Xie Pinhua

Intercomparison of Nox,SO2,O3,and Aromatic Hydrocarbons Measured by a Commercial DOAS System and Traditional Point Monitoring Techniques

A field-based intercomparison study of a commercial Differential Optical Absorption Spectroscopy (DOAS) instrument (OPSIS AB, Sweden) and different point-sample monitoring techniques (PM, based on an air monitoring station, an air monitoring vehicle, and various chemical methods) was conducted in Beijing from October 1999 to January 2000. The mixing ratios of six trace gases including NO, NO2, SO2, O3, benzene, and toluene were monitored continuously during the four months. A good agreement between the DOAS and PM data was found for NO2 and SO2. However, the concentrations of benzene, toluene, and NO obtained by DOAS were significantly lower than those measured by the point monitors. The ozone levels monitored by the DOAS were generally higher than those measured by point monitors. These results may be attributed to a strong vertical gradient of the NO-O3-NO2 system and of the aromatics at the measurement site. Since the exact data evaluation algorithm is not revealed by the manufacturer of the DOAS system, the error in the DOAS analysis can also not be excluded.

Measurements of Nighttime Nitrate Radical Concentrations in the Atmosphere by Long-Path Differential Optical Absorption Spectroscopy

The long-path differential optical absorption spectroscopy (LP-DOAS) technique was developed to measure nighttime atmospheric nitrate radical (NO3) concentrations. An optimized retrieval method, resulting in a small residual structure and low detection limits, was developed to retrieve NO3. The time series of the NO3 concentration were collected from 17 to 24 March, 2006, where a nighttime average value of 15.8 ppt was observed. The interfering factors and errors are also discussed. These results indicate that the DOAS technique provides an essential tool for the quantification of NO3 concentration and in the study of its effects upon nighttime chemistry.

Water Vapor Interference Correction in a Non Dispersive Infrared Multi-Gas Analyzer

We demonstrate an effective method to eliminate the interfering effect of water vapor in a non-dispersive infrared multi-gas analyzer. The response coefficients of water vapor at each filter channel are measured from the humidity of the ambient air. Based on the proposed method, the water vapor interference is corrected with the measured response coefficients. By deducting the absorbance of each filter channel related to water vapor, the measuring precision of the analyzer is improved significantly and the concentration retrieval correlation accuracy of each target gas is more than 99%.

Cross-interference correction and simultaneous multi-gas analysis based on infrared absorption

In this paper, we present simultaneous multiple pollutant gases (CO2, CO, and NO) measurements by using the non-dispersive infrared (NDIR) technique. A cross-correlation correction method is proposed and used to correct the cross-interferences among the target gases. The calculation of calibration curves is based on least-square fittings with third-order polynomials, and the interference functions are approximated by linear curves. The pure absorbance of each gas is obtained by solving three simultaneous equations using the fitted interference functions. Through the interference correction, the signal created at each filter channel only depends on the absorption of the intended gas. Gas mixture samples with different concentrations of CO2, CO, and NO are pumped into the sample cell for analysis. The results show that the measurement error of each gas is less than 4.5%.

Comparing different light-emitting diodes as light sources for long path differential optical absorption spectroscopy NO2 and SO2 measurements

In this paper, we present a comparison of different light-emitting diodes (LEDs) as the light source for long path differential optical absorption spectroscopy (LP-DOAS) atmospheric trace gas measurements. In our study, we use a fiberoptic design, where high power LEDs used as the light source are coupled into the telescope using a Y shape fiber bundle. Two blue and one ultraviolet (UV) LEDs with different emission wavelength ranges are tested for NO2 and SO2 measurements. The detailed description of the instrumental setup, the NO2 and SO2 retrieval procedure, the error analysis, and the preliminary results from the measurements carried out in Science Island, Hefei, Anhui, China are presented. Our first measurement results show that atmospheric NO2 and SO2 have strong temporal variations in that area and that the measurement accuracy is strongly dependent on the visibility conditions. The measured NO2 and SO2 data are compared to the Ozone Monitoring Instrument (OMI) satellite observations. The results show that the OMI NO2 product underestimates the ground level NO2 by 45%, while the OMI SO2 data are highly influenced by clouds and aerosols, which can lead to large biases in the ground level concentrations. During the experiment, the mixing ratios of the atmospheric NO2 and SO2 vary from 8 ppbv to 36 ppbv and from 3 ppbv to 18 ppbv, respectively.

Measurements of NO2 mixing ratios with topographic target light scattering-differential optical absorption spectroscopy system and comparisons to point monitoring technique

A topographic target light scattering-differential optical absorption spectroscopy (ToTaL-DOAS) system is developed for measuring average concentrations along a known optical path and studying surface-near distributions of atmospheric trace gases. The telescope of the ToTaL-DOAS system points to targets which are located at known distances from the measurement device and illuminated by sunlight. Average concentrations with high spatial resolution can be retrieved by receiving sunlight reflected from the targets. A filed measurement of NO2 concentration is performed with the ToTaL-DOAS system in Shijiazhuang in the autumn of 2011. The measurement data are compared with concentrations measured by the point monitoring technique at the same site. The results show that the ToTaL-DOAS system is sensitive to the variation of NO2 concentrations along the optical path.

A Scanning Multi-Axis Differential Optical Absorption Spectroscopy System for Measurement of Tropospheric NO2 in Beijing

A scanning multi-axis differential optical absorption spectroscopy (DOAS) system is developed for monitoring tropospheric NO2 abundance. Measurements at different viewing angles near the horizon can be performed sequentially with one telescope collecting scattered sunlight reflected by a moving mirror. Tropospheric NO2 diurnal variations can be derived from slant column densities (SCDs) of different elevation angles. The result from a field campaign in Beijing in summer of 2005 reveals potential possibility for the monitoring of tropospheric NO2 by multi-axis DOAS technique.

Application of Kalman Filtering and Wavelet Transform in DOAS

Differential optical absorption spectroscopy (DOAS) has become a widely used method to measure trace gases in the atmosphere. Concentration of trace gases is retrieved by fitting reference spectra to the atmospheric absorption spectra. There were large errors in retrieved results, when absorption structures were heavily overlapped and the noises were high. The novel method of combining Wavelet transform and Kalman filtering was developed and applied to DOAS data processing. The experiment results show the method can effectively correct overlapped spectra and reduce the noise. The novel method improves the accuracy of the DOAS system

Stereoscopic monitoring technology andapplications for the atmospheric environment in China

Human activity and natural sources have released a large number of pollutants into the atmospheric environment, which seriously influences the survival conditions of many creatures of the planet. The economy has grown rapidly in recent years; however China is now faced with some of the world’s most severe and complex environmental problems. The promotion of atmospheric and environmental science research is imperative in solving the climate and environmental issues with which human beings are now faced. With obvious temporal and spatial change features, typical geographical conditions and regional climatic characteristics, these factors influence air quality and climatic change. Therefore, interdisciplinary research on optics and the environment is emphasized with the goal of producing comprehensive and stereoscopic monitoring technology for the atmospheric environment. Increased monitoring technology level of the atmospheric environment and the development of remote sensing observation methods, including online, rapid, and stereoscopic detection of atmospheric environmental data, are essential in understanding the dynamic change process and source mechanism of various components in the atmosphere, as well as in understanding their influence on environment and climate. In recent years, newly developed laser/spectrum technology was used to study trace pollutants and atmospheric compositions, including UV/visible/IR spectrum technology, laser spectrum technology, and optical remote sensing technology. Multiple detection technology was formed through absorption, a scattering and emission process caused by mutual interaction between light and substances in the atmosphere. This technology is capable of rapid and real-time detection of atmospheric trace gas, atmospheric aerosol, greenhouse gas, atmospheric wind fields, aqueous vapor, temperature, and atmospheric pollution. More specifically, differential optical absorption spectroscopy (DOAS) is a continuously developing spectroscopy technology, and it is widely used in the detection of atmospheric components. The Chinese Academy of Sciences (CAS) has taken the lead in conducting research using the active DOAS technique, the ground-based passive DOAS technique (multi-axis DOAS and mobile DOAS), and the airborne and space-based DOAS technique in China. A unique MAX-DOAS observation network was established in Eastern China to perform long-term observation of trace gases (e.g., NO2, SO2, etc.) and aerosol in the troposphere (since 2008 for the majority of the sites, and since 2012 for other sites). This observation research provides an effective optical remote sensing technique for the measurement of distributions and emissions from point and area sources and high-tech support for emission control of pollutants. Light detection and ranging (LIDAR) remote sensing techniques, both ground-based and airborne, were developed for measuring of atmospheric components. These established, advanced LIDAR systems, most of which were first built in China, were used for measuring the vertical profiles of atmospheric aerosol, temperature, water vapor, pollution, and gases (e.g. NO2, SO2, O3, etc.) in the boundary layer, greenhouse gas (CO2) in the troposphere, temperature and ozone in the stratosphere, and wind with a high vertical resolution. According to the measurement needs of industrial areas (e.g., petrochemical industry zones and large garbage disposal fields) and unexpected spill accidents involving dangerous chemicals, the research and development platform technique of Fourier Transform Infrared Spectrum (FTIR) has been implemented in many field campaigns. The aim of FTIR is to study regional air pollution (including the distribution, transport, and evolution of pollutants and source identification), as well as free atmospheric radicals and photo-chemical intermediates and production. The temporal and spatial distribution of atmospheric composition (e.g., greenhouse gases, pollutant gases, and aerosols) is observed by ground-based troposphere observation networks. These networks also provide remote satellite sensing ground validation.

The multiple scattering expansion coefficients of cluster soot particles

Carbonaceous soot and aerosols found in nature often have cluster structure. In this paper the rigorous analytic interactive scattering fields multiple expansion coefficients of cluster spheres are presented.