Photodissociation and quantum yield determination of peroxyacetyl nitrate

Abstract

Peroxyacetyl nitrate (PAN) is an important atmospheric species due to its role in global transport of reactive nitrogen oxides, NOx (= ·NO₂ + ·NO). Peroxyacetyl nitrate is formed by reactions involving hydrocarbons and ·NO₂ in polluted regions and can be transported into the Arctic. To understand the role of PAN as a transporter of NOx to the Arctic, we need to quantify its decomposition pathways which include: thermal decomposition, photolysis, and reaction with the hydroxyl radical (·OH). In colder regions, such as the Arctic, the most rapid decomposition pathway is photolysis. Several photolytic pathways are possible for PAN. We photolyzed PAN in the laboratory using a frequency-doubled tunable dye laser. A highly sensitive technique called cavity ring-down spectroscopy (CRDS) probed the ·NO₃ produced in the photolysis reaction and we quantified the quantum yield for production of ·NO₃. The quantum yield is the fraction of photoexcited molecules that decompose to a certain chemical product. We determined that the quantum yield of ·NO₃ at 289 nm is 0.30 [plus/minus] 0.08. These results are discussed in context of previous work on PAN photolysis and in terms of a mechanistic model.