Spatio-Temporal Variability of Atmospheric CO2 as Observed from In-Situ Measurements over North America during NASA Field Campaigns (2004-2008)

Regional-scale measurements were made over the eastern United States (Intercontinental Chemical Transport Experiment - North America (INTEX-NA), summer 2004); Mexico (Megacity Initiative: Local and Global Research Observations (MILAGRO), March 2006); the eastern North Pacific and Alaska (INTEX-B May 2006); and the Canadian Arctic (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS), spring and summer 2008). For these field campaigns, instrumentation for the in situ measurement of CO2 was integrated on the NASA DC-8 research aircraft providing high-resolution (1 second) data traceable to the WMO CO2 mole fraction scale. These observations provide unique and definitive data sets via their intermediate-scale coverage and frequent vertical profiles (0.1 - 12 km) for examining the variability CO2 exhibits above the Earth s surface. A bottom-up anthropogenic CO2 emissions inventory (1deg 1deg) and processing methodology has also been developed for North America in support of these airborne science missions. In this presentation, the spatio-temporal distributions of CO2 and CO column values derived from the campaign measurements will be examined in conjunction with the emissions inventory and transport histories to aid in the interpretation of the CO2 observations

Observations of convective and dynamical instabilities in tropopause folds and their contribution to stratosphere-troposphere exchange

With aircraft-mounted in situ and remote sensing instruments for dynamical, thermal, and chemical measurements we studied two cases of tropopause folding. In both folds we found Kelvin-Helmholtz billows with horizontal wavelength of ∼900 m and thickness of ∼120 m. In one case the instability was effectively mixing the bottomside of the fold, leading to the transfer of stratospheric air into the troposphere. Also, we discovered in both cases small-scale secondary ozone maxima shortly after the aircraft ascended past the topside of the fold that corresponded to regions of convective instability. We interpreted this phenomenon as convectively breaking gravity waves. Therefore we posit that convectively breaking gravity waves acting on tropopause folds must be added to the list of important irreversible mixing mechanisms leading to stratosphere-troposphere exchange.United States. National Aeronautics and Space Administration (Grant NAG2-1105)United States. National Aeronautics and Space Administration (Grant NAGl-1758)United States. National Aeronautics and Space Administration (Grant NAGl-1901

Sources of upper tropospheric HO\u3csub\u3e\u3cem\u3ex\u3c/em\u3e\u3c/sub\u3e over the South Pacific Convergence Zone: A case study

A zero‐dimensional (0‐D) model has been applied to study the sources of hydrogen oxide radicals (HOx = HO2 + OH) in the tropical upper troposphere during the Pacific Exploratory Mission in the tropics (PEM‐Tropics B) aircraft mission over the South Pacific in March–April 1999. Observations made across the Southern Pacific Convergence Zone (SPCZ) and the southern branch of the Intertropical Convergence Zone (ITCZ) provided the opportunity to contrast the relative contributions of different sources of HOx, in a nitrogen oxide radical (NOx)‐limited regime, in relatively pristine tropical air. The primary sources of HOx vary significantly along the flight track, in correlation with the supply of water vapor. The latitudinal variation of HOx sources is found to be controlled also by the levels of NOx and primary HOx production rates P(HOx). Budget calculations in the 8‐ to 12‐km altitude range show that the reaction O(1D) + H2O is a major HOx source in the cloud region traversed by the aircraft, including SPCZ and the southern branch of the ITCZ. Production from acetone becomes significant in drier region south of 20°S and can become dominant where water vapor mixing ratios lie under 200 ppmv. Over the SPCZ region, in the cloud outflow, CH3 OOH transported by convection accounts for 22% to 64% of the total primary source. Oxidation of methane amplifies the primary HOx source by 1–1.8 in the dry regions

Asian outflow and trans-Pacific transport of carbon monoxide and ozone pollution: An integrated satellite, aircraft, and model perspective

Satellite observations of carbon monoxide (CO) from the Measurements of Pollution in the Troposphere (MOPITT) instrument are combined with measurements from the Transport and Chemical Evolution Over the Pacific (TRACE-P) aircraft mission over the northwest Pacific and with a global three-dimensional chemical transport model (GEOS-CHEM) to quantify Asian pollution outflow and its trans-Pacific transport during spring 2001. Global CO column distributions in MOPITT and GEOS-CHEM are highly correlated (R2 = 0.87), with no significant model bias. The largest regional bias is over Southeast Asia, where the model is 18% too high. A 60% decrease of regional biomass burning emissions in the model (to 39 Tg yr−1) would correct the discrepancy; this result is consistent with TRACE-P observations. MOPITT and TRACE-P also give consistent constraints on the Chinese source of CO from fuel combustion (181 Tg CO yr−1). Four major events of trans-Pacific transport of Asian pollution in spring 2001 were seen by MOPITT, in situ platforms, and GEOS-CHEM. One of them was sampled by TRACE-P (26–27 February) as a succession of pollution layers over the northeast Pacific. These layers all originated from one single event of Asian outflow that split into northern and southern plumes over the central Pacific. The northern plume (sampled at 6–8 km off California) had no ozone enhancement. The southern subsiding plume (sampled at 2–4 km west of Hawaii) contained a 8–17 ppbv ozone enhancement, driven by decomposition of peroxyacetylnitrate (PAN) to nitrogen oxides (NOx). This result suggests that PAN decomposition in trans-Pacific pollution plumes subsiding over the United States could lead to significant enhancements of surface ozone

Prevalence of ice-supersaturated regions in the upper troposphere : implications for optically thin ice cloud formation

In situ measurements of water vapor and temperature from recent aircraft campaigns have provided evidence that the upper troposphere is frequently supersaturated with respect to ice. The peak relative humidities with respect to ice (RHI) occasionally approached water saturation at temperatures ranging from -40°C to -70°C in each of the campaigns. The occurrence frequency of ice supersaturation ranged from about 20% to 45%. Even on flight segments when no ice crystals were detected, ice supersaturation was measured about 5-20% of the time. A numerical cloud model is used to simulate the formation of optically thin, low ice number density cirrus clouds in these supersaturated regions. The potential for scavenging of ice nuclei (IN) by these clouds is evaluated. The simulations suggest that if less than about 5 x 10¯³ to 2 x 10¯² cm¯³ ice nuclei are present when these supersaturations are generated, then the cirrus formed should be subvisible. These low ice number density clouds scavenge the IN from the supersaturated layer, but the crystals sediment out too rapidly to prevent buildup of high supersaturations. If higher numbers of' ice nuclei are present, then the clouds that form are visible and deposition growth of the ice crystals reduces the RHI down to near 100%. Even if no ice clouds form increasing the RHI from 100% to 150% between 10 and 10.5 km results in a decrease in outgoing longwave radiative flux at the top of the atmosphere of about 8 W m¯². If 0.02-0.1 cm¯³ IN are present, the resulting cloud radiative forcing reduces the net radiative flux several watts per square meter further. Given the high frequency of supersaturated regions without optically thick clouds in the upper troposphere, there is a potential for a climatically important class of optically thin cirrus with relatively low ice crystal number densities. The optical properties of these clouds will depend very strongly on the abundance of ice nuclei in the upper troposphere

Large-scale ozone and aerosol distributions, air mass characteristics, and ozone fluxes over the western Pacific Ocean in late winter/early spring

Large‐scale measurements of ozone (O3) and aerosol distributions were made from the NASA DC‐8 aircraft during the Transport and Chemical Evolution over the Pacific (TRACE‐P) field experiment conducted in February–April 2001. Remote measurements were made with an airborne lidar to provide O3 and multiple‐wavelength aerosol backscatter profiles from near the surface to above the tropopause along the flight track. In situ measurements of O3, aerosols, and a wide range of trace gases were made onboard the DC‐8. Five‐day backward trajectories were used in conjunction with the O3 and aerosol distributions on each flight to indicate the possible origin of observed air masses, such as from biomass burning regions, continental pollution, desert regions, and oceanic regions. Average latitudinal O3 and aerosol scattering ratio distributions were derived from all flights west of 150°E, and these distributions showed the average latitude and altitude dependence of different dynamical and chemical processes in determining the atmospheric composition over the western Pacific. TRACE‐P (TP) showed an increase in the average latitudinal distributions of both O3 and aerosols compared to PEM‐West B (PWB), which was conducted in February–March 1994. O3, aerosol, and potential vorticity levels were used to identify nine air mass types and quantify their frequency of occurrence as a function of altitude. This paper discusses the characteristics of the different air mass types encountered during TP and compares them to PWB. These results confirmed that most of the O3 increase in TP was due to photochemistry. The average latitudinal eastward O3 flux in the western Pacific during TP was found to peak near 32°N with a total average O3 flux between 14 and 46°N of 5.2 Tg/day. The eastward total CO flux was calculated to be 2.2 Tg‐C/day with ∼6% estimated from Asia. The Asian flux of CO2 and CH4 was estimated at 4.9 and 0.06 Tg‐C/day

Direct Measurements of the Convective Recycling of the Upper Troposphere

We present a statistical representation of the aggregate effects of deep convection on the chemistry and dynamics of the Upper Troposphere (UT) based on direct aircraft observations of the chemical composition of the UT over the Eastern United States and Canada during summer. These measurements provide new and unique observational constraints on the chemistry occurring downwind of convection and the rate at which air in the UT is recycled, previously only the province of model analyses. These results provide quantitative measures that can be used to evaluate global climate and chemistry models

Airborne Observations of the Spatial and Temporal Variability of Tropospheric Carbon Dioxide during the INTEX-B Campaign

The Intercontinental Chemical Transport Experiment-North America (INTEX-NA) is an international field campaign envisioned to investigate the transport and transformation of gases and aerosols on transcontinental/intercontinental scales and assess their impact on air quality and climate. Phase B (INTEX-B) of the mission was conducted during a 10- week period from March 1 to May 15, 2006 and focused initially on pollution outflow from the Mexico City Metropolitan Area, later addressing the transport of pollution from Asia to North America during springtime meteorological conditions. During the deployment, fast-response (1-s resolution) CO2 measurements were recorded aboard the NASA DC-8 providing valuable regional-scale information on carbon sources and sinks over sparsely sampled areas of North America and adjacent ocean basins. When coupled with the enormously sophisticated chemistry payload on the DC-8, these measurements collectively afford extremely powerful multi-tracer constraints for carbon source/sink attribution. Preliminary examination of the two data sets from the INTEX-B campaign, acquired one month apart, reveals not only the influence of the CO2 seasonal cycle, but also the preponderance of human population and industrial activity in the northern hemisphere. In this presentation, a synergy of the ensemble of airborne and surface observations, bottomup emission inventories, as well as transport history are invoked in a GIS framework to elucidate the source/sink processes reflected in the observations. The airborne CO2 data, along with simultaneous surface measurements (e.g. NOAA ESRL), are examined to establish the vertical distribution and variability of CO2 as a function of location. The role of localized sources, long-range transport, the biosphere, stratospheric exchange, and dynamical processes on the CO2 spatial variability observed throughout the tropospheric column will be discussed