Gabrielle Petron

The impact of natural and anthropogenic hydrocarbons on the tropospheric budget of carbon monoxide

A method to quantify the relative contributions of surface sources and photochemical production of atmospheric carbon monoxide has been implemented in a three-dimensional chemical-transport model. The impact of biogenic and anthropogenic hydrocarbons has been calculated. The oxidation of isoprene contributes to about 10% of the global tropospheric burden of carbon monoxide, with a maximum contribution over southern America and Africa. Oxidation of methane and terpenes contribute to 28 and 2%, respectively, of the tropospheric burden of CO. The oxidation of the other hydrocarbons, which include ethane, propane, ethylene, propylene and the surrogate hydrocarbon representing other hydrocarbons results in 12% of the CO tropospheric burden, among which 69% results from the oxidation of hydrocarbons of biologic origin. The overall global CO yield from the oxidation of isoprene is estimated to be 23% on a carbon basis. Comparisons between model results and the few available observations of isoprene, terpenes and their oxidation products show that there is no evidence that the current global isoprene emissions proposed in the IGAC/GEIA emissions data base are substantially overestimated, as suggested by previous studies.

A three-dimensional study of the global CO budget

Abstract A global three-dimensional chemistry-transport model of the troposphere has been used to quantify the contribution of surface emissions, and of the oxidation of methane and non-methane hydrocarbons (NMHCs) to the distribution of carbon monoxide in the troposphere. A modeling technique has been developed, which allows the quantification of each component of the CO budget, without altering the distributions of other tropospheric species such as the hydroxyl radical OH. The calculated CO concentration are compared with long-term surface data, and regional as well as global budgets are quantified. Simulations results show that, if the impact of surface industrial emissions affect mostly the northern hemisphere, biomass burning emissions have a significant impact at all latitudes.

Improved Mechanistic Understanding of Natural Gas Methane Emissions from Spatially Resolved Aircraft Measurements

Divergence in recent oil and gas related methane emission estimates between aircraft studies (basin total for a midday window) and emissions inventories (annualized regional and national statistics) indicate the need for better understanding the experimental design, including temporal and spatial alignment and interpretation of results. Our aircraft-based methane emission estimates in a major U.S. shale gas basin resolved from west to east show (i) similar spatial distributions for 2 days, (ii) strong spatial correlations with reported NG production (R2 = 0.75) and active gas well pad count (R2 = 0.81), and (iii) 2× higher emissions in the western half (normalized by gas production) despite relatively homogeneous dry gas and well characteristics. Operator reported hourly activity data show that midday episodic emissions from manual liquid unloadings (a routine operation in this basin and elsewhere) could explain ∼1/3 of the total emissions detected midday by the aircraft and ∼2/3 of the west-east difference in emissions. The 22% emission difference between both days further emphasizes that episodic sources can substantially impact midday methane emissions and that aircraft may detect daily peak emissions rather than daily averages that are generally employed in emissions inventories. While the aircraft approach is valid, quantitative, and independent, our study sheds new light on the interpretation of previous basin scale aircraft studies, and provides an improved mechanistic understanding of oil and gas related methane emissions.

Data Assimilation and Inverse Methods

In the previous chapter we reviewed the principal methods of observations of atmospheric chemical constituents and showed how they can be used in relatively simple models, often 2-dimensional, to provide constraints on emission estimates. We will now discuss how these observations can be used in conjunction with more complex 3-dimensional chemical transport models to yield useful knowledge about surface emissions and the chemical state of the atmosphere by employing methods based on estimation theory, called inverse method and data assimilation. Although there is a rich history of application of this theory in other fields, such as meteorology, seismology, and remote sensing, it is only recently that data assimilation and inverse techniques have been developed to address atmospheric constituent problems.