Assessment of the NOх integral emission from the St.Petersburg megacity by means of mobile DOAS measurements combined with dispersion modelling

Abstract

Megacities are strong sources of environmental pollution. Accurate estimates of the corresponding emissions are important to assess environmental impact and to ensure reliable operation of numerical atmospheric models. One of the most important factors of air pollution in large cities and industrial centers is anthropogenic emission of nitrogen oxides, NOx (= NO + NO2). St. Petersburg is the second largest industrial city in Russia and one of the largest northern megacities in the world. This study aims to experimentally derive the total NOx emission from the metropolitan area of St. Petersburg, based on data from mobile DOAS measurements of NO2 amount. We use data from a series of mobile experiments performed around the city in March and April 2019 and combine them with NO2 field calculations based on HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) simulations. As an initial approximation to a priori information on the spatial distribution of NOx emission sources in the St. Petersburg area, we consider ODIAC (Open-source Data Inventory for Anthropogenic CO2) data. Based on fitting the HYSPLIT simulation results to our mobile DOAS (Differential Optical Absorption Spectroscopy) measurements, and applying some assumptions about the daily, weekly and seasonal cycles of urban anthropogenic pollution, we obtained an experimental estimate of total NOx emissions of 77 ± 27 kilotons in 2019. Moreover, we managed to obtain an estimate of the contribution of urban thermal power plants to the total NOx emissions, which amounting to ∼28%.