Box-Modelling of O3 and its sensitivity towards VOCs and NOx in Mexico City under altered emission conditions

Abstract

Volatile organic compounds (VOCs) data and other inorganic pollutants, in conjunction with surface meteorological data and planetary boundary layer height (PBLH) were collected at an urban site in Mexico City continuously from 6 to 18 March 2016. The zero-dimensional chemical box model AtChem2 was employed to investigate the in situ O3 generation in Mexico City. This model incorporates a subset of the Master Chemical Mechanism (MCM v3.3.1). AtChem2 was constrained to 29 VOCs, NO, NO2, SO2, HONO, temperature, pressure, relative humidity, PBLH, and photolysis rates (JNO2 as J4 and JO1 as J1). The Tropospheric Ultraviolet (TUV) radiation model, version 5.3, was utilized to calculate the radiation propagation through the atmosphere and determine the photolysis rates of NO2 and O1 in Mexico City. A series of modeling scenarios were conducted to explore how O3 generation responds to variations in VOCs and NOx. VOCs and NOx mixing ratios were adjusted independently, multiplying their mixing ratios by values ranging from 0.1 to 2.0. This variation of VOCs and NOx resulted in distinct model scenarios, allowing us to assess the sensitivity of O3 generation. It revealed that at least this area in Mexico City falls into a NOx limited area with regard to ozone formation. When only NOx is reduced, significant reduction in O3 is observed. While government interventions in Mexico City over the past decades have successfully reduced primary pollutant emissions, still episodes with high O3 levels occur, which require reassessment of O3 abatement strategies.