by the biosphere?

Abstract

Alkyl nitrates (ANs) and peroxycarboxylic nitric anhydrides (PANs) are important reservoirs of reactive nitrogen that contribute significantly to the rate of formation and growth of secondary organic aerosols and support the transport of reactive nitrogen from polluted areas to remote areas. It is therefore critical to understand their sources and sinks in different environments. In this study we use measurements of OH, O3, NO3 reactivity, volatile organic compounds, PANs and PPANs during the ACROSS (Atmospheric ChemistRy Of the Suburban foreSt) campaign to investigate different production and loss processes of ANs and PANs in a temperate forest. During the daytime OH-initiated processes were the dominant source of ANs (69 %–72 %), followed by NO3 (18 %–20 %) and O3 (8 %–12 %). During the nighttime the contribution from OH decreased to 43 %–53 %, and NO3 increased to 26 %–40 % with that of O3 largely unchanged. Of the measured PPANs, 48 %–78 % were modelled to be peroxyacetic nitric anhydride (PAN, commonly known as peroxyacetyl nitrate). Physical loss (e.g. deposition) was an important sink for both ANs and PANs and contributed significantly to the very short lifetimes of 1–4 h for ANs and 0.08–1.5 h for PANs observed during the campaign.