Tomoaki Tanaka

Two-Year Comparison of Airborne Measurements of CO 2 and CH 4 With GOSAT at Railroad Valley, Nevada

The Alpha Jet Atmospheric eXperiment (AJAX) is a project to measure the atmospheric profiles of greenhouse gases (GHGs) and ozone (O3) regularly over California and Nevada. Airborne instruments measuring GHGs and O3 are installed in a wing pod of an Alpha Jet aircraft and operated from the National Aeronautics and Space Administration Ames Research Center at Moffett Field, CA. The instruments yield precise and accurate in situ vertical profiles of atmospheric carbon dioxide (CO2), methane (CH4), and O3. Measurements of vertical profiles of GHGs and O3 over Railroad Valley, NV have been conducted directly under the Greenhouse gases Observing SATellite (GOSAT) over passes on a monthly basis as part of the AJAX project since June 2011. The purpose of this work is to calculate aircraft-based dry-air mole fractions of the GHGs for the validation of GOSAT data products. This study expands and improves our previous comparisons by evaluating three algorithms against 24 months of in situ data collected over a Gain-M target. We used three different algorithms: Atmospheric CO2 Observations from Space (ACOS v3.4r3), Remote Sensing of Greenhouse Gases for Carbon Cycle Modeling (RemoteC v2.3.5FP), and National Institute for Environmental Studies (NIES v2.11). We find that the CO2 average differences of ACOS and RemoteC from AJAX are 0.26% and 0.24%, respectively. The difference between NIES and AJAX is 0.96%, which is higher than that of ACOS and RemoteC. The CH4 average differences for RemoteC and NIES are 2.1% and 1.7%, respectively.

Investigating seasonal methane emissions in Northern California using airborne measurements and inverse modeling

Seasonal methane (CH4) emissions in northern California are evaluated during this study using airborne measurement data and inverse model simulations. This research applies Alpha Jet Atmospheric eXperiment (AJAX) measurements obtained during January – February 2013, July 2014, and October – November 2014 over the San Francisco Bay Area (SFBA) and northern San Joaquin Valley (SJV) in order to constrain seasonal CH4 emissions in northern California. The California Greenhouse Gas Emissions Measurement (CALGEM) a priori emission inventory was applied in conjunction with the Weather Research and Forecasting and Stochastic Time-Inverted Lagrangian Transport (WRF-STILT) model and inverse modeling techniques to optimize CH4 emissions. Comparing model-predicted CH4 mixing ratios with airborne measurements, we find substantial underestimates suggesting that CH4 emissions were likely larger than the year 2008 a priori CALGEM emission inventory in northern California. Using AJAX measurements to optimize a priori emissions resulted in CH4 flux estimates from the SFBA/SJV of 1.77u2009±u20090.41, 0.83u2009±u20090.31, and 1.06u2009±u20090.39 Tg yr-1 when using winter, summer, and fall flight data, respectively. Averaging seasonal a posteriori emission estimates (weighted by posterior uncertainties) results in SFBA/SJV annual CH4 emissions of 1.28u2009±u20090.38 Tg yr-1. A posteriori uncertainties are reduced more effectively in the SFBA/SJV region compared to state-wide values indicating that the airborne measurements are most sensitive to emissions in this region. A posteriori estimates during this study suggest that dairy livestock was the source with the largest increase relative to the a priori CALGEM emission inventory during all seasons.

An Assessment of Ground Level and Free Tropospheric Ozone Over California and Nevada

Increasing free tropospheric ozone (O3), combined with the high elevation and often deep boundary layers at western US surface stations, poses challenges in attaining the more stringent 70 ppb O3 National Ambient Air Quality Standard. As such, use of observational data to identify sources and mechanisms that contribute to surface O3 is increasingly important. This work analyzes surface and vertical O3 observations over California and Nevada from 1995 to 2015. Over this period, the number of high O3 events (95th percentile) at US EPA CASTNET sites has decreased during summer, as a result of decreasing US emissions. In contrast, an increase in springtime 5th percentile O3 indicates a general increase of baseline O3. During 2012 there was a peak in exceedances and in the average spring-summer O3 mixing ratios at CASTNET sites. GEOS-Chem results show that the surface O3 attributable to transport from the upper troposphere and stratosphere were increased in 2013 compared to 2012, highlighting the importance of measurements aloft. Vertical O3 measurements from aircraft, ozonesondes and lidar show distinct seasonal trends, with a high percentage of elevated O3 laminae (O3 >70 ppb, 3-8 km) during spring and summer. Analysis of the timing of high O3 surface events and correlation between surface and vertical O3 data is used to discuss varying sources of western US surface O3.