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 1

• 4-5 Aug. 2004

Case Study 1

• HYSPLIT results• 1.25 km air remained

in study area over

4-5 aug• Some questions

Case Study 2

• 1-2 Sept 2006

• Occurs after a cold front

• Background Effect

Case Study 2

• Land/Sea breeze

Case Study 3

• 5 Oct 2006• 8 hr mean (oct 4)

52.6 ppbv• 1.4-1.8 km interaction

With LFT.

Case Study 4

• 10-11 Aug 2007

• Light winds

• Why no intensification

• Imported O3 and

LFT interactions

Mean Profiles

• Calculating mean

O3 production

• PM profile enhancements

= LFT interaction

Residual Layer

• Fairly High Correlation

• Slightly less max AM O3 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