Ke Dou

Retrieval of ultraviolet skylight radiances and O3 slant column densities from balloon-borne limb spectrometer

With a novel light-weight and absolutely calibrated ultraviolet (UV) spectrometer, UV skylight radiances and O3 slant column densities are measured by balloon-borne limb measurements in Xinjiang area, China. UV skylight radiances measured at the height of 31 km are compared with the results from Modtran in the wavelength range from 290 to 420 nm. O3 slant column densities are derived from radiance spectra in the Huggins bands (320-335 nm) using differential optical absorption spectroscopy method. And the parameter exhibits a good correlation with the same value simulated by radiative transfer model (Tracy). The O3 profile simultaneously measured by an O3 sonde is used as input in Tracy calculations. The O3 sonde is launched on the same balloon.

Measurement of Ammonia by a Portable UV-DOAS Gas Sensor Based on Multi-Pass Cell

Ammonia, the third most important abundant nitrogen compound, is a primary alkaline gas in the atmosphere. It has strong absorption bands in the deep ultraviolet (DUV) spectral range and so can be reliably detected by the differential optical absorption spectroscopy (DOAS) technique. A portable UV-DOAS gas sensor based on multi-pass cell has been designed to detected trace gases, especially for ammonia, in the DUV spectral range, with good performance using a broad-band Deuterium source and high-sensitivity spectrometer. With the optical path as long as 20m, such a sensor could detected NH3 concentrations as low as 100ppb according to the result of in-situ measurement. Fast response time and low measurement error of this portable gas sensor could be competent for emergency monitoring.

Monitoring of SO2 emissions from industry by passive DOAS

Sulfur dioxide is a highly toxic air contaminant that harms human health and damages the environment. It is easily converted to sulfuric acid which is the major component in acid rain and to sulfate particles. Coal-burning power plants are the main sources of SO2 pollution. It is necessary to evaluate the emissions from industry for emission reduction strategies. Passive DOAS method has been successfully applied in volcanic plume and atmosphere monitoring because of its advantage of relative simple system with no light source. Here we report the measurement of SO2 total flux from a chimney in plant area in Hefei city (China) with a compact passive DOAS system. The system consists of a small telescope pointing zenith direction and a fibre-coupled OceanOptics USB2000 spectrometer. In the measurement the system was mounted on a mobile platform moving under the plume approximately perpendicular to the plume transport direction and the spectra of the zenith direction were recorded. By combining the integrated gas concentration over the plume cross section with wind velocity data SO2 flux was estimated.

A new type UV-visible DOAS system based on photodiode array (PDA)

DOAS technique provides a more representative picture of air quality and typical urban exposures over traditional point monitoring equipments it has been widely used for urban air quality monitoring in China. Most commercial DOAS instruments presently used for air quality monitoring adopt photomultiplier and scanning slit as detector which is called slotted disk (SD) detector. In contrast with the SD detector Photodiode Array can overcome the problem of scintillation noise caused by atmospheric turbulence and reduce photon noise. We report here a new type UV-visible DOAS system based on photodiode array. The properties of the system including offset dark current noise linearity of the detector and resolution stray light ofthe spectrometer are described. Field observations of a number of pollutants (e.g. S02, NO2, 03 and HCHO) were performed in the urban area of Beijing City during August 2004. The measurement results show that the system fulfils automatic ambient air monitoring with high time resolution and sufficient sensitivity.