High sensitivity simultaneous measurements of atmospheric NO<sub>2</sub> and HONO using incoherent broadband cavityenhanced absorption spectroscopy (IBBCEAS) were developed. A near-ultraviolet light emitting diode (LED) peaked at 372 nm was used as light source of the IBBCEAS instrument to measure the absorption of NO2 and HONO in the spectral range of 361-378 nm. Concentrations of atmospheric NO<sub>2</sub> and HONO were retrieved from the absorption spectra recorded in the absence of atmospheric aerosols and the average detection limits of 2.9 ppbv for NO<sub>2</sub> and 1.2 ppbv for HONO with an acquisition time of 5 min were achieved. The results demonstrated high sensitivity of this measurement technique based on IBBCEAS, which is a promising technique for measurements of atmospheric trace gases.
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.
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. S0<sub>2</sub>, NO<sub>2</sub>, 0<sub>3</sub> 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.
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 SO<sub>2</sub> 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 SO<sub>2</sub> 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 SO<sub>2</sub> flux was estimated.