Thursday, June 10, 2010
The last two days have been pretty hectic. According to Jerome Fast's weather briefing, June 7, the wind pattern on June 8 was expected to transport the Sacramento urban plume to the northeast by late afternoon. This is the type of flow pattern we were waiting for.
We conducted two flights that day: one in the morning from 9:00 AM - noon and another in the afternoon from 3:30 PM - 6:30 PM. The morning flight was designed to sample the freshly emitted pollutants over the Sacramento urban area, while the afternoon flight was designed to sample the aged pollution over the Cool site.
Hot and sunny days during summer in Sacramento area are conducive to the upslope mountain flows we are interested in, but high temperatures are also of great concern inside the aircraft. Many instruments (and their operators) onboard the G-1 will show signs of trouble when the cabin temperature increases above 100° F (38° C). The AAF crew installed an air conditioner, rigged up some ducting, and took several other measures to keep the aircraft cool.
Unfortunately, the compressor itself failed after the first flight on June 8. Still, the crew decided to go for the afternoon flight since the ambient temperature was cooler than the previous day. The cabin temperature remained under control for the most part of the flight. Some instruments had to be shut off toward the end to prevent any potential damage.
June 9 was declared a down day, so the crew could replace the compressor and fix a few other things before the really hot days arrive next week.
The air conditioner was up and running again this morning, and we did a flight in the afternoon.
Tomorrow we will have our first science meeting to review the data collected by different instruments at both the ground sites and onboard the two aircraft over the past week.
Monday, June 7, 2010
Folks working at the Cool site, up in the foothills of the Sierra Nevada Mountains, have the pleasure of driving back and forth everyday on the scenic Route 49 between Auburn and Cool in the El Dorado County - the home of the world-shaking Gold Rush of 1849.
I visited the Cool site today to check on a few things, and stopped on the way to appreciate the natural beauty of the area. The 7 mile long winding road cuts the Middle Fork of the American River, which originates in the high Sierra Nevada just west of Lake Tahoe, in the Tahoe and El Dorado National Forests. An added attraction along this route is the view of the Foresthill Bridge, which is the tallest bridge in California, and the 3rd tallest bridge of its kind in the United States. There is a tremendous diversity of flora and fauna in this region as well. We have spotted a few birds and insects at the site, and Berk Knighton's graduate student, Cody Floerchinger of Montana State University, has seen snakes in the area several times already. I am hoping to see at least one in the coming days if I am lucky.
The mixed-evergreen coniferous forests in the Sierra Nevada Mountains are also a rich source of volatile organic compounds such as isoprene, methyl butenol, and monoterpenes. These compounds are emitted from tree leaves as part of natural processes, and their emission rate increases when it is hot and sunny. Once in the air, these compounds can get oxidized by reacting with ozone and other oxidants formed in the presence of sunlight to form low volatility compounds, which can either nucleate to form very small (ultrafine) organic particles or condense upon pre-existing particles.
Since these particles are formed from oxidation of organic gases, they are called secondary organic aerosols (SOA), as opposed to primary organic aerosols (POA), which are directly emitted from vehicle exhaust or meat cooking. As part of the CARES field study, we are interested in learning more about how the Sacramento urban air pollution interacts with natural emissions of organic gases, and thereby affects the natural processes of secondary organic aerosol formation in forested areas as well as in the urban plume.
Sunday, June 6, 2010
The day started very early for the aircraft teams and the weather balloon launch teams at both the ground sites. The aircraft ground support crew and the instrument PIs have to start preparing the aircraft and the instruments at least 3 hours before takeoff. On a flight day, five weather balloons are launched, one every three hours, starting at 7 AM. The NASA B-200 took off at 9:00 AM while the DOE G-1 took off at 10:40 AM. Both aircraft landed after sampling over the urban area for about 3 hours. The G-1 crew grabbed a quick bite, refueled, and jumped back on the plane for another takeoff at 3:30 PM.
Thanks to Jason Tomlinson, we are now able to download selected data from the G-1 in real time so that folks on the ground can look at what was being measured by the G-1 while it is in flight.
A quick look at the morning flight's data confirmed what we have been seeing at both the ground sites the past few days—very clean air, except for a huge concentration of very small particles (between 3 and 12 nanometers) within and outside the Sacramento urban area. NASA B-200's data also support this finding on a slightly larger scale. While a careful analysis of all the data is needed to understand the source(s) of these particles, the working hypothesis is that these ultrafine particles are formed from nucleation of sulfuric acid vapors, which grow bigger by condensation of organic vapors from natural sources (trees and other vegetation).
In the afternoon flight, the concentrations of these very small particles were 2-3 times lower compared to the morning flight. This can occur due to a number of processes, such as coagulation (i.e., two or more particles colliding and sticking with each other), condensational growth (i.e., additional vapors glomming onto them), and dilution as the turbulent boundary layer grows deeper in the afternoon. The boundary layer is the turbulent layer of air close to the ground, where air pollutants mix up during the day. It starts out very shallow (less than 100 meters) early in the morning and can grow 1 to 2 km high (or even higher) throughout the day as the sun heats up the ground and produces air thermals.
High afternoon temperatures can also cause the aircraft cabin to heat up a little bit too much, which can cause many instruments to malfunction. We had a bit of this issue today as the afternoon temperature on the ground reached about 90° F (32° C). We have decided to address the heat issues tomorrow and be prepared for even warmer weather in the coming days.
Saturday, June 5, 2010
The CARES media event yesterday went quite well, thanks to the meticulous preparations by PNNL's Mary Beckman, Media Relations, and Lynne Roeder, Communications Specialist, and the rest of the outreach team—Kathryn Lang, Kimberly Tebrugge, and Dana Dupont for their help in planning the event. It started at the American River College site at 11 am and continued on to the McClellan Airport until about 2 pm. A number of reporters from various news media interviewed several of the CARES team members and took tours to view the instrumented trailers and the G-1 aircraft.
I would like to thank our invited guests Dr. Bart Croes, Division Chief of California Air Resources Board (CARB) and Dr. Eileen McCauley, Manager of the Atmospheric Processes Research Section, for attending the event and for their valuable assistance during the planning of CARES. A couple of interested chemistry professors from American River College and the Assistant Dean of Science and Engineering, Dr. Derrick Booth, also graced the occasion.
The reporters seemed to be quite enthusiastic about our work. They asked a lot of questions of about the scientific objectives of the CARES field study, data collection methods and instrumentation, and what all of this means to the general public—why should they care about CARES? Check out the article in the Sacramento Bee newspaper and Fox 40 Sacramento News video—I think they did a pretty good job in getting the main points across.
The aircraft team was busy preparing the instruments today in anticipation for a couple of flights tomorrow. The weather forecast calls for a warm day and the wind pattern looks favorable for the transport of the Sacramento urban plume to the west or northwest. It's going to be a long day.