An Evaluation of the Influence of the Morning Residual Layer on Afternoon Ozone Concentrations in Houston Using Ozonesonde Data

Introduction The Houston-Galveston-Brazoria area (HGBR) is noted for its violations of EPA NAAQS > 220 Ozonesondes were launched during Houston, TX as part of TexAQS II and IONS-06 Where do polluted airmasses come from What effect do local meteorological conditions have on air quality Where will polluted air travel after leaving HGBR

HGBR Area Map

Boundary Layer Evolution Convective (daytime) and stable (nighttime)

Boundary Layer Characteristics The Nocturnal Boundary Layer: –Stable (upward heat flux) –Shallow (100s of meters) –Residual layer (RL) above NBL –RL height – Identified by capping inversion and RH decrease. –RL often retains characteristics of previous day’s mixing layer

Boundary Layer Characteristics Convective Boundary Layer –Unstable –Typically 1000s of meters –Has a large “mixed layer” –Mixed layer height - 4 ways to find it

Boundary Layer Pollution Effects RL can act as trace gas “reservoir” “reservoir” effect depends on (shear) turbulence eddies can cause mixing. Land and sea breeze

Case Study Aug. 2004

Case Study 1 HYSPLIT results 1.25 km air remained in study area over 4-5 aug Some questions

Case Study Sept 2006 Occurs after a cold front Background Effect

Case Study 2 Land/Sea breeze

Case Study 3 5 Oct hr mean (oct 4) 52.6 ppbv km interaction With LFT.

Case Study Aug 2007 Light winds Why no intensification Imported O 3 and LFT interactions

Mean Profiles Calculating mean O 3 production PM profile enhancements = LFT interaction

Residual Layer Fairly High Correlation Slightly less max AM O 3 than the day before Removal of several outliers due to changing synoptic conditions leads to higher correlation

Residual Layer and Afternoon O3 concentration Compare RL ozone to afternoon ozone Compare Previous day 8 hr average to afternoon ozone

END