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James L. McElroy

Abstract

Experimental meteorological tracer data recently collected or declassified concerning dispersion from low-level sources in urban areas are examined in terms of the findings of the St. Louis Dispersion Study. The latter still provides a standard for use in urban air quality models and a basis of comparison for subsequent studies. Collectively, the results indicated that the quantitative findings of the St. Louis project are still valid. However, a tendency for the experimental data to be organized in terms of the local land use, especially nearer the tracer release points, provides evidence that it may be possible to catalog the resulting dispersion parameters in terms of land use and hence decrease the scatter of data points used to develop products such as stability related dispersion curves.

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James L. McElroy

Abstract

A series of low-level tracer experiments conducted in metropolitan St. Louis is described. Values of dispersion parameters, calculated from the tracer data, are related to readily measured or derived meteorological indices of turbulence. The results are presented graphically as families of best-fit curves in terms of downwind distance and travel time. Results are compared with those of previous dispersion experiments conducted over relatively uncomplicated terrain in open country. In terms of the meteorological indices, crosswind dispersion is better described as a function of downwind distance, whereas that in the vertical is about as well described by travel time as by downwind distance. It is concluded that for low-level point sources, the urban area affects crosswind dispersion primarily by enhancing the initial size (i.e., close to the source) of the plume. As the plume becomes much larger than the size of eddies created by the local obstructions, the dispersion closely converges to that associated with flow over open country. In the vertical, significantly enhanced dispersion as well as an enlarged initial cloud dimension occur; the enhancement in the rate of dispersion over that in open country appears somewhat greater for stable than unstable meteorological conditions.

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James L. McElroy
and
Ted B. Smith

Abstract

Airborne lidar and supplementary measurements made during a major study of air chemistry in southern California (SCCCAMP 1985) provided a rare opportunity to examine atmospheric boundary-layer structure in a coastal area with complex terrain. This structure results from a combination of daytime heating or convection in the boundary layer (CBL), the intrusion of a marine layer into the inland areas, the thermal internal boundary layer (TIBL) formed within the marine onshore flow, inland growth of the TIBL, interactions of the CBL and the TIBL, and airflow interactions with terrain features.

Measurements showed offshore mixing-layer thicknesses during SCCCAMP to be quite uniform spatially and day to day at 100–200 m. Movement of this layer onshore occurred readily with terrain that sloped gradually upward (e.g., to 300 m MSL at 50 km inland), but was effectively blocked by a 400–500 m high coastal ridge. In the higher terrain beyond the coastal ridge, aerosol layers aloft were often created as a result of deep convection and of a combination of onshore flow and heated, upslope airflow activity. Such aerosol layers can extend far offshore when embedded in reverse circulations aloft.

The forward boundary of the marine layer was quite sharp, resembling a miniature cold front. Within the marine layer the onshore flow initiates a TIBL at the coastline, which increases in depth with distance inland due to roughness and convective influences. A coherent marine layer with imbedded TIBL was maintained for inland distances of 20–50 km, depending on terrain. Intense heating occurred inland prior to the arrival and undercutting by the marine front. The resulting, effective mixing layer increased in thickness from a few hundred meters to nearly two kilometers in a very short distance.

Comparisons of a representative, physically based TIBL and convective mixing-layer models with observed data indicate that they generally do a credible job of estimating the depth of the marine layer and the CBL when applied appropriately as a function of geographical location and physical situation. Empirical TIBL models usually did not perform as well as physically based models.

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Roger M. Wakimoto
and
James L. McElroy

Abstract

Elevated pollution layers are observed over Los Angeles with an aircraft equipped with a downward-looking lidar. For the first time, detailed ancillary upper-air kinematic and thermodynamic data were collected simultaneously to aid in the interpretation of these elevated layers. It is concluded that upper-level winds within the inversion, orographic effects, and thermally induced changes in the depth of the mixed layer control the evolution of these layers.

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Jhoon Kim
,
Ukkyo Jeong
,
Myoung-Hwan Ahn
,
Jae H. Kim
,
Rokjin J. Park
,
Hanlim Lee
,
Chul Han Song
,
Yong-Sang Choi
,
Kwon-Ho Lee
,
Jung-Moon Yoo
,
Myeong-Jae Jeong
,
Seon Ki Park
,
Kwang-Mog Lee
,
Chang-Keun Song
,
Sang-Woo Kim
,
Young Joon Kim
,
Si-Wan Kim
,
Mijin Kim
,
Sujung Go
,
Xiong Liu
,
Kelly Chance
,
Christopher Chan Miller
,
Jay Al-Saadi
,
Ben Veihelmann
,
Pawan K. Bhartia
,
Omar Torres
,
Gonzalo González Abad
,
David P. Haffner
,
Dai Ho Ko
,
Seung Hoon Lee
,
Jung-Hun Woo
,
Heesung Chong
,
Sang Seo Park
,
Dennis Nicks
,
Won Jun Choi
,
Kyung-Jung Moon
,
Ara Cho
,
Jongmin Yoon
,
Sang-kyun Kim
,
Hyunkee Hong
,
Kyunghwa Lee
,
Hana Lee
,
Seoyoung Lee
,
Myungje Choi
,
Pepijn Veefkind
,
Pieternel F. Levelt
,
David P. Edwards
,
Mina Kang
,
Mijin Eo
,
Juseon Bak
,
Kanghyun Baek
,
Hyeong-Ahn Kwon
,
Jiwon Yang
,
Junsung Park
,
Kyung Man Han
,
Bo-Ram Kim
,
Hee-Woo Shin
,
Haklim Choi
,
Ebony Lee
,
Jihyo Chong
,
Yesol Cha
,
Ja-Ho Koo
,
Hitoshi Irie
,
Sachiko Hayashida
,
Yasko Kasai
,
Yugo Kanaya
,
Cheng Liu
,
Jintai Lin
,
James H. Crawford
,
Gregory R. Carmichael
,
Michael J. Newchurch
,
Barry L. Lefer
,
Jay R. Herman
,
Robert J. Swap
,
Alexis K. H. Lau
,
Thomas P. Kurosu
,
Glen Jaross
,
Berit Ahlers
,
Marcel Dobber
,
C. Thomas McElroy
, and
Yunsoo Choi

Abstract

The Geostationary Environment Monitoring Spectrometer (GEMS) is scheduled for launch in February 2020 to monitor air quality (AQ) at an unprecedented spatial and temporal resolution from a geostationary Earth orbit (GEO) for the first time. With the development of UV–visible spectrometers at sub-nm spectral resolution and sophisticated retrieval algorithms, estimates of the column amounts of atmospheric pollutants (O3, NO2, SO2, HCHO, CHOCHO, and aerosols) can be obtained. To date, all the UV–visible satellite missions monitoring air quality have been in low Earth orbit (LEO), allowing one to two observations per day. With UV–visible instruments on GEO platforms, the diurnal variations of these pollutants can now be determined. Details of the GEMS mission are presented, including instrumentation, scientific algorithms, predicted performance, and applications for air quality forecasts through data assimilation. GEMS will be on board the Geostationary Korea Multi-Purpose Satellite 2 (GEO-KOMPSAT-2) satellite series, which also hosts the Advanced Meteorological Imager (AMI) and Geostationary Ocean Color Imager 2 (GOCI-2). These three instruments will provide synergistic science products to better understand air quality, meteorology, the long-range transport of air pollutants, emission source distributions, and chemical processes. Faster sampling rates at higher spatial resolution will increase the probability of finding cloud-free pixels, leading to more observations of aerosols and trace gases than is possible from LEO. GEMS will be joined by NASA’s Tropospheric Emissions: Monitoring of Pollution (TEMPO) and ESA’s Sentinel-4 to form a GEO AQ satellite constellation in early 2020s, coordinated by the Committee on Earth Observation Satellites (CEOS).

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