Distributions of Nonmethane Hydrocarbons and Oxygenated VOCs and Their Contribution to Chemical Reactivity and HOx Production in the Most Remote Troposphere during the NASA Atmospheric Tomography (ATom) Experiment

Volatile Organic Compounds (VOCs) play an important role in tropospheric chemistry and ozone formation. A primary sink for VOCs is through reaction with the hydroxyl radical (OH) and as such VOCs can strongly impact the OH budget. VOCs are emitted from vegetation, biomass burning and anthropogenic sources, including oil and gas extraction activities. Many VOCs are also formed in chemical reactions in the atmosphere. Distributions of non-methane hydrocarbons (NMHCs) and oxygenated volatile organic compounds (OVOCs) are presented from both the ATom-1 and ATom-2 deployments, which were conducted in different seasons, and comparisons between the two are made. These species are important ozone precursors and influence the oxidative capacity of the troposphere. The OH reactivity, a measure of the chemical reactivity of the atmosphere, is calculated for ATom-1 and ATom-2 as a function of altitude for data obtained in the most remote troposphere, and the overall contribution of VOCs to the total reactivity is determined. Sources of OH also need to be understood. The primary source of OH in the lower and mid-troposphere is the reaction of O(¹D) with water but as water vapor mixing ratios decrease with altitude this source becomes less important and other sources such as OVOCs become more important. We calculate the HO_x production from OVOC experimental data and use the CAM-chem model to compare measured with modeled HO_x produced from the OVOCs and other important HO_x precursors.