Excellent question. But current instrumental tools we have focus on volatility and water solubility as well as aerosol mass spectrometry. The latter requires notable amounts of mass especially if we have a cocktail of multiple compounds in single particles. There are some studies on UFP and AMS available, which resolve the upper size range of UFPs (~30-50nm) but battle with explaining 100% of the mass. Thus, same accurancy? No. Physical measurements are much easier than chemical ones.

I pressume the development of novel techniques is needed in here, e.g. exposing the measured particle size distribution to different sets of chemical compounds like NOx or OH and ozone. A second way might be to expose a sensitive target to those UFPs and detect chemical or optical changes compared to a non-treated reference over time.

A further aspect worth consideration is probably the travelling route of UFPs in human bodies, i.e. alveoli, blood, brain and organs and the chemical processing of different aerosol constituents at different sizes.

Good luck with your search!

You may try neutron activation analysis (NAA) to determine the trace element composition of UFP. This method is rather accurate with less problem on sample contamination. In a typical analyses, you can obtain about 15 elements depending on the detection limit. But, the limitation of NAA is that it is not sensitive for Cd and Pb.

However this method most probably will fail with the two problems UFP analysis displays, i.e. (1) the small amount of particle mass, highly sensitive to smallest contribution of larger particles and (2) the very reactive nature of the chemical compounds, resulting in no chance to wait for collection of sufficient material and resolving only the more stable or inert species. This is different to the task of high number concentration measurements when performing the physical measurement.

As stated earlier so far I see only indirect methods being applicable but I am keen learning new approaches resolving that challenge named Francesca Constabile.

Excellent question

There are many analytical techniques capable of determining the concentration of trace elements in biological materials such as atomic absorption spectrometry (AAS), inductively coupled plasma mass spectrometry (ICP-MS), particle induced X-ray emission (PIXE), photon activation analysis (PAA), charged particle induced activation analysis (CPAA), Neutron activation analysis (NAA) etc.

*** Instrumental Neutron Activation Analysis (INAA), is one of the most extensively used methods for food and environmental studies due to its high sensitivity, precision, versatility and multi-elemental character.

Hi Francesca,

My own experience is certainly more on the side of the physical characterization of ultrafine particles, but have you considered collecting the UFP in a nano-MOUDI (Micro-Orifice Uniform-Deposit Impactor)? The second generation nano-MOUDI provides uniform particle deposition on collection substrates thanks to an internal stepper-motor that is rotating the stages. I believe the smallest size fraction starts at 10 nm and there is a 30 L/min version to reduce sampling time. You would then need to extract the particles from the stages with ultra pure water and perform chemical analysis, e.g. by using ion chromatography. I'm anything but an expert but do remember reading publications by CSIC Barcelona and ICPF Prague. Good luck!

Thank you all very much for your valuable answers.

Let me stress one important issue posed in my question. There are techniques to measure UFP chemical composition, indeed, and you described these. However, I wonder how accurate these techniques are.

Also, please note that these are all onffline methods, unfortunately.

I think there are a couple of potential obstacles, one of which (obtaining sufficient mass for offline measurement) has already been mentioned. Another may be the potential impact of the method of size selection on the sampled aerosol. Inertial methods (impactors, virtual impactors, cyclones) typically require a significant ΔP from atmospheric pressure in order to reach the cutpoint size of interest (typically 100 nm, but there are arguments for other cutpoints). Ambient UFP is often composed chiefly of semi-volatile compounds, thus there could be significant sample loss and the UFP sample could become skewed towards less volatile compounds. This can be exacerbated at the high flow rates often encountered when attempting to increase sampled mass over a specific time interval. Size selection by electrical mobility or by diffusion can be done at near atmospheric pressures, but such approaches limit the availability of off-the-shelf equipment for UFP size selection. Screen-type parallel-flow diffusion batteries are not common, but there are commercial examples available and they would be simpler to operate over longer, and potentially unattended, sample periods than a DMA. If you are limited to using inertial separation, keep a close eye on the ΔP attained at the planned sample flow rate and particle size cutpoint, and consider using a larger cutpoint size (~200 nm) to reduce ΔP.

Experimental studies on animals have shown that after intratracheal instillation of ultrafine particles (UFPs) a substantial fraction of the dose could translocate into the systemic circulation,and when deposited in the nose UFPs may even translocate via the olfactory nerve deeper into the animal brain. Because a similar investigational approach is difficult to apply in humans, we postulated that the excretion of black carbon particles in urine can be considered as a biomarker reflecting in addition to inhalation exposure also the translocating nature of these particles from the circulation into the urine. This has been substantiated by the detection and quantification of black carbon particles in urine of 289 children living in the northern part of Belgium with relatively low annual ambient black carbon concentrations in the study area (range from 1.07 to 1.96 µg/m³). The proof of concept underlying this application rest on the following facts: 1/ This is the first time that the presence of environmental carbon in the urine of children is identified which shows the ubiquity of this environmental pollutant. 2/ We showed that urinary carbon load was positively correlated with real-life medium-term and chronic exposure to combustion-related black carbon air pollution. This finding is important as it reflects the passage of black carbon particles from the circulation into the urine, even at low ambient air concentrations. 3/ Spiked urine samples follow a linear dose-response relation within a large exposure range. This is a major step forward in view of biomonitoring the individual exposure and the utility of this biomarker for improving studies of health effects at low exposure concentrations. 4/ Black carbon is potentially one of the most toxic constituents of the UFP fraction.

Article Children’s Urinary Environmental Carbon Load: A Novel Marker...

The short answer is yes. The problem is what do we want to measure and if we will be able to have a panoramic picture of the entire composition of the particles. There are several articles showing that differences in composition are linked to different toxic effects on different cell types, linked in some cases to different cellular mechanisms. How this differences in composition have an impact in a human, that is something more difficult to answer when it comes to small variations in composition. Size and composition are related due to the sources of emission, but considering the role of inhaled particles on health, it is quite important to push forward methods to evaluate in real time the composition of particles and if possible some other characteristics like the oxidative potential of the particles.

Different UFP particles sizes have indeed been associated with different effects (e.g. on Blood Pressure in children) with the number of the smallest particles having the largest effect, whereas the mass based measures showed no effect.

Article Blood Pressure and Same-Day Exposure to Air Pollution at Sch...

@ Tim S Nawrot

Thanks for your comment. Our first results on biomonitoring during CARE strongly support your findings. Details are reported by Costabile et al. (2017 - Atmosphere , 8, 249 - doi:10.3390/atmos8120249). In short, we carried out simultaneous quantitation of five urinary monohydroxylated metabolites of four polycyclic aromatic hydrocarbons (PAHs) . Very preliminary results indicate that human exposure to PAHs in the CARE experiment is measurable in terms of urinary concentrations of 1 and 2-OHNAP and its level can be attributed to the environmental pollution conditions of the experiment site. Preliminary findings strongly suggest that human exposure to PAHs can be correlated to eBC mass concentrations measured at the experiment site.

@ Ernesto Alfaro-Moreno

Thanks for your comment. During the CARE experiment, we also determined the oxidative potential (OP) by the 2' 7'-dichlorofluorescein (DCFH) essay, with 2 hour time resolution . Details are reported by Costabile et al. (2017 - Atmosphere , 8, 249 - doi:10.3390/atmos8120249). Briefly, we observed that the OP may increase with decreasing particle size, but only for certain conditions—i.e., the morning rush hour case-study, during our experiment. The same does not apply to the night peak

case-study, which shows the highest values of the BC mass concentration with small particle size, but has the lowest OP value.

The aerosol occurring at the night peak hour correspond to the lowest values of the OP and to the highest eBC mass concentration.

Conversely, the aerosol occurring at the morning rush hour might have significantly larger values of the OP if associated with smaller particle size. Indeed, at the morning rush hour we observed a particle size-dependent OP: the OP tends to increase with decreasing aerosol median diameter

These first results are under investigation.

Dear Francesca, the information you are providing is quite interesting. I'll read carefully the article you are sharing. You may be interested in what we did on the field some time ago: Article Evaluation of the oxidative potential of urban PM and its re...

term accurate always needs a definition. I would rather assume the problem is more to get info about the surface composition of the particles.