Measurements of Formaldehyde Fluxes in Houston, Texas
1
Yelden ,
2
Mount ,
2
Spinei
Tracy
George
Elena
1. Department of Physics, Central College
2. Dept. of Laboratory for Atmospheric Research, Washington State University
Analysis:
•Compared UCLA and WSU raw data (e.g. 8° elevation)
flux [HCHO] in metric tons/day
60
40
20
0
-20
-5
-60
6
4
2
0
4/29/2009
5/3/2009
5/7/2009
5/11/2009
5/15/2009
12:00 PM
5/5/2009
UTC = local standard time + 6h
4/29/2009
5/3/2009
5/7/2009
5/11/2009
UTC = local standard time + 6h
15
3:00 PM
6:00 PM
9:00 PM
12:00 AM
5/6/2009
UTC = local standard time + 6h
Graph 4: Flux vs. time at angles
5-15° elevation (viewing west)
Graph 5: Flux vs. time at angles
5-15° elevation (on May 5th)
The above graphs show the fluxes for VZA 75-85°. From
these graphs, we can see that the fluxes cluster around two
metric tons per day.
•Found differences in HCHO slant column density
(downwind minus upwind)
UCLA_inter_82_90
WSU_SlColCH2O_82_90
difference_82_90
8.0
7.0
flux [HCHO] in metric tons/day
60x10
f85_270
f84_270
f83_270
f82_270
f81_270
f80_270
f75_270
8
-2
4/25/2009
Graph 1: UCLA and WSU raw data vs. time at 8° elevation angle
40
20
0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
-1.0
-2.0
-3.0
-20
flux_all_east_smoo
flux_all_west_smoo
flux_all_east
flux_all_west
-4.0
-5.0
east viewing
12:00 PM
5/5/2009
3:00 PM
6:00 PM
9:00 PM
4/26/2009
12:00 AM
5/6/2009
VZA: 70-85°
UTC = local standard time + 6h
Graph 2: UCLA and WSU’s data with the difference vs. time at
8° elevation
• Used wind speed and direction data for each observed
angle to compute fluxes in a box model
W_SPD_m_s_
W_DIR_deg_
12
200
6
150
4
100
2
3.2
50
2.8
flux_all_west
flux_all_west_51pt boxcar
flux_all_east
flux_all_east_51pt boxcar
2.4
2.0
1.6
1.2
0.8
0.4
0.0
-0.4
-0.8
-1.2
-1.6
4/29/2009
5/3/2009
5/7/2009
5/11/2009
The above graph shows the span of the fluxes at different
angles. The red indicates fluxes west of the site, whereas the
blue are east of the site. The average flux of HCHO is 1.8 metric
ton per day (+/- 50% because of our assumptions).
3.6
250
8
5/6/2009
Graph 6: Fluxes from VZA 70° through 85° viewing both east and west
vs. time for the entire campaign
300
10
5/1/2009
UTC = local standard time + 6h
"local" I0 reduction
350
Wind Direction (degrees)
Wind Speed (m/s)
0
-40
4/25/2009
5/11/2009
UTC = local standard time + 6h
Graph 3: Wind speed and direction vs. time
• Each site had a multi-axis differential absorption
spectrometer (MAX-DOAS)
- Used scattered sunlight as a light source to
measure the UV spectrum and deduce the slant
column density of HCHO
- Determined slant column densities [molecules/cm^2]
as a function of time at various elevation angles in
east and west directions
- Each instrument scanned the sky at the same angle
and similar time approximately perpendicular to the
mean wind direction.
5
-10
0
MAX-DOAS Schematic
10
flux [HCHO] in metric tons/day
Slant Column Density (molecules/cm^2)
UCLA_inter_82_90
WSU_SlColCH2O_82_90
15
4/25/2009
•To determine the HCHO fluxes in Texas City from industrial
sources
•To understand the production of HCHO in the area
•To contribute to models of the effects these industrial
emissions have on the formation of ozone
The UCLA site was
located upwind and
south of the plants;
WSU was on the
north end and
downwind
80x10
east viewing
Objectives:
Field Methods:
f85_270
f84_270
f83_270
f82_270
f81_270
f80_270
f75_270
15
Slant Column Density (molecules/cm^2)
Formaldehyde (HCHO) is a chemical compound that has
adverse effects on human health and can increase urban
ozone levels significantly. Ozone is regulated by the US
EPA; the Houston area is often in violation of those
standards. Sources of formaldehyde include direct
emissions from vehicles, emissions from petrochemical
plants, and photochemical production. As part of the
Study of Houston Area Radical Species (SHARP) campaign
organized by the Houston Advanced Research Consortium
(HARC), Washington State University (WSU) and University
of California – Los Angeles (UCLA) worked together to
collect formaldehyde flux data in Texas City near three oil
refineries processing approximately one million barrels of
oil per day. The measurements were collected from April
15 - May 31, 2009.
Results:
flux [HCHO] in metric tons/day
Introduction:
• Formulate box model equation:
Assumptions that contribute to errors:
- Uniform emissions from the refineries
• Test site was approximately 5 km x 2 km
- HCHO is uniformly mixed vertically
- No aerosol loading; however, aerosol loading was
very large most of the time
- Planetary Boundary Layer height (PBL) = 700m
• From LIDAR boundary layer measurements
d = H/ cos(VZA)
VZA = viewing zenith angle
H = PBL height
L = distance (South to North)
of test site
W = width of industrial site
U = wind speed
Flux = metric tons/day
Box model equation used:
•Determined average fluxes east and west of the test site
12:00 PM
4/29/2009
VZA: 70-85° "local" I0 reduction
3:00 PM
6:00 PM
9:00 PM
UTC = local standard time + 6h
12:00 AM
4/30/2009
Graph 7 shows how the fluxes
sometimes peak around noon
local time. This might also
suggest secondary formation
of HCHO in the atmosphere
due to photolysis.
Graph 7: A randomly selected day to
show the east and west fluxes vs. time
Conclusion:
From these calculations, we determined that the three major
refineries in the area produce, either directly or secondary, about 630
metric tons/year of formaldehyde. This is 15% of the total VOC
emissions reported by the largest of the three refineries. Therefore,
the total HCHO emissions are less than 15% of the total VOC
emissions. Since formaldehyde is one contributor to the formation of
ozone, this study will provide vital information to those who regulate
regional air quality. Monitoring formaldehyde produced in the
Houston area would be useful in understanding ozone production and
improving air quality in the region.
We plan to identify and use a standardized I0, instead of a local I0
that was used in these preliminary results, which will likely increase
these fluxes by a small amount.
Acknowledgements:
We would like to thank the Houston Advanced Research Consortium
(HARC) for organizing the Study of Houston Area Radical Species (SHARP)
campaign. We would also like to thank the University of California–Los Angeles
(UCLA) for their help in collecting and analyzing the data.
This work was supported by the National Science Foundation’s REU
program under grant number 0754990 and HARC grant H104A.