Emission of submicron aerosol particles in cement kilns: Total concentration and size distribution.

Cement plants are responsible for particle and gaseous emissions into the atmosphere. With respect to particle emission, the greater part of is in the range from 0.05 to 5.0 µm in diameter. In the last years attention was paid to submicron particles, but there is a lack of available data on the emission from stationary sources. In this paper, concentration and size distribution of particles emitted from four cement kilns, in relationship to operational conditions (especially the use of alternative fuel to coal) of the clinker process are reported. Experimental campaigns were carried out by measuring particles concentration and size distribution at the stack of four cement plants through condensation particle counter (CPC) and scanning mobility particle sizer spectrometer (SMPS). Average total particle number concentrations were between 2000 and 4000 particles/cm³, about 8-10 times lower that those found in the corresponding surrounding areas. As for size distribution, for all the investigated plants it is stable with a unimodal distribution (120-150 nm), independent from the fuel used.

Nitrogen dioxide reductions from satellite and surface observations during COVID-19 mitigation in Rome (Italy).

Lockdown restrictions were implemented in Italy from 10 March 2020 to contain the COVID-19 pandemic. Our study aims to evaluate air pollution changes, with focus on nitrogen dioxide (NO2), before and during the lockdown in Rome and in the surroundings. Significant NO2 declines were observed during the COVID-19 pandemic with reductions of - 50%, - 34%, and - 20% at urban traffic, urban background, and rural background stations, respectively. Tropospheric NO2 vertical column density (VCD) from the TROPOspheric Monitoring Instrument (TROPOMI) was used to evaluate the spatial-temporal variations of the NO2 before and during the lockdown for the entire area where the surface stations are located. The evaluation is concerned with the pixels including one or more air quality stations to explore the capability of the unprecedented high spatial resolution to monitor urban and rural sites from space with relation to the surface measurements. Good agreement between surface concentration and TROPOMI VCD was obtained in Rome (R = 0.64 in 2019, R = 0.77 in 2020) and in rural sites (R = 0.71 in 2019). Inversely, a slight correlation (R = 0.20) was observed in rural areas during the lockdown due to very low levels of NO2. Finally, the TROPOMI VCD showed a sharp decline in NO2, larger in urban (- 43%) than in rural sites (- 17%) as retrieved with the concurrent surface measurements averaging all the traffic and urban background (- 44%) and all the rural background stations (- 20%). These results suggest air pollution improvement in Rome gained from implementing lockdown restrictions.

Study of nitrogen containing compounds in the polar troposphere.

Atmospheric nitrogen compounds play a critical role in tropospheric photochemistry and are crucial to understand the chemical and physical evolution of atmospheric pollutants in polar areas. Measurements of these species in remote areas are rare, although their relevance is well established. Sampling campaigns of gaseous and particulate atmospheric trace species were performed in Arctic and in Antarctica during three consecutive years (1997-1999), using a proper combination of annular denuders and filter pack. After sampling, the ionic species were extracted with aqueous solutions and analysed by means of ion chromatography. Quality assurance on the sampling and analytical steps allowed accurate and precise measurements of all relevant compounds, which are thought to be important to nitrogen chemistry, at very low concentration levels. In addition, the measurements also included a multistage low-pressure impactor for the collection of particulate matter in different size regions (0.035-15.9 mm). Results obtained from these campaigns demonstrate that the minor components may be measured at levels as low as a few nanograms per cubic meter. The reported concentrations are to be considered among the first observations of nitrogen containing compounds in polar sites.