Defining Tropospheric Chemistry As A Heterogeneous Ensemble Of Reactive Air Parcels

Two major challenges in model-measurement comparisons have been: Which measurements are the most important to match? At what level do models need to simulate the variegated fine structures observed in trace gases and aerosols? This talk presents a novel approach for evaluating high-resolution global chemistry models (1/2 to 1 deg) that is integral to NASA's Atmospheric Tomography (ATom) mission. The approach seeks to develop a chemical climatology for tropospheric regions rather than just event-based testing of specific observations. It enables chemistry-climate models to be readily compared and more severely tested with observations. It uses the reactivity of air parcels (e.g., loss of methane, production and loss of ozone) to weight each parcel in terms of its importance in controlling the two most important chemically reactive greenhouse gases. It looks at the entire statistical distribution of air parcels in terms of a chemical phase space for those species that control the reactivity (e.g., O3, H2O, CH4, CO, NOx, HNO3, HNO4, PAN, CH3NO3, HCHO, HOOH, CH3OOH, C2H6, C3H6O, and other VOCs when present in sufficiently large abundances). It builds statistics of chemically extreme air parcels such as pollution layers to determine if a model failure to match such cases affects the overall reactivity of the region. This approach was designed for the ATom in situ measurements using the DC-8 to slice through the middle of the Pacific and Atlantic Ocean basins each season. The ATom payload will measure the above key trace gases and many other gases and aerosols in every designated air parcel (i.e., 10-sec averages). The first ATom measurements will not be available until mid-2017 and this presentation shows how this climatology looks when sampled with different models. Six global chemistry models have simulated one day in August (no particular year), and we sample all six showing how the 2D probability density plots highlight different regions when weighted by chemical reactivity. These models pre-simulation of ATom provide a target for the ATom measurements. The models also enable us to estimate the representativeness of ATom's single tomographic slice down the ocean basins, and therefore just how well we can observationally determine this chemical climatology of the reactivity of the troposphere.