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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