Kathleen Z. Rooney
Particle pollution, PM 2.5, is harmful to human health. PM is usually categorized as coarse (PM10 > 10 ug) and Fine (PM 2.5 < 2.5 ug), with the fine being most risky to human health. Fine particles can penetrate more deeply into the lungs. In particular, students on school buses are at highest risk, with their prolonged exposure to the bus cabin, faster respiration rates and smaller airway passages, into which ultra-fine particles may be respired. Current EPA regulation restricts PM 2.5 levels to 15 micrograms per cubic meter of air
(
Μg
/
m
3
) as an annual average. New Haven achieved an annual average of about 10
Μg
/
m
3
, in 2009 but within the annual average were some very elevated days. Here we can contrast an annual value of 5.36
Μg
/
m
3
in Litchfield, nearly half the value of New Haven.
4
So, what are the risks with particulates? Recent prospective studies have shown a modest increase in risk of developing asthma, associated with elevated levels of PM 2.5.
5
It is very possible that the increased levels of asthma in New Haven are in some part due to the higher levels of PM and other air pollutants. Children in New Haven have a 15% chance of having asthma, contrasted with about an 8-9% chance nationwide.
6
The 2002 study entitled, The
Concentration-Response Relation between PM 2.5 and Daily Deaths
focused on correlating daily death rates and ambient levels of PM
2.5
" found an essentially linear relationship down to 2
Μg
/
m
3
" There appears to be no lower threshold in the effect of particulates. Their conclusion," The magnitude of the association suggests that controlling fine particle pollution would result in thousands fewer early deaths per year.
7
In January, New Haven recorded daily averages of 36, 43 and 55
Μg
/
m
3
PM
2.5
8.
However, when these peak days are averaged in with the rest of 2011, it is possible that New Haven may achieve overall annual compliance for the year. Yet the EPA recognizes that temporary peaks do present a risk. The federal EPA guideline limits PM 2.5 to 35
Μg
/
m
3
within a 24 hour mean, making the three dates in January out of compliance.
In a brochure simply entitled, Air Pollution" The EPA says this of short term exposures to particulate matter:
"Short-term exposures can aggravate heart or lung diseases leading to symptoms, increased medication use, hospital admissions, ED visits, and premature mortality; long-term exposures can lead to the development of heart or lung disease and premature mortality."
Some studies have focused on the short-term exposures and associated risks, and it is these to which our work will pay particular attention. The problem our class will quantify is what are the health impacts on children's asthma symptoms, when exposed to higher levels of particulates.
Many observations of the effects of PM 2.5, have tried to quantify the air concentrations that harm human health. A study of children in Seattle, released in 2005 showed associations between short-term increases in PM 2.5 levels and the increase in asthma symptoms. The researchers examined hourly and daily cumulative averages, rather than annual levels of PM 2.5. The study aligned the peaks of particle concentrations with peak symptoms. Their work noted delays is reactions of 1 to 12 hours, with statistically significant associations between short-term increases in particle pollution and airway inflammation. The study notes specific and measureable responses in airway inflammation in rises of as little as 10
Μg
/
m
3 9
.
A later (2008) study in Mexico City looked at several markers of lung distress. The lung inflammation was associated with a 17.5
Μg
/
m
3
rise in PM 2.5 and measures of lung force were significantly lowered after 4-5 days of cumulative exposure. This effect occurred in asthmatic and non-asthmatic subjects. "The effect appears on the same day as the exposure and can cumulate over several days, resulting in lung function decrement after 4 or 5 days of cumulative exposure.
10
" These previous works were corroborated in a 2010 study linked with the Children's Health Study in southern California. With a sample of 2440 children, this much larger study showed a 17% rise in the level of inflammation markers to be significantly associated with a modest 7.5
Μg
/
m
3
rise in PM 2.5.
11
Based on these studies, we can see that normal concentrations of PM 2.5 in New Haven are already presenting a measureable threat to health, as they clearly exceed the 7.5
Μg
/
m
3
level and often reach the highest estimate of 17.5
Μg
/
m
3
. In addition, students who embark on a bus ride will face an additional exposure, or dose that will cause an additional level of response. The 2002 study that correlated PM 2.5 levels and daily deaths argues that no elevation in particulates is safe, our question is: when is the risk too great?
