Observations are presented which substantiate the hypothesis that significant vertical exchange of ozone and aerosols occurs between the mixed layer and the free troposphere during cumulus cloud convective activity. The experiments utilized the airborne Ultra-Violet Differential Absorption Lidar (UV-DIAL) system. This system provides simultaneous range resolved ozone concentration and aerosol backscatter profiles with high spatial resolution. Evening transects were obtained in the downwind area where the air mass had been advected. Space-height analyses for the evening flight show the cloud debris as patterns of ozone typically in excess of the ambient free tropospheric background. This ozone excess was approximately the value of the concentration difference between the mixed layer and free troposphere determined from independent vertical soundings made by another aircraft in the afternoon

Brewer, D. A.

Browell, E. V.

Ching, J. K. S.

Shipley, S. T.

English

NASA Technical Reports Server

General Disclaimer 
One or more of the Following Statements may affect this Document 
 
 This document has been reproduced from the best copy furnished by the 
organizational source. It is being released in the interest of making available as 
much information as possible. 
 
 This document may contain data, which exceeds the sheet parameters. It was 
furnished in this condition by the organizational source and is the best copy 
available. 
 
 This document may contain tone-on-tone or color graphs, charts and/or pictures, 
which have been reproduced in black and white. 
 
 This document is paginated as submitted by the original source. 
 
 Portions of this document are not fully legible due to the historical nature of some 
of the material. However, it is the best reproduction available from the original 
submission. 
 
 
 
 
 
 
 
Produced by the NASA Center for Aerospace Information (CASI) 
https://ntrs.nasa.gov/search.jsp?R=19850014958 2020-03-20T18:23:15+00:00Z
PB85-144137
Cumulus Cloud Venting of
Mixed Layer Ozone
(U.S.) Environmental Protection Agency
Research Triangle Park, NC
Jan 85
V.S.Dowbow of CNEWC!
Ned 0 Tedw" b0affu6n Swvica
i
it
PB85-144137
EPA-600JD-84-299
January 1985
CUMULUS CLOUD VENTING OF MIXED LAYER OZONE
by
J.K.S. Ching
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
S.T. Shipley and E.V. Browell
National Aeronautics and Space Administration
Langley Research Center
Hampton, VA 23665
and
D.A. Brewer
Systems and Applied Sciences Corp.
Hampton, VA 23666
7
ATMOSPHERIC SCIENCES RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NC 27711
REPRODUCED BY
NATIONAL TECHNICAL
INFORMATION SERVICE
U.S. DEPARTMENT OF COMMERCE
SPRINGFIELD, VA. 22161
1._..._	 ..._...
TECHNICAL REPORT DATA(Please reed Ixuructions on the reverse before completing)
1. REPORT NO. 2. 3. RECIPIENT'S ACCESSIOMNO.
EPA-600/D-84-299 PB85-144137
4. TITLE AND SUBTITLE 6. REPORT DATE
January 1985
CUMULUS CLOUD VENTING OF MIXED LAYER OZONE 6. PERFORMING ORGANIZATION CODE
7. AUTHOR(°` 8. PERFORMING ORGANIZATION REPORT NO.
J.K.S. C)ing, S.T. Shipley, E.V. Browell and D. A. Brewer
9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT NO.
CDWAIA/02 (Task 1324)
11. CONTRACT70 RANTNO.
(same as 12.)
12. SPONSORING AGENCY NAME AND ADDRESS
ATMOSPHERIC SCIENCES RESEARCH LABORATORY - RTP, NC
13. TYPE OF REPORT AND.'ERIOD COVERED
OFFICE OF RESEARCH AND DEVELOPMENT 14. SPONSORING AGENCY CODE
U.S ENVIRONMENTAL PROTECTION AGENCY EPA/600/09
RESEARCH TRIANGLE PARK, NC	 27711
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Observations are presented which substantiate the hypothesis that significant
vertical exchange of ozone and aerosols (and possibly other compounts) occurs
between the mixed layer and the free troposphere during cumulus cloud convect;ve
activity.	 The experiments conducted in July 1981, utilized the airborne UV-DIAL
(Ultra-Violet Differential Absorption Lidar)	 system developed by NASA.	 This system
provides simultaneous range resolved ozone concentration and aerosol back spatter
profiles v;th high spatial	 resolution.	 Data were obtained during the afternoon
along 80 mi East to West and South to North intersecting transects over North
Carolina when cumulus clouds were most active, although nonuniformly distributed.
Evening transects were obtained in the downwind area where the air mass had been
advected.	 Space-height analyses for the evening flight show the cloud "debris" as
patterns of ozone typically in excess of the ambient free tropospheric background.
This ozone excess was approximately the value of the concentration difference between
the mixed layer and free troposphere determined from independent vertical	 Soundings
made by another aircraft in the afternoon.
17.	 KEY WORDS AND DOCUMENT ANALYSIS
a.	 DESCRIPTORS b.IDENTIFIERS/OPEN ENDED TERMS COSATI Field/Group
1
18. DISTRIBUTION STATEMENT 19. SECURITY CLASS (nhReport) 21. NO. OF 'AGES
UNCLASSIFIED 8
RELEASE TO PUBLIC 20. FCCURITY CLASS (This me) 22. PRICE
UNCLASSIFIED
EPA Form 2220-1 (9.73)
NOTICE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
ii
CUMULUS CLOUD VENTING OF MIXED LAYER OZONE
J.K.S. CHING*
U. S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711 USA
S.T. SHIPLEY and E. V. BROWELL
National Aeronautics and Space Administration
Langley Research Center
Hampton, Virginia 23665 USA
and
D.A. BREWER
Systems and Applied Sciences Corp.
Hampton, Virginia 23666 USA
Summer
Observations are presented which substantiate the hypothesis that signif-
icant vertical exchange of ozone and aerosols (and possibly other com-
pounds) occurs between the mixed layer and the free troposphere during
cumulus cloud convective activity. The experiments conducted in July
1981 utilized the airborne UV-DIAL (Ultra-Violet Differential Absorption
Lidar) system developed by NASA. This system provides simultaneous
range resolved ozone concentration and aerosol backscatter profiles with
high spatial resolution. Data were obtained during the afternoon along
1 30 km east to west and sO,.th to north intersecting transects over North
Carolina when non-uniformly distributed cumulus clouds were most active.
Evening transects were obtained in the downwind region, where the air
mass had been adverted. Space-height analyses for the evening flight
,show the cloud "debris" as patterns of ozone typically in excess of the
ambient free tropospheric background. This ozone excess was approx:.-
mately the value of the concentration difference between the mixed
layer and free troposphere determined by DIAL and independent vertical
soundings made by another aircraft in the afternoon.
1.1 Introduction
This paper provides evidence that photochemical oxidants (and other
poll»tants) are transported and deposited above the mixed layer by nonpre-
cipitating cumulus convective cloud processes. Conceptually, during
periods of stro-g solar inso'ation, vigorous rising, thermals produce
cumulus convective clouds which carry mixed layer air in their updrafts.
Some of these clouds can penetrbte the inversion at the top of the mixed
_aver said rise into the free troposphere. These clouds are character-
istically short lived, and as they dissipate, mixed layer pollutants are
deposited aloft. The net pollutant exchange will depend both on the
strength and the areal extent of convective clouds as well as on the
*On assignment from the National Oceanic and Atmospheric Administration,
U. S. Department of Commerce.
4
pollutant concentration differences between the mixed layer and the over-
lying flee troposphere. The US EPA is currently developing a regional
scale pnotochemical oxidant model (6) which addresses the linkage and
exchange that occurs between the mixed layer and the overlying free tropo-
sphere by cumulus convective processes. Recent studies (1, 3, 4, and 5)
provide supporting evidence that this process of 11oud venting occurs, and
these studies are useful in developing the parametric framework for models.
However, there is as yet insufficient observational data to prove that net
vertical transport actually occurs from the mixed layer into the free tropo-
sphere by cumulus cloud venting. Since cloud activity is highly variable
in time and space, an experimental sampling strategy requires highly de-
tailed spatial. and temporal resolution of the pollutant fields. Detailed
space-height cross sections of ozone (and ether pollutants) would provide
a suitable analytical base. These measurements are now obtainable from
airborne UV-DIAL systems capable of remote and range resolved observations
of ozone, aerosols, and other grace gases (2).
The UV-DIAL is a UV differential absorption lidar (DIAL) system
consisting of two frequency-doublet. Nd:YAG lasers which optically pump
two high conversion efficiency tunable dye lasers. The dye lasers are
frequency-doubled into the UV. DIAL measurements of ozone are made in
the Hartley absorption band with the on-line Wavelength nominally set
near 286 nm and the off-line wavelength set near 300 nm. The back-
scattered return signals at these wavelengths are collected by a telescope,
detected by photomultiplier tubes, digitized, and stored on magnetic
tape. The logarithmic difference between the two backscattered signals
is directly proportional to ozone concentration. The UV-DIAL data
acquisition system provides real-time calculations of ozone concentra-
tion profiles. A more detailed description of the UV-DIAL system is
contained in (2).
NASA has successfully developed, demonstrated and deployed the UV-
DIAL system on board ar.. Electra aircraft in a number of field studies (2,8).
Data for this cloud study was sampled at the rate of 5 profiles/second with
a vertical resolution of 15 a. for aerosol and 210 m for ozone. Maximum
horizontal resolution at a nominal ground speed of 100 m/sec is 20 meters.
Confidence in the measurement of ozone concentration is increased by
horizontal averaging. The preliminary analysis presented here uses a 25
shot hor i zontal average corresponding to a horizontal resolution of 50.0 m.
1.2 Description of the Experiment
This experiment follows and characterizes the pollutant distribution
in an air mass known to have experienced active and penetrative cumulus
clouds. Pollutants observed to be imbedded in the layer above the top of
the mixed layer can then be assumed to be remnants of the dissipated
clouds. Such an experiment was conducted by NASA Langley Research Center
using the airborne UV-DIAL on board an Electra. On July 22, 1981, the
Electra flex: two missions over North Carolina, USA. The first mission
pattern consisted of along-wind (east to west) and cross-wind (south to
ncrth) transects centered over Raleigh/Durham (35 052'N, 78047'W) between
1 1500 and 1600 LDT. Each leg was about 130 km long. The evening mission was
located over an area near the Carolina coast which was the projected trajec-
tory of the air mass sampled during the afternoon. The air mass tral4ectory
was subsequently verified by an isentropic analysis. Concurrently, an
instrumented Cessna 402 twin engine aircraft provided correlative vertical
profiles of ozone (0 3 ), Escat (^), temperature (T) and dew point (Td;
2
s -	 ^
derived from sequential down and up ramp patterns along the same flight co-
ordinates. The Electra cruised at 4 km MSL, and provided lidar data from
the surface to 3 km MSL. The Cessna profiles varied from near surface to
greater than 3 km MSL. Satellite data and routine NWS/NOAA surface and
upper air weather observations were archived for subsequent data analysAs.
1.3 Results and Discussion
The mixed layer winds over central North Carolina were generally
north-northwesterly, becoming more westerly with altitude. Above the
mixed layer, the west-northwest flow backed with height to a westerly
flow at 3000 m AGL (Above Grouud Level). The wind speed shear was 2.5
m/sec/km. Nonprecipitating penetrative cumulus clouds were active over the
sampling area from 1400 to 1700 LDT. Cumulus tops varied from 1.5 km to
4 km AGL. The afternoon soundings of T, Td , 03 and 6 obtained by the Cessna
aircraft suggest a mixed layer height of 1600 m. The lapse rate in the
mixed layer was adiabatic up to the base of the elevated inversion at 1600 m,
and the thermal stratification was stable above. Dew point decreased only
slightly within the mixed layer but decreased markedly with altitude above
1600 m. Nephelometer readings indicate some variability in Bscat with alti-
tude and horizontal posit 4 on. Highest values appear to be associated with
the Raleigh-Durham urban plume. However, the Bscat values also exhibit
sharp decreases with altitude above 1600 m. The ozone profiles show mean
mixed layer ozone of about 80 ppbv, but significant horizontal variations
were observed ranging from 75 to greater than 120 ppbv. 	 he latter value
appears to be associated with the Raleigh-Durham urban plume. Above the
mixed layer, a mean but highly variable ozone concentration of about 70
ppbv was observed; ozone concentrations which correspond to mixed layer
values of 80 ppbv were observed when the soundings were taken in the
vicinity of the active cloud areas. The evening soundings indicate a
lower inversion height suggesting subsidence aloft, and are consistent
with a downward motion of approximately 1 cm/sec obtained in the isentropic
flow calculation and kinematic calculation from the NWS soundings (7).
Figure 1 displays UV-DIAL observations of aerosol and ozone cross
sections. In the top panel (Figure 1a), the lidar backscatter cross
section is shown for the south to north transact s tarting at 1538 LDT and
crossing over the Raleigh-Durham airport. Active cumulus clouds attenuate
the return signals and appear as white vertical columns. The mixed layer
is clearly evident where cumulus convection is relatively inactive, as seen
in the southern section at 1540 LDT. The haze is concentrated within the
mixed layer, while lighter shading at higher a p titudes indicates low aero-
sol concentrations aloft. On the other hand, the middle and northern seg-
ments of the flight contain actiive cloud convection. The backscatter dis-
play suggests a higher mixed layer from 1542 to 1554 LDT in the vicinity of
cloud activity. These convective elements literally cloud the issue of
defining a mixed layer depth.
The next panel (Figure lb) depicts the along-wind cross section of
aerosol backscatter on the evening flight mission. With the exception of
a few isola*'ed clouds, the field of cumulus convection is replaced by lay-
ers and patches of aerosol. These layers tilt upward in the vertical from
west to east with an average slope of 16 m/km due to wind speed shear.
Stronger winds at higher altitudes advect the upper portion of the cloud
remnant a greater downwind distance relative to the lower part. Due to a
small but non-negligible shear in wind direction, the flight leg only
intersects a portion of the tilted cloud remnant.
3
Figure 1c shows the along-wind ozone concentration cross section
measured concurrent with the aerosol display of Figure 1b. The ozone data
extends vertically from 1300 to 2500 m MSL. Contour intervals are 10 ppb,
and much of the fin? detail seen in the aerosol gray scale displays has
been smoothed by horizontal and vertical averaging. Ozone concentrations
in excess of 70 ppbv are observed to be distributed in layers coincident
with the aerosol layers of Figure 1b. with identical tilting due to wind
shear. These simultaneous ozone and aerosol scattering measurements are
highly correlated in space. These positive ozone concentration anomalies
are comparable to the average ozone conc:sntrations observed in the after-
noon mired layer.
It should be emphasized that these vented products are not the result
of isolated cumulus events, but represent the integration of many convective
intrusions with subsequent injections of aerosol and ozone into the free
troposphere throughout the afternoon. From this study it is apparent that
intrusive nonprecipitating clouds do deposit mixed layer oxidants and other
pollutants above the mixed layer. These injected pollutants exhibit small
spatial structure and can now be readily investigated by airborne DIAL
systems.
REFERENCES
1. ALKEWEENY, A. and HALES, J.M. (1981). The impact of nonprecipitpting
clouds on the transport and formation of acid aerosols. Annual Meeting
of the American Chemical Society, New York, New York, USA.
2. BROWELL, E.V., CARTER, A.F., SHIPLEY, S.T., ALLEN, R.J., BUTLER, C.F.,
SIVITER, J.H.,JR., MAYO, M.N. and HALL, W.M. (1983). NASA multipurpose
airborne DIAL system and measurements of ozone and aerosol profiles.
Allied Optics, Vol. 22(4), pp. 522-534.
3. CHING, J.K.S. (1982). The role of convective clouds in venting ozone
from the mixed layer. Third Joint Conference on Applications of Air
Pollution Meteorology, San Antonio, Texas. Preprint, American
Meteorological Society, Boston, Massachusctts.
4. CHING, J.K.S., CLARKE, J.F., IRWIN, J.S. and GODOWITCH, J.M. (1983).
Relevance of mixed layer scaling for daytime dispersion based on RAPS
and other field programs. Atmospheric Environment, Vol. 17(4), pp.
854-871.
5. GREENHUT, G.K., CHING, J.K.S., PEARSON, R., JR. and REPOIF, T. (1984).
Transport of ozone by turbulence and clouds in an urban boundary layer.
Journal of Geo h sical Research, Vol. 89 (D3), pp. 4757-4766.
6. LAMB, R.J. 1982. A regional scale (1000 km) model of photochemical
air pollution - Part 1: Theoretical formulation. U.S. Environmental
Protection Agency Report No> EPA-600/3-83-035, U.S. Environmental
Protection Agency, Research Triangle Park, North Carolina, 239 pp.
7. RITTER, J.A. (1983). The vertical redistribution ol" a pollutant
tracer due to cumulus convection. Ph.D. Dissertation, University of
Michigan, Ann Arbor, Michigan, 156 pp.
8. SHIPLEY, S.T., BROWELL, E.V., MCDOUGAL, D.S., ORNDORFF, B.L. and
HAAGENSON, P. (1984). Airborne lidar observations of long-range
transport in the free troposphere. Envir— 	tal Science and
Technology,
	
n1. !R( q )	 "...
Notes: This is an exteided abstract of a presentation and does not
necessarily reflect EPA policy. D. A. Brewer acknowledges support for this
research from NASA Contract No. NAS1-16456.
4
aa
r • uw	 +e+.oc .
!^
€ 2
i
c
a.
0
z	 e o
	 p —
^
a.
0
1
J
'~	 J
I
Figure 1.- Airbor„e lidar observations of aerosol backscattering and ozone
concentrations in the same air mass on July 22, 1981 over North Carolina.
(a) Cross-wind afternoon cross section of aerosol backscatter; (b) along-
wind evening cross section of aerosol backscatter; and (c) along-wind
evening ozone concentration cross section measured simultaneous with (b).
5


Cumulus cloud venting of mixed layer ozone

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server