Increasing ultrafine particles, engineered nanoparticles, non-regulated air pollutants are emerging pollutants which can cause even more danger to health than classical air pollutants. In that context, is air quality really getting better ?
Yes, speaking for the US, as a whole air quality is getting better, although progress on ozone has slowed greatly. In some areas, ultrafine particles were observed to decrease since 2000 and increased slightly as the 2008-10 recession lifted, increasing VMT. Many air toxics like benzene have also decreased. What data we have on the largest health effects of air pollution are related to the classic pollutants - fine particles and ozone (not to mention lead in the past); the unmeasured pollutants would have to have very strong effects and be increasing a lot to counter the benefits we have already measured from fine particle and ozone reductions. To date, the extent of transport and exposure e.g. ultrafine partilcles as compared to fine particles would seem to make such a scenario unlikely. None of is to say that we should not continue to study and work to reduce both regulated and non regulated pollutants.
But this is mainly about the US both in urban areas and regions. Globally, exposures to the 'classic' indoor and outdoor air pollutants remain a major contributor to morbidity and premature mortality, with on the order of 7 million deaths per year. And background ozone transport is likely getting worse, driven by increasing in methane emissions. Reducing methane is also critical for addressing global warming, but the US is working to pull back on current regulations.
John
Thanks for your answer
How do you know that ultrafine particles (UFPs) are diminishing. ? PM2.5 and PM10 diminishing does not mean UFPs also diminishing. Also the mass may diminish but the number of nanoparticles increasing. I believe that the number of UFPs is more important than the mass. Now what about NH3 ? I think it is increasing too. Background ozone as well. My point is that classical pollutants are decreasing of course in US and Canada but what about emerging pollutants, nanoparticles, butadiene, carcinogenic VOCs, transition metals, etc. ? They are more and more cancers, respiratory diseases, etc. There are more and more sources of emissions also but it hard to believe that we really breathe better air. The micropollutants are invisible and difficult to measure and have less obvious immediate impact on the body. To me it is like saying, well there is no more bank robbery so we need less police. But there are new kind of crimes: fraud on internet, stealing identities, etc. I think although there were progress in improving air quality in Us and Canada, emerging pollutants are threatening us and we should start monitoring those. Financial restrictions should not be an excuse.
There's been a long-term study in Rochester NYArticle Long-term trends in submicron particle concentrations in a m...
that shows UFP fell along with other pollutants through 2008, with some increases thereafter. One site is obviously limited, but the indication is the small increase was related to a local increase in VMT as the recession eased. VMT increased in much of the US over the same period, suggesting a possible small increase with VMT, yet the larger decreases that preceeded (before the recession) it are certainly tied to air pollution reductions, including reduced S in fuel and other measures in the heavily populated NE, in which Rochester is located. Bottom line, I don't know whether UFP are decreasing in every US city, and there may be more data I don't know about. But the Rochester example suggests a reason to expect a decrease in other US cities.
Alain, I realize I didn't address your other comments in my hurry to respond to the main question, but I am in general agreement with the thrust of your statement that we should worry about emerging challenges and provide better data for assessing the issues. One minor quibble - I'm not sure number is more important than size in terms of total effects, as UFP, even if they turn out to be more potent than fine particles, just can't end up exposing as many people as accumulation mode particles, which have that name for their persistence, long-range transport, and penetration indoors. This in no way means we shouldn't worry about people driving and living near roadways, who will have high exposures to UFP.
Yes PM2.5 and PM10 have diminished in North America but what about UFPs ?
Since the particle number concentration is rarely measured it is hard to say. And what about future ?. Any substances which are not regulated can grow without control and UFPs could be one of them. Samething with NH3 (which is not regulated in North America as well): it is growing substantially. Other substances such as butadiene (likely carcinogenic for humans and animals) is part of VOCs which is ignored, it seems. Also the engineered-nanoparticles (eNPs) are growing as well and rarely the impact on health have been studied.
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