The most dangerous to human health are small aerosols of diameter less than 1 micron. They can penetrate the alveoli. What is worse, they can penetrate into the bloodstream. If the chemical composition of aerosols are toxic substances such as mercury, the situation is even more dangerous to human health. Therefore, in my opinion, it would be advisable to establish standards for the ultrafine particles.

Europe wants this too.. They are trying to consider PM1. I think ultrafines is harder enough to control and measure and the worst are not just ultrafine, but fine particles as well (pm1)

We do measure particles below 1 micrometer and there is no doubt that there are dangerous substances there...

Peters et al. (2009) found health effects of UFP in a study looking at the effects of the German reunification on air quality but no clear effects for any other pollutants.

Although a vehicle emission standard for particle number (PN) emissions has been established in Europe, any attempt to establish an Air Quality Standard would be hampered by the fact that emission models for ultra-fine particles (UFP) and particle number counts (PNC) are still in their infancy (Nikolova et al., 2011). Even in tunnels it is hard to predict PNC. This will make it very hard to devise policy plans that guarantee a decrease in PNC towards any PNC AQLV that would be suggested.

In addition given the very local nature of UFP PNC concentrations it would be very hard to agree on measuring strategies (e.g. exact location of monitoring stations relative to road) and measuring protocols (e.g. the importance of determining the exact nanometer cut-off point).

Hello Luis, I believe we have met once. I think this is a very good question. EPA has been considering this for many years now. I am uncertain about the direction they will go. The strongest evidence for a health effect appears to come from the toxicology literature. However, EPA makes its decisions based on a wider range of evidence, including the epidemiological literature. We know that such epidemiological data is challenging to collect for ultrafines since their concentrations are much more variable in time and space than fine particulates (PM2.5). Such monitoring networks for ultrafines are simply not well established in the United States, which means that the epidemiological studies necessary to support an ultrafine PM standard are quite limited and would need to come from other parts of the world, particularly the UK or other countries in continental Europe. Another fact that is hard to dismiss is the recent review of the evidence of health effects of ultrafine particles from the Health Effects Institute. This came to a fairly weak conclusion and argued that more evidence on ultrafine particles is needed. It emphasized the need for epidemiological evidence, as I have highlighted here. You might consider reading through the HEI review if you have not already. This is available on their website at http://pubs.healtheffects.org/view.php?id=394. I hope this answer is helpful to you.

I agree with some of the comments before regarding the challenge of adding a UF standard. However, some of the problems are the same for many pollutants that are local and traffic influenced. I am thinking in NO2, PM10 (Coarse particles) and some VOC which are usually monitored at central sites. However, largest effects are seen when the spatial components is involved. This lead that maybe regulating many pollutants will include more than just central site, but estimation of local/personal exposures (for instance, there is extensive literature of in-traffic exposure). How to fit this in a management plan is a challenge that I think environmental scientist need to enter. Regarding the UF vs PM1 standard, I think the PUF has a more local impact so a PUF standard will need to tackle that problem in a better way; thus, with a PUF standard we will likely be more stringent in traffic emissions/exposures than with PM1. Regarding the health impacts, I think more effects (both acute and chronic) will be seen once better spatial models are developed, and likely the time-series effects are just the tip of the iceberg. However, current evidence seems small (as stated by the HEI) but is growing. Maybe is better to try to include PUF regulation as part of fine particle regulation (maybe targeted as co-benefits? or something).

Pablo

Luis,

Do you have any direct link to the news that EPA is considering a PUF standard?

Pablo

Luis,

the obvious path towards a cleaner and safer air we will led us to handle new standards concerning particles smaller and smaller...then in a near future the ultrafine particle concentration measurement will be likely introduced by the regulatory authorities.

I think this is a great opportunity for researchers working in this field!

My main concern is: how the ultrafine particle measurement can be addressed by the authorities? Measuring the particle concentration of very small particle cannot be reduced to a fixed sampling point technique (typical of PM standards). In fact, the particle concentration of sub-micrometric particles is strongly influenced by the distance from the emitting source. As example, the measure in a not directly exposed site in an urban area could provide misleading data (please see the attached papers).

Luca I agree with you. What I see from my measurements in the urbanized coastal zone is that local sources are very important for small particles. But not only particle concentration measurement should be once introduced by the regulatory authorities but also chemical composition. And may be it is even more important...

Anita,

It would be terrific having a whole characterization of a site in terms of both physical and chemical analysis. Anyway, I think it is not suitable from an economic and technical (measurement management) point of view measuring "on-line" all the details of airborne particles.

Anyway, an a-priori source apportionment of the particular site (e.g. urban areas, highway surrounding, etc) could help in evaluating the typical sources (vehicles, residential heating, biomass burning, marine aerosol,...) of that site. In this way, the measure of the particle concentration level (without particle distribution, or chemical analysis) can be related to the concentration of other pollutant (likely emitted by the same source).

EPA's most current assessment of UFP is included in the 2009 PM Integrated Science Assessment, which you can find here:

http://www.epa.gov/ncea/isa/

The most current NAAQS for PM, the 2012 PM NAAQS can be found here:

http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_index.html

The NAAQS does not currently include separate standards for Ultra-fine PM. Speaking as a scientist and not as an EPA official, I can say that UFP measurement, assessment and epidemiology are areas of considerable ongoing research world-wide.

Hello Joseph, I was looking for the most recent standards that have probably been established by EPA for UFPs. Thank you for the link it was quite helpful