Assessing Outdoor Air Near Schools
Resampling for Volatile Organic Compounds (VOCs) at Selected Schools - Questions and Answers
EPA is extending monitoring at a number of schools across the country for a group of pollutants known as volatile organic compounds (VOCs). A malfunction in monitoring equipment at those schools caused some VOC samples to become contaminated. EPA and its state and local partners will take additional samples to ensure that the monitors provide an accurate picture of VOC levels in the outdoor air. The questions and answers below describe the malfunction and the steps EPA is taking to get additional air quality samples for VOCs.
- Why are you re-monitoring at some schools?
- How many schools will resample for VOCs?
- When will resampling begin?
- How did the VOC samples become contaminated?
- How did you determine which schools would re-monitor?
- Were all of the samples at these schools contaminated?
- What pollutants were found in the VOC samples as a result of the contamination?
- Could you miss something dangerous in the air as a result of invalidating contaminated air samples?
- Could the leaky timer box have caused some results to indicate lower levels of pollution than actually are in the air?
- How did you find out the timers were leaking?
- How can you tell the difference between a contaminated air sample and an air sample that is measuring real pollution around the air outside a school?
- Are you resampling for all the pollutants, or just VOCs?
- Why aren’t you measuring other pollutants at the same time?
- It looks like you are going to repeat some of the samples at my school. Why not all 10 samples?
- The numbers that you posted for my school have changed. Why?
Q: Why are you re-monitoring at some schools?
A: We want to be confident that the air quality samples from the schools give us an accurate picture of what’s in the outdoor air at those schools. But at a number of schools, a timer malfunctioned on monitors designed to measure a group of pollutants known as volatile organic compounds, or VOCs. The timer malfunction – a leak in the timer box - caused some samples of air to become contaminated, so they don’t show us actual levels of pollution in the outdoor air.
Q: How many schools will resample for VOCs?
A: Twenty-four: 23 schools will extend VOC sampling because they have had data invalidated as a result of the timer leak; sampling will be extended at one school where samples were valid (Felton Elementary School in Lennox, Calif.) at the request of the local air quality agency; EPA is evaluating results from one school (Olean Middle School in Olean, N.Y.), to determine whether resampling is necessary.
Q: When will resampling begin?
A: It varies by school. Some state and local agencies already have begun taking the new samples at their schools; others will wait because of issues such as weather or scheduled construction. We anticipate most schools will have completed resampling by March 2010.
Q: How did the VOC samples become contaminated?
A: A leak in a fiberglass box housing a timer for the monitor allowed air from inside the box – not just air from the outside -- to get into the canister containing the air quality sample. The air inside the box contained some chemicals, which were emitted by the box and its contents. When the timer box leaked, those chemicals contaminated the samples. As a result, when the samples were analyzed, it appeared that there were pollutants in the air around some schools that 1) may not be there at all, or 2) may actually be in the air, but at smaller concentrations.
Q: How did you determine which schools would re-monitor?
A: We invalidated samples at any school where the VOC data indicated that the timer box had leaked. We see a distinct pattern in the chemicals measured by the monitors with the leaking timer devices. The results of these samples show certain chemical compounds – primarily acrylonitrile and dichloromethane – at levels that are not typically seen in the outdoor air.
If the data showed signs that the timer was leaking, we invalidated samples collected with that monitor -- from the beginning of the monitoring until the timer was either 1) removed; or 2) sent to EPA’s lab to have a stabilizer installed that prevents the leak from occurring.
Those schools – there are 24 – will collect additional VOC samples to replace those that were invalidated. EPA has determined that samples from an additional 17 schools monitoring VOCs were likely not contaminated; however, monitoring will be extended at one of those schools at the request of the local air agency.
Q: Were all of the samples at these schools contaminated?
A: No. From the sample results, it appears that the timers may have leaked on some days and not others. But we have decided to take a cautious approach. Because of this, we will invalidate any samples that were taken with a VOC monitor with a leaky timer – even if it appears not to have leaked on the day a particular sample was taken. We are working with our state and local partners to conduct additional VOC monitoring to replace the invalidated samples.
Q: What pollutants were found in the VOC samples as a result of the contamination?
A: The majority of the contamination comes from two VOCs: acrylonitrile; and dichloromethane (methylene chloride). We also have seen smaller amounts of acetonitrile, acetylene, ethylbenzene, xylene, toluene and styrene. In some cases we are also seeing very small amounts of acrolein.
Additional information on acrolein. While we have found acrolein in some VOC samples that we know to be contaminated, we also have other monitoring data showing elevated levels of acrolein in many areas of the country. This information was from samples that were not contaminated. We are conducting additional, unrelated laboratory testing to further check whether monitoring results for acrolein are affected by the type of canister used to collect the sample and how that canister is cleaned.
Q: Could you miss something dangerous in the air as a result of invalidating contaminated air samples?
A: We are invalidating air samples that are not accurate, and will resample to ensure that the air samples are accurate. If there are pollutants in the air around the schools, we will see that in the new results. We will monitor until we get a sufficient number of valid samples at each school to allow us to project long-term concentrations of air toxics.
Q: Could the leaky timer box have caused some results to indicate lower levels of pollution than actually are in the air?
A: No. The leak occurred where the timer box attaches to the canister that collects the sample of air – not in the canister itself. That allowed air from inside the box, which contained some of the pollutants we are trying to measure, to get into the canister. It didn’t allow air to get out. The contaminated samples would show higher levels of pollution, not lower ones.
Q: How did you find out the timers were leaking?
A: Relatively elevated values of acrylonitrile and dichloromethane were first noted at two of the school air toxics monitoring sites in Los Angeles. The South Coast Air Quality Management District then placed its own VOC monitors at these sites for comparison. Their monitors showed levels of pollutants that were more in line with what they had typically seen in that area.
In addition, EPA had previously placed two monitors at some schools as a quality assurance check. The monitors should have shown similar results. But at several schools, the VOC readings varied, further indicating that we had a problem.
To help us find out what the problem was, EPA’s lab sent a replacement monitor and timer to one of the Los Angeles area schools. When the lab received the original monitor, technicians noted that two fittings on the timer box were loose. That’s when the leak was first suspected.
To confirm this, the lab used the returned monitor (with the loose fittings on the timer box) to analyze a sample of clean air. The lab found elevated levels of dichloromethane, acrylonitrile, toluene and styrene. Because the lab knew that the air it had collected was clean, it could determine that the pollutants came from inside the timer box and contents.
The laboratory then repeated this test several times, all with similar results.
Q: How can you tell the difference between a contaminated air sample and an air sample that is measuring real pollution around the air outside a school?
A: We see a distinct pattern in the chemicals measured by the monitors with the leaking timer devices. The results of these samples show certain chemical compounds – primarily acrylonitrile and dichloromethane – at levels that are not typically seen in the outdoor air.
Q: Are you resampling for all the pollutants, or just VOCs?
A: At most schools, we are only resampling for VOCs because we have determined that we already have a sufficient number of valid samples for the other key pollutants. In addition to those air quality samples, we will examine data on wind direction and speed from meteorological stations located at the schools, along with data on historical wind and weather patterns in the area. This will help us understand whether the snapshot of pollution levels we have taken represents long-term conditions at the schools.
While the results for acrylonitrile and dichloromethane are most affected by the leak, we will resample for all VOCs being monitored at the schools. This includes acrolein, benzene and 1,3 butadiene, which are the VOCs of key interest for this effort.
We are conducting additional, unrelated laboratory testing to further check whether monitoring results for acrolein are affected by the type of canister used to collect the sample and how that canister is cleaned.
Q: Why aren’t you measuring other pollutants at the same time?
A: While that would be ideal, at most of the schools being monitored, we already have a sufficient number of samples of the other key pollutants we are monitoring. In addition to those air quality samples, we will examine data on wind direction and speed from meteorological stations located at the schools, along with data on historical wind and weather patterns in the area. This will help us understand whether then snapshot of pollution levels we have taken represent long-term conditions at the schools.
Once the VOC monitoring is complete, and we have analyzed VOC results along with results for other pollutants, we will be able to determine whether any additional monitoring is necessary for us to understand whether levels of air toxics pose health concerns at a particular school.
Q: It looks like you are going to repeat some of the samples at my school. Why not all 10 samples?
A: We don’t want to repeat monitoring where it isn’t necessary. So if data indicate the VOC timer was leaking at a school, we are invalidating samples from the beginning of the monitoring until the timer was either 1) removed; or 2) sent to EPA’s lab to have a stabilizer installed that prevents the leak from occurring. At some schools, this means we’ll repeat all the samples; at others, we’ll only have to repeat a few.
Q: The numbers that you posted for my school have changed. Why?
A: Because of the timer leak and sample contamination issue, we are invalidating a number of samples and will resample at a number of schools. But in a few cases, we had collocated monitors at the schools – meaning we put out two monitors to measure the same pollutant in the same location. Installing two monitors at some sampling locations is a common quality assurance practice.
At schools where we had an EPA or approved state collocated monitor, we are allowing states to substitute data from the secondary monitor, provided the samples do not appear to have been contaminated. If the numbers for your school changed, it is because this type of substitution took place.