I can think of two areas:

1. Continuing to reduce the cost and complexity of respirable a aerosol monitoring to allow increased monitoring sites.

2. Development of ultrafine particulate matter reference methods to support epidemiological studies of UFP in occupational exposure settings.

I think the next chalenges would be to study exposure to nanoparticles in daily activities and epidemiological studies related.

Improve studies in cause-efect exposure impact

Thanks for the reply.

I agree nanoparticles/ultrafine particles are an important topic of research in aerosol monitoring. How cheap should be a monitor for ultrafine particles for investingating daily activities? Which metric should be used?

Because of it's size, UFP often is not a major contributor to PM mass via gravimetric measurement. UFP has a fairly large response for metrics such as particle number or particle surface.area, so those may better metrics for UFP. There are challenges with respect to the sampling protocol. In many cases, occupational and ambient UFP are dominated by semi-volatile aerosols, so the operational temperatures and pressures of the sampling system are important. Because of the Brownian motion of UFP, diffussional losses also have to be carefully considered within the sampling train design. For research metrics, the mini-DISC diffusional classifier (Fierz et al. 2011, http://dx.doi.org/10.1080/02786826.2010.516283) would allow measurement of particle number via integrated particle size and the size-distribution information could be used to infer particle surface area. Miniaturized condensation particle counters (He et al. 2013, http://dx.doi.org/10.1080/15459624.2013.766555) with inertial size-selective inlets or coupled with a diffusional classifier might form the basis of a UFP montitor for daily activity.

http://dx.doi.org/10.1080/02786826.2010.516283

Link to He et al.2013 paper:

http://dx.doi.org/10.1080/15459624.2013.766555

I have held for a long time that the development of exposure modeling of aerosols would bare the most fruit. We have done source experimental characterization of aerosol sources and there is no reason it would not work with nano-particulate as well.