Development of a new approach to quantify organic nitrate yields from RO2+NO reactions – Application to ethane-, cyclohexane- and isoprene-derived RO2 radicals

Organic peroxy radicals (RO₂) are key species in the troposphere as their chemistry leads to the formation of secondary organic aerosols and ozone. RO₂ radicals mainly react with nitric oxide (NO) in the lower troposphere, leading to either (i) radical propagation, which sustains the atmospheric oxidation capacity, or (ii) the formation of organic nitrates (RONO₂), where both RO₂ and NO₂ are sequestered, thus reducing radical propagation rates and the formation of secondary pollutants. The latter pathway exhibits RONO₂ yields ranging from negligible up to 35%, depending on the RO₂ molecular structure.

We propose a new approach to quantify RONO₂ yields from RO₂+NO reactions, taking advantage of the measurement principle of chemical amplifiers (CA), initially developed for measuring ambient concentrations of RO_x radicals (OH, HO₂ and RO₂). We will show that the CA can be used as a  kinetic apparatus to quantify an “integrated” RONO₂ yield for chemical systems where a specific volatile organic compound (VOC) is oxidized by OH. In this presentation, we will discuss applications for the following chemical systems: ethane+OH, cyclohexane+OH and isoprene+OH, emphazing how the determinations contrast to published data. Both advantages and drawbacks will be highlighted for this new approach.