Uncertainty in the quantification of odour measurements is a difficult (but needed) task. Critical aspects include panel selection (required by dynamic olfactometry), sampling, and stability of the samples. Proficiency tests (PTs) can help evaluate such contributions; however, the classical approach to PTs, in which laboratories analyse real samples taken from the field, are not as applicable in this field, and are often implemented by only using dry gas cylinders containing stable compounds. Consequently, uncertainties related to the sampling activity cannot be assessed. In particular, high odour levels and the presence of water vapour in emission sources can create significative biases due to sampling techniques used and chemical reactions that can occur before analysis. In this work, we present experimental notes, developed using the experimental facility ‘LOOP’, realised at the RSE research centre in Italy, in order to “help” the definition, in an upgraded protocol for implementing PTs for odour determinations. Using this bench loop is advantageous as it involves the possibility of implementing samples in conditions very similar to reality (i.e., high temperatures, high water content, and the presence of chemical interferents).

Formaldehyde (H−CHO) is a chemical compound extremely common in many industrial productions. However, in 2004, it was reclassified as carcinogenic (H350) and mutagenic (H341). Therefore, stringent limitations on emissions were implemented; among them, the lowest limit (3 mg/m3) was adopted by some Italian Local Competent Authorities. Up to now, no European-validated method for emission control was available, and for this reason, a specific working group (WG 40) has been created in the framework of the European Committee for Standardization Technical Committees 264 (CEN TC 264) to publish a qualified method for the quantification of Formaldehyde emissions from stationary sources (i.e., power stations, incinerators, petrochemicals, and industrial plants that uses combustion for their energetic purposes). Some preliminary trial tests were conducted to evaluate (1) the sampling protocol, and (2) the analytical technique. From a measurement perspective, two methods were selected: EPA 323—VDI 3862-6 and VDI 3862-2. Every new method prepared by CEN shall be verified before publication in the field and in real conditions to verify its metrological properties (i.e., precision, biases, reproducibility, and repeatability), costs and the training needs for involved personnel. With this aim, two measuring campaigns were conducted, and some important conclusions emerged concerning the H−CHO sampling procedure. Due to high water levels normally present, condensation during sampling is critical and can cause unpredictable errors; wet traps (impingers) give good responses. The sampling in pure water appeared unstable, but using an H2SO4 solution solved this issue, thus being recommended.

The role of the elemental carbon (EC), in synergy with hygroscopic ionic species, was investigated to study the formation of electrical bridging phenomena once the aerosol deliquescence is achieved. Ambient aerosol samples were collected on hydrophobic surfaces in urban and rural sites in Northern Italy; their conductance was measured in an Aerosol Exposure Chamber (AEC) while varying the relative humidity. An electric signal was detected on 64% of the collected samples with conductance values (11.20 ± 7.43 μS) above the failure threshold (1 μS) of printed circuit boards. The ionic content was higher for non-electrically conductive samples (43.7 ± 5.6%) than for electrically conductive ones (37.1 ± 5.6%). Conversely, EC was two times higher for electrically conductive samples (26.4 ± 4.1 μg cm−2; 8.4 ± 1.7%) than for non-electrical ones (12.0 ± 4.1 μg cm−2; 5.2 ± 1.9%) suggesting that the synergy between the ionic and carbonaceous fractions is necessary to promote a bridging phenomenon. Synthetic aerosols (EC only, saline only, mixed saline and EC) were generated in laboratory and their conductance was measured in the AEC to verify the ambient results. Only in case of a contemporary presence of both EC and ionic components the bridging phenomenon occurred in keeping with the theoretical deliquescence values of each salt (R2 = 0.996).