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On The Road Again...This Time, It's For Air Quality Testing

June 24, 2014

“Have idea, will travel” … while it’s not Drexel’s official slogan (yet) you could be forgiven if you think so. Over the last few years it seems as though research-on-wheels has become one of the university’s specialties. Add air quality to a list of mobile labs that already includes arts education and autism testing. Whether it’s in the spirit of Drexel’s community outreach mission or just an excuse for a creative paint job, students and faculty are packing their projects into a van and taking their brainpower to the people.

The latest iteration comes courtesy of a senior design project by students in the College of Engineering’s Department of Civil, Architectural and Environmental Engineering and the Drexel Air Resource and Research Laboratory (DARRL), who wanted to come up with an efficient way to perform air quality measurements through a cross section of Philadelphia and characterize emissions from individual sources.

“Cities like Philadelphia have a network of fixed air pollution monitors that track our air quality for regulatory purposes,” said Peter DeCarlo, PhD, an assistant professor in the College of Engineering and the group’s advisor. “These sites are expensive to run and maintain, so there is a limit to the number of sites that can be supported. A mobile measurement facility allows us to take our measurements anywhere, and characterize air quality and emissions from facilities at a neighborhood to city scale, complementing the fixed site monitors run by the city.”

Air quality is currently monitored by 10 field stations operated by the Philadelphia Air Management Services, and regionally, air quality is monitored by the Pennsylvania Department of Environmental Protection. These sites are located strategically throughout the city and region, and provide broad characterization of the Philadelphia area’s air quality every day of the year, something that can’t be done with a mobile facility. Daily air quality forecasts as well as current conditions for the city are available online.

To demonstrate the utility of a mobile monitoring vehicle a pilot scale setup was put together based on the seniors’ conceptual design. A 1990s, 12-passenger Ford van owned by the CAEE department -for field trips and transporting equipment- served as the wheels of the operation. Selected for its size and a roof design that allows for easily mounting test equipment, the van evolved into a modified mobile laboratory during the spring term.

The team equipped its lab-on-wheels with inlet tubing – for measuring particulates and non-reactive gas phase pollutants a set of three lengths of half-inch stainless steel tubing clamped to the edge of the roof that acts as a giant straw for sucking up air samples. For measuring reactive pollutants, quarter-inch Teflon tubing was also mounted on the roof.

These inlets collect ambient air from in front of the vehicle and are connected to a rack of instruments mounted inside the van via flexible tubing at the rear of the vehicle. The stainless steel and Teflon sampling tubing protrudes far enough from the van so that its own exhaust emissions don’t inadvertently skew the measurements being taken.

The air intake scoops up its sample continuously and the instruments instantaneously report concentrations of carbon dioxide, ozone and particulate matter. They are also able to count the total number of particulates in the sample. This process lets the team gather real-time data while driving across the city. A Globalsat GPS receiver is used to continuously record their every position throughout the city while sampling. 

The data is cross-referenced with climate measurements –including wind speed and direction, temperature, relative humidity and rain intensity- recorded by a weather station on Drexel’s campus. These are all atmospheric conditions that can affect air quality –for example, a hot, sunny day provides the necessary conditions for levels of ozone to build up in the air – and therefore must be accounted for when processing the data.

Sampling on the road is not without its challenges, however. It requires careful and detailed note-taking and a reliable navigator. Observations must be recorded constantly so there is a way to account for fluctuations in data. Things like getting stuck in a traffic jam, driving behind a diesel-fueled tractor trailer or even passing under a bridge will cause levels to spike –and it’s important to understand their correlation with these common traffic phenomena, or particularly poorly maintained vehicles.

M3 hit the road this spring for a test run –a three-hour tour that covered about 40 miles through much of Center City and South Philadelphia.

“We wanted to test in areas where you don’t normally think air quality would be an issue, like at a Phillies game where there’s increased car traffic and a lot of tailgating,” said Bonnie Vu a member of the team. “And of course, we wanted to test around residential areas that are close to highways and industrial facilities like the refinery by the Platt Bridge and up in Port Richmond.”

While the data from the initial test runs and additional mobile sampling near Bartram’s Gardens in Southwest Philadelphia, and Port Richmond is still being analyzed, the team was successful in demonstrating the accuracy, ease of sampling and affordability of a mobile monitoring unit.

Essentially the students have also shown that a system like M3 could be a viable option to complement the stationary monitoring centers. The group estimates that, within six years, the vehicle would pay for itself in savings from the labor costs associated with the additional testing necessary to monitor quality throughout the city.

The team next hopes to improve the system by adding backup power supplies, installing equipment to allow for sampling on rainy days and mounting a cyclone separator unit to keep large dust particles out of the instruments.

Long-term plans include upgrading to a newer sampling vehicle, installing a Vaisala weather station to make local meteorological measurements and adding instrumentation to record levels of other air contaminants specific to urban environments.

Members of the Drexel Air Resources Research Laboratory will continue to collect samples over a broader area of the city and will use the lessons learned from the initial sampling runs to perfect measurement techniques.