Project at a Glance

Title: AMAX-DOAS trace gas column observations from the research aircraft over California

Principal Investigator / Author(s): Volkamer, Rainer

Contractor: University of Colorado

Contract Number: 09-317

Research Program Area: Atmospheric Processes

Topic Areas: Chemistry & Reactivity, Field Studies


The CU Airborne MAX-DOAS instrument was deployed in California aboard the NOAA Twin Otter research aircraft during May 19-July 19, 2010. A total of 52 flights were carried out covering the entire state but with a particular focus over South Coast Air Basin (SCAB) and the Sacramento area. CU AMAX-DOAS measured horizontal and vertical distributions of nitrogen dioxide (NO2), formaldehyde (HCHO) and glyoxal (CHOCHO) during the campaign. Other instruments aboard the aircraft included NOAA TOPAZ lidar which measures vertical profiles of ozone (O3) and aerosols, NCAS Doppler lidar which measures wind profiles, two radiometers to measure surface albedo, a radiometer to measure surface temperature, an in-situ O3 monitor and temperature sensors.

The footprint of CU AMAX-DOAS measurements (~0.02 x 0.9 km2 while flying at 4 km AGL) is similar to the spatial resolution of atmospheric model predictions (4 x 4 km2), and our observations provide means to bridge between ground-based observations as part of measurement networks, Supersites, and satellites to improve atmospheric models used to manage air resources over California. Here, we start with an overview of the field deployment of the NOAA Twin Otter and then present various analyses of the data. Our analyses highlight the benefits of CU AMAX-DOAS observations for atmospheric model improvements, satellite retrievals and co-benefit of column/profile measurements of NO2, OVOCs, O3 and wind measurements aboard a research aircraft. We have further deployed two ground based MAXDOAS instruments at the CARB measurement station in Fontana Arrows, and at the Caltech Supersite, and relocated one of the instruments for a period of time to the T1 site in Cool downwind of Sacramento. We have used these ground-based column observations to evaluate the uncertainty of mobile NO2 VCD measurements from the aircraft during frequent overpasses with the aircraft. The agreement is found to be excellent ( < 7% error), and shows the data is useful to evaluate NOx emissions with high accuracy. Our further analysis of the NOx emissions from urban areas shows excellent agreement with the CARB 2010 emission inventory (within 30%). NOx emission flux calculations over Bakersfield area also gave similar agreement. However, emissions from oil and gas operations were found to be missing in the emission inventory. These emissions also lead to significant O3 production in the Bakersfield area.

We also present the assessment of the NASA OMI satellite NO2 data over California during summer months. We show that uncertain vertical distributions and high surface albedo lead to compensating uncertainty in the NASA OMI satellite NO2 product, which provides useful data over California during summer months to test atmospheric models over large spatial scale. We present new evidence that supports O3 formation chemistry being near the peak or on verge of transitioning to NOx limited conditions in the SCAB. Finally, we present case studies for HCHO and CHOCHO distributions in the SCAB and show that current atmospheric models significantly under predict these oxygenated VOCs (OVOC) with implications for O3 as well as secondary (inorganic and organic) aerosol formation.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

Stay involved, sign up with CARB's Research Email Distribution List