Organic nitrates: Atmospheric importance and laboratory studies
Ozone in the troposphere is an essential constituent that helps determine the atmosphere's oxidizing power, but it is also a contaminant responsible for part of global warming, crop damage and causes respiratory problems. The ozone concentration has steadily increased over the last century, reaching levels where plant damage occurs.
It is known that VOCs (volatile organic compounds) and NOx (NO and NO2) from industrial as well as biogenic sources make control of regional tropospheric ozone difficult. For this reason, it is important to understand the mechanism for VOC oxidation, and the relationship between molecular structure and atmospheric radical chemistry. Tropospheric ozone is formed from the OH oxidation of VOCs in the presence of NO. Organic nitrates are also formed through this process. Formation of organic nitrates is a termination step, which competes with ozone formation. Organic nitrate formation from OH oxidation of n-alkenes and n-alkenes has been studied. Other VOCs, such as oxygenated or halogenated compounds could be a significant source of organic nitrates, but they have not been studied.
The organic nitrate formation yield from OH oxidation of halocarbons and oxygenated VOCs was studied in a photochemical reaction chamber. These formation yields were compared to those from n-alkanes in order to understand the effect of the functional groups on the organic nitrate yield. Furthermore, the individual yield for each methylene group was assessed in order to understand the importance of the position of the specific functional group in the formation of the nitrate. This, we hope, will help us develop a better understanding and maybe the capability to predict the organic nitrate yield of any VOC.