From rural to urban areas: a transect along the Greve River Basin (Chianti territory, Central Italy) investigating greenhouse gases distribution and metal deposition with a combination of traditional and low-cost technical approaches

The adverse impact of human activities on the air quality is largely related to the use of fossil fuels and intensive agricultural exploitation, which cause the emissions in the air of a wide variety of climate-changing species and harmful gaseous, liquid and solid pollutants. Moreover, atmospheric particulate matter may affect soils, biota, and waters through wet and dry deposition. Therefore, the management of air quality is an impelling issue to limit damages and protect human and environmental health. This study presents the results of a geochemical survey carried out in a study area of relevant hydrological, economic, and socio-cultural interest: the Greve River Basin (Chianti territory, Italy). The Greve River is a tributary of the Arno River and extends about 50 km south of Florence. The upstream side (845 m a.s.l.) is dominated by vineyards and olive trees, whilst downstream (45 m a.s.l.) several urban and industrial areas occur. The survey was led from May to September 2022 by adopting two measuring strategies: (i) along transepts, deploying a mobile station equipped with a Picarro G2201-i analyzer to measure CO2 and CH4 concentrations and δ13C-CO2 and δ13C-CH4 values (‰ vs. V-PDB) by Cavity Ring-Down Spectroscopy; and (ii) at five fixed stations, measuring CO2, CH4, PM2.5 concentrations, as well as air temperature and relative humidity, using low-cost multiparametric instrumental prototypes, coupled with atmospheric deposition and rain samplers to collect particulate samples for chemical lab analysis. The CO2 and CH4 sensors have been calibrated in-field based on parallel measurements with the Picarro G2201-i and elaborating the calibration data with a machine learning-based algorithm. The measurements along the transepts, combined with the monitoring at the fixed stations, showed that the downstream areas were affected by the highest concentrations of CO2 and CH4, with isotopic signatures revealing an origin of these gases mainly due to vehicular traffic. The distribution of these air contaminants reflected the evolution of the Planetary Boundary Layer, with higher concentrations during the early morning, when gas accumulation occurred due to stable atmospheric conditions, and lower concentrations during daytime for the establishment of convective turbulences favoring the dispersion of contaminants. The distribution of particulate was consistent with that of the gaseous species, and the main sources were clearly distinguished based on the chemical composition of the depositions at the fixed stations. The downstream sites displayed anomalies in the Traffic Related Elements (e.g., Pb, Ni, Cd, Zn, As, etc.), whilst the upstream site was enriched in Cu and Se, possibly due to the use of fertilizers and pesticides. The promising results from the present study could result in an affordable approach to effectively improve air quality monitoring strategies and support data-driven policy actions to reduce pollutant emissions.