Wednesday, June 23, 2010
Today we observed the highest ozone levels—nearly 90 parts per billion—in this area since the campaign started. Ground-level ozone is one of the many air pollutants that are regulated by the Environmental Protection Agency (EPA) in the US. Breathing air containing ozone can decrease lung function, aggravate asthma symptoms, or cause other respiratory illnesses. Exposure to high levels of ozone may also contribute to premature death, especially in people with heart and lung disease, and it can harm sensitive vegetation and ecosystems as well. The current 8-hour average National Ambient Air Quality Standard (NAAQS) for ground-level ozone is 75 parts per billion.
Ozone is not emitted directly into the air. It is formed by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents are some of the major sources of NOx and VOCs.
The chemical reactions that form ozone are also directly or indirectly responsible for forming secondary aerosols such as sulfate, nitrate, and a variety of organic compounds. When breathed in, these small aerosol particles can reach into the deepest regions of the lungs and further aggravate asthma and respiratory conditions. Aerosol particles are therefore also regulated by the EPA, and the current 24-hour average standard for particles smaller than 2.5 microns in diameter is 35 micrograms per cubic meter.
These aerosol particles are also the main cause of haze and visibility degradation, and they play a significant role in climate modification due to increased scattering and/or absorption of sunlight. Increased concentrations of aerosol particles can also modify cloud properties and affect rainfall patterns in a highly polluted region. We have deployed a number of instruments in CARES that measure the optical (light scattering and absorption) and cloud formation properties of aerosols.
Dr. Patrick Arnott, Associate Professor, University of Nevada, Reno, and his graduate student Madhu Gyawali, along with Dr. Manvendra Dubey of Los Alamos National Laboratory and his post-doctoral research associate Dr. Brad Flowers have deployed instruments called the Photo-Acoustic Soot Spectrometer at the ground sites and onboard the G-1 aircraft to measure scattering and absorption of light by black carbon present in vehicle exhaust or biomass burning.
Dr. Dean Atkinson, Associate Professor, Portland State University, and his graduate student Jimmy Radney have deployed another instrument called the Cavity Ring-Down (CRD) spectrometer that also measures the optical properties of aerosols by a different technique. Dr. Chris Cappa, Assistant Professor at University of California, Davis, and his graduate student Kati Kolesar have also deployed a CRD instrument at the American River College site.
Dr. Mikhail Pekour and Dr. Larry Berg of Pacific Northwest National Laboratory have deployed yet another set of instruments called the Particle Soot Absorption Photometer (PSAP) and nephelometer, which measure light absorption and scattering, respectively. It is important to measure these critical climate-affecting aerosol properties by different techniques to increase our confidence in our results.
Monday, June 21, 2010
Yesterday (Sunday, June 20) was a hard down day for the aircraft folks, which means the pilots, support crew, and instrument scientists get the day off. They are not supposed to show up for work at all. I took that opportunity to have another science meeting to review and discuss the data collected so far.
The instruments I'd like to highlight today are the trace gas analyzers of Dr. Stephen Springston, Brookhaven National Laboratory (BNL). Stephen has more than 20 years of experience measuring trace pollutant gases, including oxides of nitrogen, ozone, sulfur dioxide, and carbon monoxide onboard the G-1 aircraft.
Nitric oxide, nitrogen dioxide, and carbon monoxide are formed from various combustion processes, and they are typically present in vehicle exhaust and power plant emissions. Sulfur dioxide is usually present in coal-fired power plant plumes and certain industrial emissions. In contrast, ozone is a "secondary" chemical, meaning it is formed in the atmosphere in the presence of sunlight, nitrogen oxides, and reactive organic gases.
Stephen's colleague Dr. Art Sedlacek of BNL has deployed a relatively new instrument called the Single Particle Soot Photometer (SP2), which measures black carbon particles that are also invariably present in vehicle exhaust as well as biomass burning (e.g., forest fires, agricultural burning) emissions.
The SP2 estimates black carbon mass in individual particles by heating them with a laser and measuring the intensity of the incandescence light at the color temperature specific to black carbon. The SP2 instrument is commercially available from Droplet Measurement Technologies (DMT), and Dr. Subramanian of DMT is also participating in CARES, operating an SP2 instrument at each ground site. Depending on the level of pollution, this instrument can produce up to 100 GB data per day!
Dr. Gunnar Senum of BNL, who's an expert in measuring aerosol and cloud droplet size distributions, recently joined us to relieve Stephen, and he will take turns with Art to operate several instruments on the G-1.
Dr. Jian Wang of BNL is also an expert in measuring aerosol size distributions. He has invented a new instrument called the Fast Integrated Mobility Spectrometer (FIMS) that measures the size distribution of aerosol particles between 30 and 100 nanometers every second. That's pretty fast! We have deployed FIMS on the G-1 for the CARES project to measure the size distributions of these very small particles at unprecedented speed and accuracy so that we can see how fast they grow due to "aging." Jian's post-doctoral research associate Dr. Chongai Kuang of BNL arrived here yesterday to assist with the FIMS measurements.
John Hubbe of PNNL is the aircraft "Payload Master," who is responsible for the overall layout of the payload, power supply, and operation of several instruments during flights.
Lastly, I'd like to thank Dr. Larry Kleinman of BNL for diligently going through all the data from various instruments to make sure they make sense. Larry's experience and mentorship has been absolutely invaluable!
More instruments and scientists tomorrow . . .
Saturday, June 19, 2010
We were scheduled to carry out two flights today, but some trouble with the power generator on the G-1 aircraft forced us to scrub the morning flight. Mechanic Gene Dukes quickly fixed the generator, and the aircraft was ready to fly again by noon.
AAF Technical Director Dr. Beat Schmid went back home a couple of days ago, and Deputy Technical Director Dr. Jennifer Comstock is here in his place. AAF Operations Lead Jason Tomlinson also went back home, and deserves a much needed break from the non-stop work the past several weeks. Thanks to both Beat and Jason for their hard work, and a warm welcome to Jennifer! We are now exactly two-thirds of the way through the study, with nine more days to go. There's still a lot of flying to be done and more data to be collected before we can all go home.
The data collected so far has shown some interesting results already. As I have mentioned earlier, one of the research issues we would like to address in CARES is the effect of different types of carbonaceous particles and their evolving compositions on their climate-affecting properties. Highly specialized instruments called "single-particle mass spectrometers" are needed to characterize and distinguish between different types of particles, from different sources, with different compositions and properties. We have deployed three such state-of-the-art single particle instruments in CARES.
The one deployed on the G-1 aircraft is called the "Aerosol Time-of-Flight Mass Spectrometer" or ATOFMS, which was developed under the leadership of Professor Kimberly Prather, University of California, San Diego. Dr. Prather's graduate students Kaitlyn Suski and Jack Cahill are operating the newest ATOFMS called "Shirley," who is smaller and faster than the previous generation. The single particle instrument deployed at the American River College site is called the "Single Particle Laser Ablation Time-of-flight Mass Spectrometer" or SPLAT II, which was developed by Dr. Alla Zelenyuk of PNNL. The SPLAT II belongs to the Environmental Molecular Sciences Laboratory, a national scientific user facility at PNNL. Dr. Zelenyuk's post-doctoral fellows Dr. Josef Beranek and Dr. Tim Vaden are operating the SPLAT II during CARES. The third instrument deployed at the Cool site is called the "Particle Analysis by Laser Mass Spectrometry" or PALMS, which is being operated by Dr. Dan Cziczo of PNNL.
Friday, June 18, 2010
One can never have enough aircraft and instruments! The NOAA Twin Otter, which is carrying out its missions as part of the CalNex field campaign, arrived at McClellan Airport on June 15, and will be collaborating with us until June 28. I like the Twin Otter. In a previous field study, a few years ago in Houston, TX, I had the pleasure of flying onboard another Twin Otter as the mission scientist. It's a highly maneuverable, versatile aircraft that can be flown at slow speeds, quite appropriate for carrying out air pollution sampling missions. The NOAA Twin Otter missions for CalNex are being led by Dr. Mike Hardesty, Dr. Christoph Senff, and Dr. Robert Banta of NOAA and Dr. Rainer Volkamer, Assistant Professor, University of Colorado, Boulder. Much like the NASA B-200, the NOAA Twin Otter carries several remote sensing instruments, including the downward looking ozone/aerosol and Doppler wind Lidars and an AMAX-DOAS system to measure various trace gases, aerosols, and wind profiles below the aircraft.
Now, whenever we have more than one aircraft carrying similar payloads, it is customary to carry out coordinated flight patterns to allow intercomparison of measurements from instruments on different aircraft. Such maneuvers need careful planning between the principal investigators and precise coordination between the pilots of all the aircraft involved in the intercomparison exercise. The proposed flight plan must meet all the safety requirements and must be approved by the Federal Aviation Administration (FAA).
Today we carried out such an intercomparison exercise between four aircraft—DOE G-1, NOAA WP-3, NOAA Twin Otter, and NASA B-200. The flight plan involved the DOE G-1 trailing behind the NOAA WP-3 by about 6 nautical miles at a speed of 190 nautical miles per hour at 1500 ft altitude, with the NASA B-200 and NOAA Twin Otter flying right above at 28000 and 6500 ft altitudes, respectively. As shown in the pictures, the G-1 (yellow trace) arrived at the agreed upon rendezvous point "34" near Fresno, CA, by 4:26 pm, and circled over it for about 35 minutes until the WP-3 (white trace) arrived there at 5:00 pm. The two aircraft then lined up as planned and flew close to each other to Bakersfield, sampling roughly the same air along the way. This strategy will allow us to compare the performance of instruments onboard the two aircraft, and thereby increase the confidence in our measurements. The NASA B-200 and NOAA Twin Otter flew over the same path at higher altitudes, so that their remote sensing instruments can provide the vertical context for the G-1 and WP-3 measurements.
Needless to say it was a pretty exciting day!