1. Measurements of Trace Gases at the Manvel Croix and Galveston Sites during DISCOVER-AQ
Paul Kelley1,2, Winston Luke2, Xinrong Ren1,2
1Dept of Atmos. & Oceanic Sci., Univ. of Maryland
2NOAA Air Resources Laboratory
Objectives:
Measurements of trace gases at the two sites in support of DISCOVER-AQ
Comparison of surface measurements with aircraft profiling observations
Ozone production efficiency using the correlation between O3 and NOz

2. Surface Measurements at Manvel-Croix and Galveston
NOAA: 3-channel NO/NO2/NOY, O3 and SO2.
TCEQ: O3, NO/NOx and Met
Located to SSE of Texas City and SW of downtown Galveston and the Port of Galveston
NOAA: NO2 based on Cavity Ring Down
TCEQ: O3, NO/NOx and Met
Located to S of downtown Houston and SW of the Houston Ship Channel

3. Diurnal [NO2] Variation at Manvel Croix
Ranged from close to zero to 29 ppbv (10-sec data)
Typical day-to-day variations with peak during morning rush hour.
Max. [NO2] of 11 ppbv at 7:00-8:00 CST.
Min. [NO2] of 1-2 ppbv in the afternoon
Slightly increasing in early evening: lower boundary heights?

4. Elevated [NO2] at Manvel Croix
High [NO2] in the winds from NE & N.
Elevated [NO2] in almost all directions: suggesting nearby local emissions.

5. NO2 at Manvel Croix and Comparison with the P-3
General good agreement
Limit P-3 data at Manvel Croix:
(1) below 600 m (2000 ft)
(2) within +/-0.02˚ Lat/Long of the site
P3 CL: chemiluminescence
P3 LIF: laser induced fluorescence

6. P-3 [NO2] vs. surface [NO2] at Manvel Croix
Fraction
of day
Fraction
of day
Good agreement in general
More scattered at lower [NO2] later in the day

7. P-3 [O3] vs. surface [O3] at Manvel Croix
Fraction
of day
Very good agreement with little dependence on time of day.

8. P-3 [O3] vs. surface [O3] at Galveston
Fraction
of day
Limit P-3 data at Galveston :
(1) below 300 m (1000 ft)
(2) within +/-0.02˚ Long/Lat of the site
Good agreement with little dependence on time of day.

9. P-3 [NO2] vs. surface [NO2] at Galveston
Fraction
of day
Reasonable agreement in general.
More scattered than Manvel Croix: more horizontal/vertical gradients due to the location of the site.

10. Wind dependence of [NOY] and [SO2] at Galveston
Highest [NOY] and [SO2] were observed in the winds from NNE , where downtown Galveston and the Port of Galveston are located.

11. Galveston: [NOZ] (= [NOY] – [NOX])
Peak NOz (~1.2 ppb) in the afternoon  photochemical formation.
Nighttime NOz levels: relatively constant (~ ppbv).

12. Galveston: Ox (=O3+NO2) vs. NOz
During daytime: 10am-6pm (CST)
About 16 ppb O3 is created when 1 ppb NOx converted to NOy.
During DAQ-Baltimore/Washington 2011, this number is ~5-6.
Data collected from 10am to 6pm (CST) at the surface
Specific for mean transport times from the emission source regions to Galveston
Assuming minimal depositional loss of NOY species such as HNO3.
Similar slopes (14-16) using the P-3 data during the spirals at Galveston and Smith Point.

13. Summary
High NO2 levels at Manvel Croix were influenced by plumes from downtown Houston and the Houston Ship Channel.
Trace gases at Galveston: relatively low levels, but influenced by pollution plumes.
Comparisons with the P-3 data: good agreement at Manvel Croix and more scattered at Galveston.
Estimated ozone production efficiency of ~16 ppb O3/ppb NOx conversion at Galveston: a factor of 2-3 larger than that during DISCOVER-AQ 2011 in the Baltimore-Washington area.

14. Acknowledgements AQRP & TCEQ for support
Jim Thomas, Vince Torresm, and Raj Nadkarni for logistic support
Dave Sullivan and Maria Stanzione for project management support
The P-3 science team for use of the aircraft data
Mark Estes for providing the TCEQ data
Russ Dickerson for loaning instrument supported by AQAST