Variability of winter and summer surface ozone in Mexico City on the intraseasonal timescale

Abstract

Abstract. Surface ozone concentrations in Mexico City frequently exceed the Mexican standard and have proven difficult to forecast due to changes in meteorological conditions at its tropical location. The Madden-Julian Oscillation (MJO) is largely responsible for intraseasonal variability in the tropics. Circulation patterns in the lower and upper troposphere and precipitation are associated with the oscillation as it progresses eastward around the planet. It is typically described by phases (labeled 1 through 8), which correspond to the broad longitudinal location of the active component of the oscillation with enhanced precipitation. In this study we evaluate the intraseasonal variability of winter and summer surface ozone concentrations in Mexico City, which was investigated over the period 1986-2014 to determine if there is a modulation by the MJO that would aid in the forecast of high-pollution episodes.Over 1 000 000 hourly observations of surface ozone from five stations around the metropolitan area were standardized and then binned by active phase of the MJO, with phase determined using the real-time multivariate MJO index. Highest winter ozone concentrations were found in Mexico City on days when the MJO was active and in phase 2 (over the Indian Ocean), and highest summer ozone concentrations were found on days when the MJO was active and in phase 6 (over the western Pacific Ocean). Lowest winter ozone concentrations were found during active MJO phase 8 (over the eastern Pacific Ocean), and lowest summer ozone concentrations were found during active MJO phase 1 (over the Atlantic Ocean). Anomalies of reanalysis-based cloud cover and UV-B radiation supported the observed variability in surface ozone in both summer and winter: MJO phases with highest ozone concentration had largest positive UV-B radiation anomalies and lowest cloud-cover fraction, while phases with lowest ozone concentration had largest negative UV-B radiation anomalies and highest cloud-cover fraction. Furthermore, geopotential height anomalies at 250 hPa favoring reduced cloudiness, and thus elevated surface ozone, were found in both seasons during MJO phases with abovenormal ozone concentrations. Similar height anomalies at 250 hPa favoring enhanced cloudiness, and thus reduced surface ozone, were found in both seasons during MJO phases with below-normal ozone concentrations. These anomalies confirm a physical pathway for MJO modulation of surface ozone via modulation of the upper troposphere.

Experience from Integrated Air Quality Management in the Mexico City Metropolitan Area and Singapore

“…Larger-scale meteorology influences surface O 3 concentrations. Barret and Raga [69] observed that the intraseasonal variability of surface O 3 , in both summer and winter, is driven by the variability in the cloud cover due to the upper-troposphere circulation modulated by the Madden-Julian oscillations (MJO). Also, stratospheric O 3 intrusions into the boundary layer were identified by Barret et al [70] during a stratosphere-troposphere exchange event linked to changes in the subtropical jet stream.…”

A Multiscale Analysis of the Tropospheric and Stratospheric Mechanisms Leading to the March 2016 Extreme Surface Ozone Event in Mexico City

“…The zonal jet extension occurred possibly due to the mechanism proposed by Weickmann and Berry (, ): a very active Madden‐Julian Oscillation event traversed the Maritime Continent and Western Pacific in February 2016 (leading to a strengthening of the subtropical jet in early March), which then transitioned into the Western Hemisphere and Indian Ocean the first week of March 2016 (leading to an increase in jet waviness after 07 March 2016). This physical mechanism is supported by Barrett and Raga (), who noted that high surface O 3 concentrations in Mexico City tend to be favored on days when the Real‐time Multivariate Madden‐Julian Oscillation (Wheeler & Hendon, ) index is in phases 2 and 3, which it was from 09 to 13 March 2016. Second, the subtropical jet became baroclinically unstable and wavy. Third, one of those waves, a pronounced anticyclonic ridge along 150°W, underwent anticyclonic wave breaking between 35 and 45°N. Fourth, that wave breaking led to the development of an anomalously deep and equatorward cutoff low between 15 and 25°N. Fifth, the deep low brought O 3 ‐rich stratospheric air well into the troposphere via a pronounced STE event seen in vertical profiles of both PV and O 3 concentration in the air column above Mexico City. This O 3 ‐rich air remained in the air column on 11 and 12 March 2016, likely mixing to the surface on those days and re‐entraining into the ABL due to basin‐wide mesoscale circulations on 13 March 2016. Sixth, subsidence behind the low both suppressed the development of convective clouds and led to the formation of strong thermal inversions near 650 hPa.…”

“…The zonal jet extension occurred possibly due to the mechanism proposed by Berry (2007, 2009): a very active Madden-Julian Oscillation event traversed the Maritime Continent and Western Pacific in February 2016 (leading to a strengthening of the subtropical jet in early March), which then transitioned into the Western Hemisphere and Indian Ocean the first week of March 2016 (leading to an increase in jet waviness after 07 March 2016). This physical mechanism is supported by Barrett and Raga (2016), who noted that high surface O 3 concentrations in Mexico City tend to be favored on days when the Real-time Multivariate Madden-Julian Oscillation (Wheeler & Hendon, 2004) index is in phases 2 and 3, which it was from 09 to 13 March 2016. 2.…”

Ground-based remote sensing of O<sub>3</sub> by high and medium resolution FTIR spectrometers over the Mexico City basin

“…Any comparison study has to consider these fast changing O 3 concentrations and we only compare data that are measured within the same hour. A discussion on O 3 boundary layer variability of Mexico City on time scales beyond the diurnal time scale is given in Barrett and Raga (2016).…”