On a clear and crisp morning, with the sun beating down, Xenrong Ren and Phillip Stratton looked over plans for the day and fiddled with the gadgets installed in a black SUV parked outside the National Oceanic and Atmospheric Administration’s Center for Weather and Climate Prediction in College Park, Maryland.  

“Today we’re going to do a mobile measurement survey in Baltimore to look for major greenhouse gasses and some air pollutants in the area,” said Ren, a scientist at NOAA’s Air Resources Laboratory (ARL), which studies the lowest part of the atmosphere, called the boundary layer—the area where all species live and breathe. 

“But first we need to warm up the instruments, do calibration and testing to make sure everything works,” he said, pointing at the Chevy Suburban fitted with state-of-the-art sensors to track urban hotspots spewing heat-trapping greenhouse gases, including carbon dioxide and methane, which is 86 times more powerful than carbon dioxide in causing global warming over a 20-year period.

“We call it NOAA’s ARC,” Ren said of the instrumented “Air Resources Car” with a smirk visible behind his N-95 face mask. 

The sensors also trace air pollutants such as carbon monoxide (CO) and nitrogen oxides (NOx) emitted mostly from vehicular exhaust and contributing to ground-level ozone or smog. One sensor measures black carbon—a carcinogenic constituent of fine particulate matter (PM2.5) that also absorbs heat and contributes to climate change, emitted mostly by diesel trucks and often found on highways and in communities next to industrial facilities. 

Other instruments record wind speed and direction in real time, which determined the route Ren and Stratton would take on the drive around Washington, D.C.-Baltimore corridor. “It depends if we’re going to drive along north-south transects throughout the city or if we want to be driving east-west,” said Stratton, also a climate scientist and designated driver most of the days the duo is in action sniffing out methane leaks and tracking down sources of air pollution.

The antennas and sensors on the SUV sometimes prompt people to ask them what they are up to. “We tell them about the air quality as well as greenhouse gas emissions and how it relates to climate change. Most of the people are interested in knowing that,” Ren said. 

Some people think we’re doing something shady, given the unfamiliar look of the mobile lab, Stratton quipped.  

They avoid driving with the wind because the air currents would carry the plumes away, making it difficult to locate the source of emission. “We’re driving perpendicular to the wind speed as much as possible to catch the plumes close to the point sources,” Stratton said. 

The order of business on this day was to drive around Baltimore and survey the downtown area, pass by a wastewater treatment facility and a landfill site, and then make a pass through two environmentally-challenged communities, Curtis Bay and Turner Station. They are considered historically underserved communities of color, disproportionately burdened by legacy pollution from nearby industrial facilities that are emblematic of environmental racism.

Located on the industrial south side of Baltimore, Curtis Bay is next to coal piers, petroleum storage facilities, landfill sites, a wastewater treatment plant and the largest medical waste incinerator in the U.S. Not far from Curtis Bay is Turner Station, an historically Black community surrounded by a landfill, a gas power plant and interstate highway, in addition to legacy pollution from now-idled industrial sites. Increasing rains and frequent flooding further expose both communities to the uneven impacts of climate change. 

In November, the EPA selected the Maryland Department of the Environment to receive almost $500,000 grant for additional but unrelated air pollution monitoring in four communities, which included Curtis Bay and Turner Station. 

Ren and Stratton set out for Baltimore around 10 a.m. with Stratton behind the wheel and Ren settled in the rear with the gear, with sensor readings on a laptop indicating concentrations of methane, carbon dioxide, carbon monoxide and black carbon in the ambient air, resembling a heartbeat on an EKG monitor. When the screen showed an uptick in methane levels, Ren checked whether the spike was above normal, and when it was, made a note of it. 

Stratton said they do mobile measurements two to three times a week and try to cover different weather conditions on different days and seasons, Stratton said, adding that they also used small aircraft to make similar measurements at higher altitude above the same area. Additional data came from stationary sources placed around Washington, D.C. and Baltimore for weather-related measurements that further helped refine the analysis.

Since the start of the project over a year ago, Ren and Stratton have clocked roughly 2,000 miles and 100 hours of mobile surveys since the spring. The project, run by NOAA’s Air Resources Laboratory, is expected to continue for another five to 10 years and will be extended to New York City and the Marcellus Shale area in Pennsylvania, with significant methane emissions from natural gas operations. 

Earlier in 2022, NOAA scientists reported a record annual increase in atmospheric methane for the second consecutive year. During 2021, the analysis estimated the annual increase in atmospheric methane at 17 parts per billion (ppb)—the largest annual increase since 1983, when the measurements began, and around 162 percent greater than pre-industrial levels. Meanwhile, carbon dioxide concentrations also continue to climb at historically high rates, NOAA reported. 

“Our data show that global emissions continue to move in the wrong direction at a rapid pace,” NOAA Administrator Rick Spinrad said at the time. ”We can no longer afford to delay urgent and effective action needed to address the cause of the problem—greenhouse gas pollution.” 

The mobile monitoring by Ren and Stratton, now on their way to Baltimore, keeps tabs on climate warming greenhouse gas emissions and potentially helps reverse the trend through the  sharing of emissions data with policymakers.     

Each fresh survey allows Ren and Stratton to assess if the emissions are consistent with previous observations, which is important for climate modeling based on their work. “We’ll be able to couple all of this information to look at the regional outflow of greenhouse gases and pollutants in the Washington, D.C.- Baltimore area,” Stratton said, his gaze fixed on the road.

“We also want to see any changes before and after the air pollution regulations are implemented. That way we can see how effective these measures are in curtailing global warming,” Ren said as they approached the Quarantine Road Sanitary Landfill, a composting facility on Baltimore’s industrial west side.

The methane tracker on Ren’s laptop jumped a few decimal points as the SUV drove around the site. “We’re just getting into the methane plume and we can see methane concentration increase from about 2.17 to about 2.6 parts per million, ” said Ren, adding it’s not a significant increase. Parts per million is commonly used to measure concentration of gases such as methane and carbon dioxide.  

He said that another way to tell if a methane leak is coming from natural gas infrastructure or a landfill site is to look for traces of ethane—a greenhouse gas and a key component of natural gas. “Methane is easier to control than carbon dioxide because it leaks from point sources,” Ren said, “which can be controlled by fixing broken gas pipes and by employing effective management practices at landfills.”

He said that their measurements show that landfills have gotten better at managing emissions. 

Next stop on the list were the coal piers, roughly a 10-minute drive from the landfill site, located in Curtis Bay next to several other landfills and an incinerator. A 2017 research by Environmental Integrity Project, a national nonprofit, showed the highest asthma hospitalization rates in Curtis Bay and neighboring areas next to a trash incinerator that emitted toxic air pollutants for decades.   

In December 2021, the neighborhood was rattled by the explosion at one of the silos at the coal terminals operated by CSX, shattering windows and endangering lives. Residents called the incident another in a string of environmental injustices, demanding that coal exports be suspended from south Baltimore. The company blamed the explosion on methane buildup inside the tunnel at the facility. The Maryland Department of the Environment has since fined the company for noncompliance. But residents say nothing much has changed. 

“Today the wind is blowing away from us. So, we only got into the plume for a short time and I don’t think we will be able to get to the center of the plume,” Ren said, watching the methane graph on the screen as they passed the coal piers. When the wind conditions are favorable,  methane enhancement is significant, which he said was typical of what they witnessed during previous sorties.

The results from the earlier mobile surveys from March to May detected elevated levels of methane, ethane and black carbon around Curtis Bay coal piers. But that was not the only source of methane in the area. The data showed that other pollution sources in the vicinity, such as oil and gas operations, diesel traffic and landfill sites, among others, sometimes emitted more methane than the coal pile. The results also showed that nitrogen oxides and black carbon were most likely to pose a health hazard for the Curtis Bay community. 

Suddenly, a potent smell of rotten eggs filled the air as the NOAA SUV approached Baltimore’s Patapsco Wastewater Treatment Plant, next to the coal piers and one of the largest such facilities in Maryland. That’s the smell of hydrogen sulfide gas coming from the wastewater, Ren said, a biological component produced by the degradation of waste materials. The methane levels peaked on the meter, which Ren said were consistent with the earlier measurements near the plant. 

The measurements Ren and Stratton gathered in May flagged Patapsco as the highest methane leaking facility in the Curtis Bay area. “This data will be shared with the community groups as well as the Maryland Department of the Environment because they have the authority to regulate these point sources through regulations and better operational practices,” Ren said. 

Early in 2022, Patapsco was discharging so much raw human sewage that state officials ordered remedial actions, requiring the city authorities to address long-standing systemic and operational problems that led to the excessive pollution flow into Chesapeake Bay tributaries.  

Four hours into their drive, Stratton and Ren turned back toward College Park through Turner Station and downtown Baltimore. Ren noticed methane leaks again and again while driving through the Turner Station area and in downtown Baltimore, occasionally taking notes in his log book that he said needed to be communicated to the city departments or gas companies to find and fix the leaks. 

“Everything kind of went to plan today. You never know exactly what you’re going to see when you’re doing one of these sampling missions,” Stratton said. “We planned the best we could and if the wind direction shifted on us a little bit, we were able to compensate accordingly and kind of sampled everything we set out to sample. I think today is going to be a very good dataset.”

Ren agreed, adding that what they saw again today was consistent with their earlier observations. “It’s important for us to check if these hotspots have changed over the last few months. I think all in all, it was a successful operation,” Ren said.

Back outside the NOAA building. Ren and Stratton downloaded the data before heading inside. 

The five-hour drive to Baltimore and back had yielded around 200-300 megabytes of data that Ren and Stratton will be analyzing the next day. Reviewing data from previous missions, they explained, is also critical to understand if they could have captured an emissions source better, which helps better plan future missions better. 

“I think,” said Ren, “our work will contribute to the reduction of greenhouse gases and slow down global warming.”