Use of Combined Observational- and Model-Derived Photochemical Indicators to Assess the O3-NOx-VOC System Sensitivity in Urban Areas

Abstract

Tropospheric levels of O 3 have historically exceeded the official annual Mexican standards within the Monterrey Metropolitan Area (MMA) in NE Mexico. High-frequency and high-precision measurements of tropospheric O 3 , NO y , NO 2 , NO, CO, SO 2 , PM 10 and PM 2.5 were made at the Obispado monitoring site near the downtown MMA from September 2012 to August 2013. The seasonal cycles of O 3 and NO y are driven by changes in meteorology and to a lesser extent by variations in primary emissions. The NO y levels were positively correlated with O 3 precursors and inversely correlated with O 3 and wind speed. Recorded data were used to assess the O 3 -Volatile Organic Compounds (VOC)-NO x system's sensitivity through an observational-based approach. The photochemical indicator O 3 /NO y was derived from measured data during the enhanced O 3 production period (12:00-18:00 Central Daylight Time (CDT), GMT-0500). The O 3 /NO y ratios calculated for this time period showed that the O 3 production within the MMA is VOC sensitive. A box model simulation of production rates of HNO 3 (P HNO3 ) and total peroxides (P perox ) carried out for O 3 episodes in fall and spring confirmed the VOC sensitivity within the MMA environment. No significant differences were observed in O 3 /NO y from weekdays to weekends or for P HNO3 /P perox ratios, confirming the limiting role of VOCs in O 3 production within the MMA. The ratified photochemical regime observed may allow the environmental authorities to revise and verify the current policies for air quality control within the MMA.

Observed trends in ground-level O<sub>3</sub> in Monterrey, Mexico, during 1993–2014: comparison with Mexico City and Guadalajara

“…It is clear that shortrange transport and large upwind emissions of O 3 precursors from the industrial area dominate the MMA (SEMARNAT, 2006(SEMARNAT, , 2011(SEMARNAT, , 2014SDS, 2015). This is underlined at OBI with the highest values of O x where the predominant wind direction is NE, consistent with the transport of emissions from the industrial area located to the NE and photochemical processing of air masses (Carrillo-Torres et al, 2017). The daily cycles of O 3 determined within the MMA are consistent with those reported for Los Angeles (VanCuren, 2015) and Toronto (Pugliese et al, 2014).…”

Associations among air pollutants, grass pollens, and daily number of grass pollen allergen‐positive patients: a longitudinal study from 2012 to 2016

“…In contrast, the monthly concentration of O 3 showed the opposite trend, increasing in February and peaking during May and June. Because O 3 is the primary component of photochemical oxidants, the high concentration of O 3 in summer may be related to the high solar ultraviolet radiation intensity and high temperature in summer, which results in so‐called “summer smog.” Indeed, studies have suggested that the concentrations of NO x and O 3 are negatively correlated, which would be consistent with the findings of the present study.…”

Spatial and Temporal Distribution of PM2.5 Pollution over Northeastern Mexico: Application of MERRA-2 Reanalysis Datasets

“…In spring, the lower relative humidity-compared to other seasons and relatively strong atmospheric dispersion-may have enhanced the correlation between AOD and PM 2.5 [79]. Similar meteorological conditions in the MMA were reported by Carrillo Torres et al (2017) [80] and Mancilla et al (2015) [43].…”