Qualitative VOCs burden and real-time concentrations fluctuations in illegally managed waste landfills by Proton Transfer Reaction Time-of-Flight Mass Spectrometry

Volatile organic compounds (VOCs) comprise only a small amount of the overall emitted landfill gases. However, they can diffuse into the atmosphere affecting tropospheric chemistry and regional air quality, representing a risk for human health. This study aims to investigate the qualitative VOCs burden into biogas and their quantitative variation during a continuous period on a landfill site in the area known as "Terra dei fuochi". In this particular region in Southern Italy, urban waste combined with industrial toxic material has been illegally dumped for decades. In order to obtain a real-time VOCs detection, we used a recently developed Proton Transfer Reaction Time-of-Flight mass spectrometer (PTR-TOF-MS). Ambient air sampling was carried out with an external pump through a heated and coated Teflon sampling line, from the top of a micrometeorological tower located approximately in the middle of four different landfills. On a typical day, ions that passed a signal-to-noise (S/N) filter of 2, are classified and divided in four groups by mass-to-charge (m/z) range: M31-69, M69-136, M136-273 and M273-350. The results have shown that M31-69 group is the most representative range of masses (77%), followed by M69-136 (15%), M136-237 (7%) and M237-350 (1%) groups. Furthermore, hourly average concentrations fluctuations of dominant compounds above S/N=8 are shown, during a week from 20 to 28 July 2016. Amongst these VOCs, toluene, benzene and xylenes show hourly average concentrations in the range 0.06-0.07 ?g/m3, 1.4-4.3 ?g/m3 and 0.07-2.3 ?g/m3, respectively, and a good agreement with mean temperature trend. Monoterpenes, in the range of 0.3-1.3 ?g/m3, seem to follow both mean temperature and humidity trend, with several peaks spread along the whole measurements window, often occurring in the nighttime. This study investigate, for the first time, the qualitative VOCs burden into biogas and their real-time concentration fluctuations in illegally managed waste landfills.