Chulkyu Lee

Spatial and temporal variations in NO2 distributions over Beijing, China measured by imaging differential optical absorption spectroscopy

During the CAREBEIJING campaign in 2006, imaging differential optical absorption spectroscopy (I-DOAS) measurements were made from 08:00 to 16:00 on September 9 and 10 over Beijing, China. Detailed images of the near-surface NO(2) differential slant column density (DSCD) distribution over Beijing were obtained. Images with less than a 30-min temporal resolution showed both horizontal and vertical variations in NO(2) distributions. For DSCD to mixing ratio conversion, path length along the lines of I-DOAS lines of sight was estimated using the light-extinction coefficient and Angstrom exponent data obtained by a transmissometer and a sunphotometer, respectively. Mixing ratios measured by an in-situ NO(2) analyzer were compared with those estimated by the I-DOAS instrument. The obtained temporal and spatial variations in NO(2) distributions measured by I-DOAS for the two days are interpreted with consideration of the locations of the major NO(x) sources and local wind conditions. I-DOAS measurements have been applied in this study for estimating NO(2) distribution over an urban area with multiple and distributed emission sources. Results are obtained for estimated temporal and spatial NO(2) distributions over the urban atmosphere; demonstrating the capability of the I-DOAS technique. We discuss in this paper the use of I-DOAS measurements to estimate the NO(2) distribution over an urban area with multiple distributed emission sources.

Retrieval of Aerosol Extinction in the Lower Troposphere Based on UV MAX-DOAS Measurements

Multi Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) has been utilized in recent years as a means of deriving vertical profiles of aerosol and trace gases; however, this new technique requires further validation because few studies have investigated its capability. In this study, vertical distributions of aerosol extinction coefficients (AECs) in the lower troposphere were retrieved by applying a recently developed aerosol-retrieval algorithm to O4 slant column densities (SCDs) measured at a UV wavelength (356 nm) using the MAX-DOAS technique. The MAX-DOAS measurements were conducted at the Korea Global Atmosphere Watch Observatory (KGAWO) located off the west coast of Korea during a period of seven cloudless days in May and June 2005. The AECs measured by UV MAX-DOAS varied from 0.05 to 0.73 km−1 in the 0–1 km layer and from 0.01 to 0.20 km−1 in the 1–2 km layer. The AECs for the 1–2 km layer from UV MAX-DOAS are in agreement with lidar data within about 60%. Our results demonstrate the ability of MAX-DOAS as a remote sensing technique for surface aerosol measurements.

Estimation of the rate of increase in nitrogen dioxide concentrations from power plant stacks using an imaging-DOAS

The emission of nitrogen compounds from power plants accounts for a significant proportion of the total emissions of nitrogen to the atmosphere. This study seeks to understand the nature of chemical reactions in the atmosphere involving nitrogen, which is important in undertaking quantitative assessments of the contribution of such reactions to local and regional air pollution. The slant column density (SCD) of power-plant-generated NO2 was derived using imaging differential optical absorption spectroscopy (I-DOAS) with scattered sunlight as a light source. The vertical structure of NO2 SCD from power plant stacks was simultaneously probed using a pushbroom sensor. Measured SCDs were converted to mixing ratios in calculating the rate of NO2 increase at the center of the plume. This study presents quantitative measurements of the rate of NO2 increase in a rising plume. An understanding of the rate of NO2 increase is important because SO2 and NOx compete for the same oxidizing radicals, and the amount of NOx is related to the rates of SO2 oxidation and sulfate formation. This study is the first to directly obtain the rate of NO2 increase in power plant plumes using the I-DOAS technique. NO2 increase rates of 60 and 70 ppb s−1 were observed at distances of about 45 m from the two stacks of the Pyeongtaek Power Plant, northwest South Korea.

MAX-DOAS Measurements of ClO, SO2 and NO2 in the Mid-Latitude Coastal Boundary Layer and a Power Plant Plume

Remote sensing techniques have been preferred for measurements of atmospheric trace gases because they allow direct measurement without pre- and/or post-treatment in the laboratory. UV-visible absorption measurement techniques have been used for ground-based remote sensing of atmospheric trace species. The multi-axis differential optical absorption spectroscopy (MAX-DOAS) technique, one of the remote sensing techniques for air quality measurement, uses scattered sunlight as a light source and measures it at various elevation angles by sequential scanning with a stepper motor. Ground-based MAX-DOAS measurements were carried out to investigate ClO, SO 2 and NO 2 levels in the mid-latitude coastal boundary layer from 27 May to 9 June, 2005, and SO 2 and NO 2 levels in fossil fuel power plant plumes from 10 to 14 January 2004. MAX-DOAS data were analyzed to identify and quantify ClO, SO 2 and NO 2 by utilizing their specifi c structured absorption features in the UV region. Differential slant column densities (dSCDs) for ClO, SO 2 and NO 2 were as high as 7.3 × 10 14 , 2.4 × 10 16 and 6.7 × 10 16 molecules/cm 2 (with mean dSCDs of 2.3 × 10 14 , 8.0 × 10 15 and 1.2 × 10 16 molecules/cm 2 ), respec- tively, at a 3° elevation angle in the coastal boundary layer during the measurement period. Based on the assumption that the trace gases were well mixed in the 1 km height of the boundary layer, estimates of the mean mixing ratios of ClO, SO 2 and NO 2 during the measurement period were 8.4 (±4.3), 296 (±233) and 305 (±284) pptv, respectively. MAX-DOAS measurement of the power plant plumes involved making vertical scans through multiple elevation angles perpendicular to the plume dispersion direction to yield cross-sectional distributions of ClO, SO 2 and NO 2 in the plume in terms of SCDs. Mixing ratios based on the estimated cross-sections of the plumes were 15.5 (ClO), 354 (SO 2 ) and 210 (NO 2 ) ppbv in the plumes of the fossil fuel power plant.

Microphysical properties of low-level clouds and fogs in a mountain area of South Korea

Measurements of microphysical properties in low-level clouds and fogs were carried out at Daegwallyeong in the northeastern mountainous region of South Korea. The microphysical characteristics are presented through analyzing the number concentration, mean diameter, liquid water contents and size distribution of cloud particles sampled with the groundbased Forward Scattering Spectrometer Probe (FSSP). The aim of this study is to analyze the influence of the proposed cloud condensation nuclei (CCN) type on the size and the number of cloud droplets. Observational cases are classified 5 sectors according to backward air mass trajectories from the NOAA/ARL HYSPLIT model. Clean maritime cloud is characterized by sector 1 trajectories and clean continental cloud is by sector 2. Contaminated maritime cloud is by sector 3 and contaminated continental cloud is by sector 4. Sector 5 trajectories are undefined air masses. On average, the droplet number concentrations in marine clouds were lower than for continental c...

Remote Sensing of Tropospheric Trace Gases (NO 2 and SO 2 ) from SCIAMACHY

Atmospheric trace gases can be measured by remote sensing of scattered sunlight from space, using its unique absorption features in the ultraviolet region. The satellite remote sensing approach associated with the spectral fit technique has been successfully employed for measurements of tropospheric trace gases on global and regional scales. Here we present the retrievals of tropospheric traces gases (NO2 and SO2) from SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmsopheric Chartography) onboard the ENVISAT satellite and the calculation of their air mass factor (AMF) used to convert slant columns to vertical columns. The AMF used here is calculated from the integral of the relative vertical distribution of the trace gases from a global 3-D model of tropospheric chemistry (GEOS-Chem), weighted by altitude-dependent scattering weights computed with a radiative transfer model (Linearized Discrete Ordinate Radiative Transfer), and accounts for cloud scattering using cloud fraction and cloud top pressure. The results demonstrate a high sensitivity of the SCIAMACHY instrument to NO2 and SO2 concentrations, and the possibility to retrieve them in the boundary layer.