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

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 mu g m(-3), 0.64 ppm, and 421.81 ppm, respectively. We calculated Delta BC/Delta CO, Delta BC/Delta CO2, and Delta CO/Delta CO2 using three methods to obtain a confidence interval for the emission ratios. BC, CO, CO2 concentrations, and the Delta BC/Delta CO ratio were maximum in the early morning, while the Delta BC/Delta CO2 and Delta CO/Delta CO2 peak was maximum in the afternoon. BC and CO have a weekday/weekend difference. The estimated slopes (Delta BC/Delta CO, Delta BC/Delta CO2, and Delta CO/Delta CO2) 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 Delta BC/Delta CO and Delta BC/Delta CO2, while CO/CO2 was under-estimated in the emission inventory.

Automated summary

The study in Mexico City measured black carbon, carbon monoxide, and carbon dioxide concentrations, finding that pollutants were highest in the cold dry season with maximum concentrations in the early morning. Emission ratios Delta BC/Delta CO and Delta BC/Delta CO2 showed differences between weekdays and weekends. Additionally, emission ratios for BC/CO and BC/CO2 from mobile sources matched the measured values, while CO/CO2 was underestimated in the emission inventory.