Mobile measurements of ground-level methane concentrations near solid waste landfills

In Russia, landfill disposal is the main method of municipal solid waste (MSW) disposal, which, in the absence of a separate waste collection system and its preliminary mechanical processing, poses a threat to the environment and public health. Since the complete decomposition of organic matter contained in municipal waste requires decades, such landfills remain sources of emissions of the so-called landfill gas, more than half of which consists of methane, for a long time. Objective monitoring of methane emissions is complicated by its high spatial heterogeneity over the surface of landfills, which can lead to significant errors in estimates of the total methane flow obtained on the basis of direct measurements using the chamber method.

In April 2001 and 2024, the authors carried out specialized measurement campaigns to study greenhouse gas (CO2 and CH4) fluxes from the territory of St. Petersburg, based on direct measurements of ground-level concentrations from a moving vehicle. The measurements were carried out along a closed route of the Ring Road (KAD), which bypasses most of the city's anthropogenic emission sources. These detours were aimed at assessing the integrated emissions of the gases under study from the city using the mass balance method. The preliminary result of the measurement data analysis revealed a stable maximum of the ground-level methane concentration, significantly exceeding its average level along the entire length of the KAD and localized near one of the largest city solid waste landfills ("Novosyolki"). The measurement data reveal local maxima of methane concentration on sections of the route downwind from the landfill. The maximum values ​​recorded from a vehicle in this observation area reached ~9 ppmv, which significantly exceeds the background ground-level methane concentration of ~2 ppmv. Average nighttime and morning peak concentrations (~5.0 ppmv) are noticeably higher than daytime and evening ones (~2.3 ppmv). Numerical modeling of landfill gas air dispersion, performed using a dispersion model and taking into account the characteristics of atmospheric stability during the observation period, demonstrated qualitative agreement between the calculated ground-level methane concentrations and the experimental data. Based on a comparison of the measurement results with the modeling data for the air pollution plume from the landfill territory, methane emission estimates were obtained amounting to ~640±420 kg/hour in April 2021 and ~200±90 kg/hour in April 2024. The observed significant reduction in emissions from 2021 to 2024 is consistent with official information on the closure of the landfill in 2018 and the start of landfill cover and reclamation work, which continues to this day. Emissions from the territory of one Novosyolki landfill may account for ~10% of the total anthropogenic methane emissions from the territory of St. Petersburg.

Along with measurements on the ring road route, a series of ring measurements were carried out in June 2024 around another municipal solid waste landfill, Novy Svet. Preliminary estimates of methane emissions from the territory of the currently operating landfill were obtained.

The study was carried out using equipment of the Center for Geo-Environmental Research and Modeling (GEOMODEL) of the Research park of St.Petersburg State University, and funded by a grant from the Russian Science Foundation (project No. 24-27-00033).