High Resolution Chemical Stratigraphies of Atmospheric Depositions from a 4 m Depth Snow Pit at Dome C (East Antarctica)

In this work, we present chemical stratigraphies of two sampling lines collected within a 4 m depth snow pit dug in Dome C during the Antarctic summer Campaign 2017/2018, 12 years after the last reported snow pit. The first sampling line was analyzed for nine anionic and cationic species using Ion Chromatography (IC); the second sampling line was analyzed for seven major elements in an innovative way with Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) after sample pre-concentration, allowing the study of deposition processes of new markers especially related to crustal source. This coupled analysis, besides confirming previous studies, allowed us to investigate the depositions of the last decades at Dome C, enriching the number of the detected chemical markers, and yielding these two techniques complementary for the study of different markers in this kind of matrix. As a result of the dating, the snow layers analyzed covered the last 50 years of snow depositions. The assessment of the accumulation rate, estimated about 9 cm yr−1, was accomplished only for the period 1992–2016, as the eruption of 1992 constituted the only tie-point found in nssSO42− depth profile. Na, the reliable sea salt marker, together with Mg and Sr, mainly arose from marine sources, whereas Ca, Al and Fe originated from crustal inputs. Post-depositional processes occurred on Cl− as well as on NO3− and methanesulfonic acid (MSA); compared to the latter, Cl− had a more gradual decrease, reporting a threshold at 2.5 m for the post-depositional process completion. For NO3− and MSA, instead, the threshold was shallower, at about 1 m depth, with a loss of 87% for NO3− and of 50% for MSA.

On Finding the Right Sampling Line Height through a Parametric Study of Gas Dispersion in a NVB

The tracer gas method is one of the common ways to evaluate the air exchange rate in a naturally ventilated barn. One crucial condition for the accuracy of the method is that both considered gases (pollutant and tracer) are perfectly mixed at the points where the measurements are done. In the present study, by means of computational fluids dynamics (CFD), the mixing ratio NH3/CO2 is evaluated inside a barn in order to assess under which flow conditions the common height recommendation guidelines for sampling points (sampling line and sampling net) of the tracer gas method are most valuable. Our CFD model considered a barn with a rectangular layout and four animal-occupied zones modeled as a porous medium representing pressure drop and heat entry from lying and standing cows. We studied three inflow angles and six combinations of air inlet wind speed and temperatures gradients covering the three types of convection, i.e., natural, mixed, and forced. Our results showed that few cases corresponded to a nearly perfect gas mixing ratio at the currently common recommendation of at least a 3 m measurement height, while the best height in fact lied between 1.5 m and 2.5 m for most cases.

Monitoring Ambient Nitrate Radical by Open Path Cavity Enhanced Absorption Spectroscopy

<p>We described an open-path cavity enhanced absorption spectroscopy (OP-CEAS) technique for ambient measurement of nitrate radical (NO<sub>3</sub>) near 662 nm. Compared with the close type CEAS system with a sampling line, the OP-CEAS is featured with high accuracy due to free of quantifying NO<sub>3 </sub>loss in the sampling line and cavity. Based on a 0.84 m long open path cavity, the effective absorption length of ~5 kilometers is achieved by a coupled high reflectivity mirrors with the reflectivity of 0.99985 at 662 nm. The detection limit of OP-CEAS for NO<sub>3</sub> measurement is 3.0 pptv (2σ) in 30 seconds. The uncertainty is 11.2% and dominated by the cross section of NO<sub>3</sub>. The instrument was successfully applied in a field measurement at low particulate matter (PM) loading condition. As the sensitive would be decreased due to the strong PM extinctions under heavy PM pollution condition, we highlight the feasibility of this OP-CEAS configuration in the field application under the low PM condition, such as the forest region affected by anthropogenic emissions. This technique also appropriates to be expended in the field detection of other reactive trace gases in future studies.</p>

A Test Stand Study on the Volatile Emissions of a Passenger Car Brake Assembly

Brake-related airborne particulate matter contributes to urban emissions in the transport sector. Recent research demonstrated a clear dependence of the number of ultra-fine particles on the disc brake temperature. Above the so-called transition temperature, the number of ultra-fine particles increases dramatically (several magnitudes). As for exhaust emissions, part of the emissions released during braking can be in the volatile fraction. For this reason, a disc brake test stand specifically designed for aerosol research was equipped with three different aerosol sampling instruments: (i) a standard cascade impactor, (ii) a cascade impactor operating at high temperature with a heated sampling line, and (iii) a standard cascade impactor with a thermodenuder. Tests with a brake assembly representative of European passenger vehicles were executed, and the concentration of released airborne particles was determined. The results showed a decrease by several magnitudes in the concentration (in the size range of below 200 nm) using the cascade impactor operating at 180 °C with the sampling line heated to 200 °C. A further decrease in the concentration of airborne particles with size fractions below 200 nm was measured using a standard cascade impactor with a thermodenuder heated to 300 °C.

Modelling of forest decluttering technology along with estimation of deadwood amount

A technology has been proposed for cleaning the forest from deadwood along with an evaluation of its total amount on the site (CFD). The basis of the deadwood quantitative evaluation is the linear intersection sampling (LIS). Within the CFD framework technology, the paper considers the technique of harvesting deadwood using a portable winch with a cable length from 40 to 120 m. A mathematical model has been developed of both the technological process and deadwood estimation. In the model, a number of sites were considered accounting for 50 to 150pcs of deadwood / ha. The results of simulation experiments have showed that the required number of sampling lines decreases in a power-law dependence with an increase in the amount of deadwood on the site and the length of the winch cable (sampling line). For the accuracy index P = 20%, the required number of sampling lines is within the range of 10-70 pcs / ha. Errors between the true values of the deadwood amount on the strip and its estimates did not exceed 7% in absolute value. At the same time, the deviation of the estimates depends neither on the amount of deadwood on the strip nor the length of the winch cable (sampling line). Errors in estimating the mean deadwood length for a sample made from the pieces that crossed sampling lines did not exceed 3%. The estimation procedure impact on the deadwood harvesting productivity proved to be negligible. The drop in performance does not exceed 1%. The impact of the amount of deadwood on the productivity on the site can be considered insignificant. With an increase in the length of the winch cable, a noticeable decrease in productivity is observed. Thus, with an increase in the length of the cable from 40 m to 120 m, productivity drops by 40%. This is due to the fact that the technology in question assumes piece skidding of deadwood. In this case, the time it takes to unwind the cable to a greater distance exceeds the time for the skid relocation. However, should the technology change, for example, in case of using a more powerful winch and skidding several trees at the same time, the situation may change.