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Christine L. Haman, Barry Lefer, and Gary A. Morris


Boundary layer height is estimated during a 21-month period in Houston, Texas, using continuous ceilometer observations and the minimum-gradient method. A comparison with over 60 radiosondes indicates overall agreement between ceilometer- and radiosonde-estimated PBL and residual layer heights. Additionally, the ceilometer-estimated PBL heights agree well with 31 vertical profiles of ozone. Difficulty detecting the PBL height occurs immediately following a frontal system with precipitation, during periods with high wind speeds, and in the early evening when convection is weakening, a new stable surface layer is forming, and the lofted aerosols detected by the lidar do not represent the PBL. Long-term diurnal observations of the PBL height indicate nocturnal PBL heights range from approximately 100 to 300 m throughout the year, while the convective PBL displays more seasonal and daily variability typically ranging from 1100 m in the winter to 2000 m in the summer.

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Gary A. Morris, Walter D. Komhyr, Jun Hirokawa, James Flynn, Barry Lefer, Nicholay Krotkov, and Fong Ngan


This paper reports on the development of a new technique for inexpensive measurements of SO2 profiles using a modified dual-ozonesonde instrument payload. The presence of SO2 interferes with the standard electrochemical cell (ECC) ozonesonde measurement, resulting in −1 molecule of O3 reported for each molecule of SO2 present (provided [O3] > [SO2]). In laboratory tests, an SO2 filter made with CrO3 placed on the inlet side of the sonde removes nearly 100% of the SO2 present for concentrations up to 60 ppbv and remained effective after exposure to 2.8 × 1016 molecules of SO2 [equivalent to a column ∼150 DU (1 DU = 2.69 × 1020 molecules m−2)]. Flying two ECC instruments on the same payload with one filtered and the other unfiltered yields SO2 profiles, inferred by subtraction. Laboratory tests and field experience suggest an SO2 detection limit of ∼3 pbb with profiles valid from the surface to the ozonopause [i.e., ∼(8–10 km)]. Two example profiles demonstrate the success of this technique for both volcanic and industrial plumes.

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Vanessa Caicedo, Ruben Delgado, Ricardo Sakai, Travis Knepp, David Williams, Kevin Cavender, Barry Lefer, and James Szykman


A unique automated planetary boundary layer (PBL) retrieval algorithm is proposed as a common cross-platform method for use with commercially available ceilometers for implementation under the redesigned U.S. Environmental Protection Agency Photochemical Assessment Monitoring Stations program. This algorithm addresses instrument signal quality and screens for precipitation and cloud layers before the implementation of the retrieval method using the Haar wavelet covariance transform. Layer attribution for the PBL height is supported with the use of continuation and time-tracking parameters, and uncertainties are calculated for individual PBL height retrievals. Commercial ceilometer retrievals are tested against radiosonde PBL height and cloud-base height during morning and late-afternoon transition times, critical to air quality model prediction and when retrieval algorithms struggle to identify PBL heights. A total of 58 radiosonde profiles were used, and retrievals for nocturnal stable layers, residual layers, and mixing layers were assessed. Overall good agreement was found for all comparisons, with one system showing limitations for the cases of nighttime surface stable layers and daytime mixing layer. It is recommended that nighttime shallow stable-layer retrievals be performed with a recommended minimum height or with additional verification. Retrievals of residual-layer heights and mixing-layer comparisons revealed overall good correlations with radiosonde heights (square of correlation coefficients r 2 ranging from 0.89 to 0.96, and bias ranging from approximately −131 to +63 m for the residual layer and r 2 from 0.88 to 0.97 and bias from −119 to +101 m for the mixing layer).

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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


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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