Air Quality in NYC Subways: Worse Than You Might Think
Anyone who rides the NYC subway knows how unpleasant this environment can be. Whether it’s the noxious odors, the bustling crowds, or the ear-splitting noise, we all have our personal tales of subway horror. One day, a few weeks ago, I was waiting for the N train at Times Square. After a few moments, the train rumbled in, bringing with it a powerful blast of stale, dusty air. Bracing myself against the sudden onslaught of grime-laden air, I pondered what unseen pollutants could be lingering around me. Lead dust? Mold? Bacteria? Surely the city must keep track of this, I thought. Out of curiosity I went to Google and searched: Air Quality in the NYC Subways. Scrolling through the results, I found surprisingly little research on the topic of air quality in the subways, save for one study from 2005 on airborne metal dust. I came across a few studies conducted in the Toronto and Barcelona subway systems, but next to nothing is known about conditions in our transit network. I found a great deal of information about outdoor air quality in NYC, which comes as no surprise. The city operates an extensive above-ground air quality monitoring network. Its data is publicly available. But, as for the information on air quality for the subways (they do collect this information), it isn’t made public.
The dearth of research both shocked and motivated me. Here was a great opportunity to use my knowledge and skills to investigate an issue that affects millions of New Yorkers everyday. As an environmental specialist, I spend a lot of time working with clients on air quality-related issues. At the company I work for, Green Orchard Group, we use a variety of tools to accurately evaluate indoor air quality for clients. Utilizing some of those same tools, I set out to answer my question — What’s in the air we breathe? — by conducting an informal air quality assessment in select subway stations.
I considered what data to collect for the study. The first parameter that came to mind was particulate matter, more commonly known as simply “dust.” To many readers, airborne dust may not seem like a big deal, but in recent years, scientists have been sounding the alarm about the hazards posed by particulate matter, especially fine particulates. Fine particles, referred to by scientists as PM 2.5, are microscopic particles in the air which, when inhaled, can penetrate deep into the lungs and even pass into the bloodstream. Technically speaking, PM 2.5 is the weight in micrograms of particles measuring less than 2.5 nanometers per cubic meter of air (μg/m3). Elevated PM 2.5 concentrations have been correlated to an increase in the risk for developing a variety of conditions from asthma to heart disease and even depression. Quantifying the levels of fine particles in the subway environment represents an important data set since 6 million people, including myself, spend a significant portion of their day traversing the system.
Thanks to recent advances in sensor technology, collecting real-time, accurate data on particulate matter is fairly easy and straightforward; all I have to do is use a portable sensor. For this, I utilized a Temtop LKC-1000S+, an affordable, simple tool that uses a built-in laser to measure ambient particles. With this device in hand, I set out to measure the PM in a select group of subway stations and trains. My methodology for collecting data consisted of recording PM 2.5 concentrations in the locations for a total of 5 minutes per location. From these readings, I calculated the average PM 2.5 level for that site. Data was collected on the afternoon of December 18th, 2019. Outdoor air quality in NYC was considered “good” that day according to the NY Department of Environmental Conservation’s air quality website.
Before we get into the results it’s important to define what constitutes a “good” or “unhealthy” level of particulate matter. For that we use standards published by the EPA. Keep in mind these standards are based on 24-hour exposures. In other words, exposure time is a crucial factor when determining the risk posed by poor air quality.
Results
Let’s start with the good news: Testing inside the subway cars revealed low levels of particulate matter. Since the subway cars are equipped with HVAC systems, this result comes as no surprise. However, concerning levels of PM pollution were found in all but one of the eight subway stations sampled. Grand
Central and Boro Hall stations exhibited unhealthy levels of air pollution. Several readings at Boro Hall exceeded 120 μg/m3, which is nearly three times the average concentration measured in Beijing, one of the world’s most polluted cities. The air quality at both Atlantic Terminal and Herald Square ranked as “unhealthy for sensitive groups.” The Lorimer Street station on the L line had the cleanest air — all readings were below 12 μg/m3. Generally, PM 2.5 concentrations tended to spike with the arrival or departure of trains, which presumably arises from the mechanical action of the train disturbing dust on the subway track and platform.
This simple study confirmed what I and probably most of my fellow commuters assumed: that the air quality in the subways is less than satisfactory. However, it’s important to point out that the data reported here present only a “snapshot” of the conditions in select stations at a particular moment in time, and can’t be construed to indicate these contaminant levels persists through time, or are representative of the system as a whole. I don’t purport to portray this as a rigorous scientific study, it’s not. That said, these results highlight a hugely understudied public health risk, which is really the primary take-away message — that the city should be doing more to study and ultimately mitigate the problem of poor air quality in our subway system.
Follow up
I collected several air samples and sent them to an accredited environmental lab for analysis. Those results are pending…
