In air quality warnings issued by the state Department of Environmental Protection (DEP) and Allegheny County Health Department (ACHD) over the past few days, you might have noticed both agencies predicted air quality would improve in the afternoons.
GASP is pointing this out because it could provide citizens with one small step toward minimizing their exposure to harmful air pollution.
We graphed ACHD’s monitor data for fine particulate matter (PM2.5) and hydrogen sulfide (H2S) concentrations since Nov. 3 and found that the agencies’ predictions were very accurate.
The takeaway? Spending time outside at 3 p.m. versus most of the late-night hours would likely result in lower exposure to those pollutants.
Of course, needing to schedule your day around air pollution in a first-world nation during a pandemic is appalling on many levels. And yes, regulations meant to control emissions during periods of stagnant air in our region absolutely are lacking and must be updated.
Unfortunately, relief from those issues won’t happen overnight. In the meantime, and if possible, spending time outside when pollution levels are lowest is one way to protect your health.
But of course, “if possible” invokes an entirely separate set of concerns: The reality is that many among us cannot schedule our time outdoors to avoid higher levels of pollution. Jobs, errands, children (human and fur kids alike) all might require time outdoors irrespective of the air quality at a given time.
When that is the case, it’s worth noting that the same masks that departments of health around the world are encouraging individuals to wear to slow the spread of COVID-19 might also provide some protection from high PM2.5.
As much as we wish we could, please understand we cannot say how much of an impact any of these steps would have. Indoor air can have its own sets of issues and masks can’t catch 100 percent of airborne pollutants.
In addition, the Environmental Protection Agency (EPA) does not have a one-hour concentration standard for fine particle pollution so there isn’t clear guidance on the harm of a few bad hours.
Currently, EPA requires that the annual average concentration for fine particulate matter is less than 12 ug/m3, averaged over three years and that no more than eight days per year, averaged over three years, have a concentration exceeding 35 ug/m3.
Over the past few days, daily concentrations at monitors in Liberty and Avalon exceeded EPA’s daily standard and several hourly concentrations were more than double the limit. That said, the lack of an hourly standard and the eight-days-per-year clause in the daily standard mean these “exceedances” of the limit might still comply with the EPA rules.
Our point? That within the 24 hours composing those daily exceedances, some hours were much better than others. Taking steps to avoid the worst hours could provide some relief if you’ve been affected or are concerned about the potential health impacts.
Finally, we’d like to note that this pattern of pollutant levels increasing overnight and decreasing during the day is somewhat common for fine particulate matter and hydrogen sulfide but NOT ozone. In fact, when ground-level ozone levels get close to exceeding health-based air quality standards, the highest concentrations will be late in the afternoon.
We are entering a period of the year when ozone isn’t a problem but it’s worth pointing out the pattern of pollution we’ve seen the past few days isn’t a universal rule for all pollutants.