Behind the Scenes at the Subway-Surface Air Flow Exchange (S-SAFE) Project

Before dawn on three days in July, some 20 Brookhaven National Lab employees, guest scientists, and collaborators, along with 100 student interns, gathered at several designated pickup locations in the New York City metro area to begin the process of deploying 200 air samplers and seven perfluorocarbon tracer release units as part of the joint Brookhaven Lab/New York City Police Department (NYPD) Subway-Surface Air Flow Exchange (S-SAFE) project. 

Scenes from the S-SAFE project

At a Long Island University (LIU) dormitory in Brooklyn, the samplers were carried down from their storage space on the sixth floor and stacked outside the building to await transport. Below-ground samplers were delivered by subway, while above-ground samplers were loaded onto NYPD vans to be driven to various locations throughout the five boroughs.  Student teams met the police vans, then secured the samplers in place and monitored them until 2 p.m. when the study period ended. The samplers were then returned to LIU, where the sample tubes were removed for transport to Brookhaven National Lab and the sampler units reloaded and prepared for the next study day. By the time the work concluded, most participants had put in a 12-hour day.

Working conditions were challenging. The first two days were hot, as expected, although the second day was brutal even for New York in the summer, with temperatures in the high 90s and the air heavy with humidity. On the third day, team members who prepared for heat wished they had not worn shorts as temperatures dropped, the wind blew steadily, and light rain fell sporadically.  But weather may have been the least of the challenges of this field study, particularly massive when compared to its predecessor, the 2005 Urban Dispersion Program (UDP).

“In terms of the operation and the coordination with the students and the NYPD, it was just an amazing field campaign – very large and complex and with very tight time windows.”

— Terry Sullivan, EE

John Heiser, group leader for Technology Development and Applications in the Environmental Sciences Department (EE), worked on both field studies, this time as co-project lead. He pointed out that while UDP had 64 samplers on the ground and a couple on building tops and in the subway, S-SAFE had 120 on the surface and 83 in the subways on each of the three study days. And while UDP’s two study days covered a limited area around Madison Square Garden and near the Time-Life Building in Midtown Manhattan, the area studied in S-SAFE stretched from Battery Park downtown to 161st  St. in the Bronx and also included areas of Brooklyn, Queens and Staten Island. 

“It was much harder getting everything out there, which is why we started at 4 a.m.,” Heiser said. “The subway teams had to travel so far that they needed at least a half hour to get to their spots before the samplers arrived.”

Heiser had high praise for everyone who worked on the project, particularly the students.

“It proved to me once again that student interns are a big help,” he said. “They performed quite well, better than the professionals in general. They had a lower error rate, maybe because they were more concerned about making mistakes.”

While UDP’s eight teams could easily monitor their samplers on foot, S-SAFE’s 25 teams relied on new technology to wirelessly monitor sampler performance. Andrew McMahon, an electrical engineer in EE, designed the electronics in the new samplers.

“We tried to come up with a system that could be used in the broadest range of future scenarios,” he said. “One of the major issues was developing a low-power system so it could run on batteries for a long period of time. We also decided to add some additional features like WiFi so it would be easier to communicate with them, program them and determine whether or not they are working in the field. We also wanted the ability to regulate the airflow through them in a controlled manner.”

EE’s Tom Watson, who also had a lead role in the UDP project, was very pleased with the new samplers.

“They were much more reliable,” he said. “It was much easier to keep track of how they were working because they were newer and had many more capabilities, so communication and programming were greatly improved.”

EE’s Scott Smith was responsible for planning the delivery routes as well as programming and deploying the seven release units.

“Logistically, it was the hardest experiment I’ve ever been involved with,” he said. “It was a great weight off my shoulders to have all those release units go on and off and dispense what they were supposed to dispense each time. And of 600 samplers — 200 on each of the three days – we had maybe 12 fail. That’s like two percent. If you’re doing better than 90 percent, it’s a home run.” 

The most notable sampler problem arose on the third study day, when a student checking on one of her samplers found it had disappeared, along with the light pole to which it was attached. The mystery was solved a few hours later: a truck had collided with the light pole and the city workers who responded to clean up the mess removed the sampler along with the other debris. It was recovered several hours later, with no damage to any of the sample tubes.

Rick Wilke’s responsibility during the field test was preparing all the sampling materials, which over the course of the study amounted to between 7,500 and 8,000 sampling cartridges that had to be cleaned, their barcodes scanned, and assignments made to a sampling device. At the conclusion of each study day, the samplers had to be checked in, their data sheets assessed, and the sample tubes removed and boxed up for transport back to the Lab. Wilke was also the leader of a subway team whose 14 sampling stations stretched from Brooklyn to Queens, and he spent much of the study period underground with no cell phone reception. 

“Every once in a while I would pop up to the surface and check my text messages to find out if there was a problem I had to address,” he said. “But my team essentially spent six to eight hours in the subway, which is not the most thrilling thing to do, although you can do a lot of people watching.” 

Wilke was also very pleased with how the study unfolded.

“The first day was a little bit crazy because people were getting accustomed to what their jobs were, particularly the students. Most of us have been doing field programs for 30 years, so while certain details may be different, we knew what to do. The interns we had were young and hadn’t been involved in something like this, and I was definitely concerned about their reliability.  But after the first day, they all knew what their jobs were and they really wanted to get it done correctly. That was a pleasant surprise – after three days, we were a well-oiled machine!”

Now that the data has been collected, the next phase of the project has begun. Wilke’s role now is analysis of the approximately 8,000 samples, which he hopes to complete within the next three months.

Terry Sullivan, who was a leader of a team of five students for an aboveground, 10-sampler route on study days, also has a major role in the post-field study analysis.

“How did it go? I think it was fantastic,” he said. “We’ll have to wait and see what the data tells us, but in terms of the operation and the coordination with the students and the NYPD, it was just an amazing field campaign – very large and complex and with very tight time windows. And it was fun!”  

Sullivan’s main role in the project now is to develop the decision-support software that will be the product delivered to NYPD by March 1. He pointed out that student interns are also involved in this phase of the project.

“We have a very rough prototype that some summer students have developed,” he said.  “It allows you to pick any release location and then calculate where the PFT goes throughout the whole subway system, based on the data we have. If you have an above-ground release, you can determine how it gets in the subway, where it moves, and when and where it emerges above-ground.”

While the students were a great benefit to the project, Heiser hopes some may also see new roles and career options for themselves as a result of the experience.

“They performed quite admirably, and some of them surprised me,” he said.  ”Some who I thought might be a little goofy or the class clown actually turned out to be true leaders. Maybe they also proved to themselves what they were capable of.”

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