An analysis of the relationship between the planetary boundary layer and surface level ozone concentrations in Phoenix, Arizona

This study examines the linkage between surface level ozone and planetary boundary layer meteorological variables in the Phoenix Metropolitan region during the summer North American Monsoon period for years 2010 through 2020. Data used in this study was obtained and derived from both 1200 UTC radiosonde observations launched from the Phoenix National Weather Service office, and 8-hour average ozone concentration measurements from Maricopa County monitoring stations. Specific boundary layer meteorological variables examined in this study included inversion temperature, mixing level pressure, mixing level height, and the surface level variables of temperature, dew point temperature, pressure, wind speed, and meridional and zonal wind directions. The daily maximum, 8-hour average ozone concentrations among all Maricopa County monitoring stations were used in this study. To determine ozone’s linkage to meteorological variables, normality tests, determination of Pearson product moment correlation coefficient and/or the Spearman rank correlation coefficient, and the discriminative Student’s two-sided t-test statistic between ozone exceedance and non-exceedance days were used. Statistically significant coefficients indicate weak negative correlations between surface level ozone and surface level pressure, and mixing level pressure, and weak positive correlations between surface level ozone and surface level temperature, surface level zonal wind direction, mixing level height, and inversion temperature. These correlations were linear for surface level pressure, surface level temperature, and inversion temperature. The two-sided Student’s t-test statistic indicates a significant difference in the mean on ozone exceedance and non-exceedance days for surface level temperature, and the upper-air variables of mixing level height, mixing level pressure, and inversion temperature. Both correlations and differences in the mean of upper-air variables showed statistically significant results. These findings suggest that further research should be completed to determine the forecasting ability of morning sounding analyses on surface level ozone in locations exhibiting similar emissions and geographic features as the Phoenix Valley.