Thursday, June 17, 2010
As I have mentioned earlier, the DOE G-1 aircraft typically flies around 1000-3000 ft above ground level, and samples aerosols within the boundary layer, as close as possible to the emission sources on the ground. We also frequently sample at increasing altitudes, up to 8000 ft, to characterize the vertical distribution of aerosols. This sampling strategy provides valuable data on aerosol size, composition, and its climate-affecting properties along horizontal and vertical lines, i.e., the path of the aircraft flight in the atmosphere.
To complement the in situ data obtained onboard the G-1, we are deploying the NASA B-200 King Air aircraft that typically flies at 28,000 ft, and carries specialized instruments capable of remotely sensing the scattering properties and shape of aerosols below it all the way to the ground.
The B-200 team is led by Dr. Richard Ferrare and Dr. Chris Hostetler of NASA's Langley Research Center. Their instrument, the High Spectral Resolution Lidar (HSRL), is installed in the belly of the aircraft, and it "looks" down to remotely sense the vertical distribution of aerosols as it flies around at 28,000 ft, often in sync with the G-1 flying the same pattern at 1000 ft. The results look like pretty "curtains" of color-coded properties of aerosols as shown in the picture.
The B-200 is also equipped with the Research Scanning Polarimeter (RSP), which provides an estimate of the optical properties of aerosols in the columns of air below the aircraft. The principal investigator of the RSP instrument is Dr. Brian Cairns at NASA's Goddard Institute of Space Studies.
It's been a pleasure to work with Rich Ferrare the past couple of weeks. He went back today as Chris Hostetler and Mike Obland replaced him. I also had the pleasure of making two new friends from NASA—Ray Rogers and Matteo Ottaviani, who gave me a nice tour of the B-200 aircraft the other day. Check out Matteo's blog: Who CARES? to see some stunning photos and videos and more information on NASA's participation in CARES.
Wednesday, June 16, 2010
The morning and afternoon flights yesterday, June 15, were quite successful. All instruments worked without any issues, the temperature inside the G-1 aircraft cabin remained comfortable throughout the flight, and the meteorological conditions were nearly ideal. The Sacramento plume was clearly "visible" from the measurements by different instruments onboard the G-1.
One of the key instruments used in characterizing the composition of aerosol particles is the Aerosol Mass Spectrometer (AMS) of Aerodyne Research, Inc. We have deployed three AMS units in CARES. The one on the G-1 aircraft belongs to the Environmental Molecular Sciences Laboratory (EMSL), a DOE national scientific user facility at PNNL. It is maintained by Dr. Liz Alexander and is being operated by Dr. John Shilling of PNNL for the CARES campaign.
The AMS unit deployed at the American River College site belongs to PNNL, and is being operated by Dr. Dr. Chen Song. Dr. Qi Zhang, Assistant Professor, UC Davis, and her post-doctoral research associate Ari Setyan are running another AMS unit at the Cool site. Special thanks are due to Drs. John Jayne, Ed Fortner, Tim Onasch, and Doug Worsnop of Aerodyne Research, Inc., for their efforts to ensure smooth operation of the AMS units during CARES.
The AMS measures the average composition of particles within certain size ranges, as well as the average composition of all the particles between about 60 and 600 nanometer diameters.
In addition to the AMS, we have also deployed a bulk aerosol composition measurement at each ground site and onboard the G-1 aircraft using the Particle-In-Liquid Sampler (PILS) system of Brechtel Manufacturing, Inc (BMI). Before the campaign began, Fred J. Brechtel of BMI trained Dan Cziczo, Mikhail Pekour, Chen Song, Danny Nelson, and Celine Kluzek of PNNL to operate the PILS system. It collects aerosol particles in the form of aqueous solution in small vials at pre-programmed time intervals - every hour at the ground sites and every three minutes on the G-1 aircraft. These samples are being analyzed by Qi Zhang's post-doctoral research associate, Dr. Yele Sun at UC Davis.
Fred Brechtel has also designed and manufactured a specialized a aerosol inlet system that carefully draws the ambient aerosols into the aircraft as it is moving at 100 meters per second.
Monday, June 14, 2010
Today it was distinctly hazier than it has been since we started the study. Hazy sky means more aerosol particles in the air. This is good news for us!
We are exactly half way through the study, and so far it has been pretty clean up here. We were therefore excited to see some hazy conditions develop in this area, especially to the west as shown in the "before" and "after" pictures I took from McClellan Airport. The G-1 aircraft flew close to the Bay Area to sample air pollution coming into the Central Valley and towards Sacramento. Art Sedlacek of Brookhaven National Laboratory took an aerial shot of a power plant along the Carquinez Strait. Hopefully, the hazy conditions around Sacramento will last for the rest of the study so we can contrast the observations from the first half with the second.
At the beginning of the campaign I had promised to introduce different research groups and their instruments that are part of the CARES study. I will start today with Dr. Tom Jobson, Associate Professor, and his graduate students Mike Erickson and Will Wallace from Washington State University, Pullman, WA.
Tom's group is deploying their Mobile Atmospheric Chemistry Laboratory (MACL) trailer, which houses a suite of instruments for field research on atmospheric aerosols. For the CARES project, they have configured the trailer to measure a variety of gaseous pollutants that are directly or indirectly responsible for secondary aerosol formation. These gases include nitrogen oxides (NOx), sulfur dioxide (SO2), ozone (O3), carbon monoxide (CO), and a variety of volatile and semi-volatile organic gases that are emitted from vehicle exhaust as well as trees. The instruments that measure the organic gases include the Proton Transfer Reaction Mass Spectrometer (PTR-MS) (PTR-MS) and the Gas Chromatography-Ion Trap Mass Spectrometer (GC-ITMS). The WSU trailer is part of the extensive suite of instruments at the American River College site.
Dr. Berk Knighton, Associate Research Professor, and his student Cody Floerchinger from Montana State University are also measuring organic trace gases with another PTR-MS instrument at the Cool site. Dr. Scott Herndon of Aerodyne Research, Inc., is also here to oversee the operation while Berk had to go back for a few days.
Particular emphasis is given to the measurement of volatile and semi-volatile organic gases, which upon oxidation form secondary organic aerosols. Measurement of aerosol composition at many places around the world has shown that organic compounds typically constitute between 20 and 90% of the total mass for aerosol particles smaller than 2.5 microns in diameter. However, significant uncertainties and knowledge gaps still exist in our ability to simulate the formation and evolution organic aerosols in a climate model.
As part of the CARES field campaign, we are trying to learn more about organic aerosol formation and their climate-affecting properties by measuring how organic gases and aerosols evolve in the Sacramento and Bay Area urban plumes as well as in the surrounding forested regions.
Sunday, June 13, 2010
On Friday, June 11, we had our first science meeting to review the data collected so far. Most of the participants attended the meeting while a few spent the day calibrating or fixing their instruments so that they were ready for the next day's aircraft missions. The meeting started at 3:00 PM and went on for 3 hours. This was the first time the aircraft and ground sites folks met each other since the campaign began, so everybody was eager to show their measurements as well as curious to see what others had observed so far. The goal was to make some sense of all the different measurements made at two ground sites and from two aircraft. The intense discussions often continue after hours over dinner.
The main story that is emerging so far is that the background air in the Central Valley surrounding the Sacramento area has been unusually clean since the campaign began June 2. However, there is evidence of enhanced concentrations of ultrafine aerosols, between 3 and 10 nanometers in diameter, in the Sacramento urban plume, and on some days the ultrafine aerosols are also observed in air outside the urban plume.
These findings were confirmed again on Saturday, June 12, when we conducted two aircraft missions south of Sacramento, in San Joaquin Valley. Along with the enhanced concentrations of ultrafine particles, we also see relatively larger, but still quite small, black carbon particles inside the Sacramento plume. Black carbon particles can absorb sunlight and therefore tend to warm the atmosphere. Also, their absorption efficiency increases when they get coated with other non-absorbing substances present in the urban plume or from natural sources. As part of the CARES objectives, we will investigate these mechanisms once all the data are collected and analyzed.
Today was the hottest day here since the campaign began. It reached 100° F (38° C) by 4 PM. It was not a problem because we weren't flying today. Tomorrow is going to be equally hot, so we will try to do only one flight in the morning and then get the aircraft back in the hangar before the mercury climbs high in the afternoon.