Temporal variations of black carbon, carbon monoxide, and carbon dioxide in Mexico City: Mutual correlations and evaluation of emissions inventories

Abstract

Black carbon (BC), carbon monoxide (CO), and carbon dioxide (CO2) were measured in Mexico City (UNAM observatory) with a Photoacoustic Extinctiometer-PAX (BC) and a Cavity Ring-Down Spectroscopy analyzer-CRDS (CO and CO2), from November 2014 to July 2016. The objective of this study was to determine temporal variations of BC, CO, and CO2, their mutual correlations, and evaluation of the Mexico City emission inventory. The highest concentrations of pollutants were detected in cold dry season. The average concentrations of BC, CO, and CO2, for the entire period, were 2.95 μg m−3, 0.64 ppm, and 421.81 ppm, respectively. We calculated ΔBC/ΔCO, ΔBC/ΔCO2, and ΔCO/ΔCO2 using three methods to obtain a confidence interval for the emission ratios. BC, CO, CO2 concentrations, and the ΔBC/ΔCO ratio were maximum in the early morning, while the ΔBC/ΔCO2 and ΔCO/ΔCO2 peak was maximum in the afternoon. BC and CO have a weekday/weekend difference. The estimated slopes (ΔBC/ΔCO, ΔBC/ΔCO2, and ΔCO/ΔCO2) were compared with the emission ratios (BC/CO, BC/CO2, and CO/CO2) derived of the 2016 Mexico City emissions inventory. For mobile sources, the emission ratios of BC/CO and BC/CO2 were within the measurement range of ΔBC/ΔCO and ΔBC/ΔCO2, while CO/CO2 was underestimated in the emission inventory.