Meteorological detrending of long-term (2003-2017) ozone and precursor concentrations at three sites in the Houston Ship Channel Region

Abstract

Ambient ozone is influenced by meteorology in addition to concentrations of precursor compounds (oxides of nitrogen (NOx) and volatile organic compounds (VOC)). The efficacy of regulatory measures in nonattainment areas, such as the Houston-Galveston-Brazoria (HGB) area of Texas, can be efficiently evaluated by separating the meteorologically induced variability from ozone data. This study applies the Kolmogorov-Zurbenko (KZ) filter for obtaining a temporal resolution of ozone, NOx and VOC data into short-term, seasonal and long-term components, at three stations located near the Houston Ship Channel. Air quality and meteorological data for Clinton (AQS Site ID: 48-201-1035), Deer Park (48-201-1039) and Lynchburg Ferry (48-201-1015) stations were analyzed for the period between 2003 and 2017. A combination of KZ filter and multiple linear regression, with predictor variables (solar radiation, temperature, dew point, and wind speed) is employed to develop meteorologically independent ozone, NOx and VOC trends. This study indicates that variability from meteorology accounts for 51%, 35% and 41% in baseline MDA8 ozone at Clinton, Deer Park, and Lynchburg stations, respectively. For the 15-year study period, long-term MDA8 ozone trends for Deer Park and Lynchburg stations were decreasing at a linear rate of 0.689 ± 0.016, and 0.573 ± 0.019 ppb/yr, respectively. At the Deer Park and Lynchburg stations, a high degree of correlation for meteorologically detrended MDA8 ozone with NOx (ρ: 0.899, 0.678) and VOC (ρ: 0.912) concentrations was observed. For the Clinton station, decreases in NOx and VOC levels d at the rate of 2.068 ± 0.032 ppb/yr and 14.637 ± 0.412 ppb C/yr, were not reflected in MDA8 ozone, which showed no discernable decrease over the 15 years. The regional transport of ozone plumes from the east and south-east directions of the Clinton station were identified as the likely factors for this pattern. Implications: The efficacy of emission control policies in the Houston-Galveston-Brazoria area can be evaluated by isolating the meteorological forcing from air quality time series data and developing long-term trends for ozone and precursor compounds. This paper applies the Kolmogorov–Zurbenko filter technique in combination with Multiple Linear Regression analysis to MDA8/MDA1 ozone, NOx, and VOC data between 2003-2017 at three air monitoring stations near the Houston Ship Channel. Estimates for trends of air quality are calculated and underlying causes are investigated to provide a guidance for further investigation into air quality management of the Greater Houston Area.