Evidence for ≥C₃ alkyl nitrates in rural and remote atmospheres

Abstract

Interactions of odd-nitrogen compounds with non-methane hydro-carbons and a variety of radical species have been shown to have a potential impact on atmospheric chemistry on local, regional, and even global scales^1–9. To understand the interactions of atmospheric nitrogen compounds requires an accurate budget of individual reactive nitrogen species. But recent attempts to obtain a mass balance between total reactive nitrogen (NO_y) and individual reactive nitrogen species (NO-I-NO²+HNO³+PAN (peroxyacetyl nitrate) +PPN (peroxypropionyl nitrate) + particulate NO⁻₃) have not accounted for all NO^9,10_y. One class of compound proposed to account for some of the NO_y deficit is the alkyl nitrates (RONO²)^5,10–12, although ambient measurements have not been available to test this hypothesis. Here I report measurements of RONO2 made in the North Pacific atmosphere, providing the first direct evidence for existence and transport of ≥C³ alkyl nitrates in the troposphere. I also observed a variation in alkyl nitrate concentration which suggests these compounds may be used as unique tracers of 'polluted' air masses to remote areas. These observations are significant because relatively long-lived alkyl nitrates can serve as reservoirs of reactive nitrogen in the remote troposphere, where they can be converted to NO_x, a key catalyst in ozone formation and destruction^3,4.