Study On Simultaneous Measurement Of Gas And Particle Concentration By Improved Differential Optical Absorption Spectroscopy

In recent years,the decline of air quality and high frequency of haze have obtained the eager concern of public and science researcher,and the monitor of atmosphere environment is highly regarded by government.The measurement of air pollution extensively and long time with high resolution of time and space is important to the research of pollutant formation,pollutant transport,human health and provide data support for various kinds of analysis model.Many countrys establish air quality monitoring station network to monitor the concentration of SO₂,NO₂ and PM（Particulate Matter）.The traditional method of DOAS（Differential Optical Absorption Spectroscopy）can measure the concentration of many kinds of gas such as SO₂ and NO₂,but can’t measure the concentration of PM simultaneously,which limit its application.A novel method called GP-DOAS（Gas&Particle Differential Optical Absorption Spectroscopy）is developed to measure the concentration of SO₂,NO₂ and PM simutanltaneously.As the reality measurement system is non-uniform particle system,there exist many problems such as different kind and diameter of particle and the attenuation cross section will vary with they.These problem increase the difficulty of concentration measurement.A new concept of ESPE（equivalent single particle extinction cross section）is put forward to solve this problem.The ESPE integrate the dimensional distribution function and attenuation cross section.This propose can treat non-uniform particle system as uniform particle,which reduce the difficulty of calculate.After the establish of GP-DOAS and ESPE model,numerical simulation is carried out to verify the method.The error of inversion is very small without noise interference.When the noise of system is big,the error of gas which is weak in differential absorbpiton ability is large.An improvement of moving average filtering is proposed to avoid loss of valid signal.The improvement method reduce the inversion error obviously.Furthermore,the choose of suitable filter window and increase wavelength range can reduce inversion error too.To verify the measurement result,GP-DOAS is used to measure the concentration of SO₂,NO₂ and PM simultaneously at laboratory conditional.Firstly,the experiment of single matter is carried out.For SO₂ from 20 to 200 ppm,the measurement error is lower than 5%mostly.For NO₂ from 100 to 500 ppm,the measurement error is limited in 6%almost.For PM which the diameter is between 400 to 1400 nm,the measurement error is within 10%mainly.Furthermore,simultaneous measurement of gas and particle concentration is carried out.The concentration of SO₂ is varies from 24.5 to 110.3 ppm,while the concentration of NO₂ is varies from 96.1 to 282.6 ppm and the concentration of PM is varies from 3.15×10⁵ to 9.65×10⁵particle/cm³.The measurement error of SO₂,NO₂ and PM is 6%,12%and 11%respectively.The particle emitted by sandalwood combustion at absorption cell is measured,which demonstrate the ability of testing dynamic change by this method.The max value of particle concentration is reached when the oxygen is exhaust at the cell.The particle concentration is declined slowly,and when sweep by N₂,the particle concentration declined quickly.Finally,GP-DOAS is used to measure the gas and particle pollutants at a sewage plant of Hangzhou and Zhejiang University.At sewage plant,the concentration of SO₂is change between 13 and 21μg/m³ and the concentration of NO₂ is between107～205μg/m³.The concentration of NO₂ measured by GP-DOAS is higher than monitoring station nearby,this maybe because of the poor nitrogen removal from municipal sewage due to insufficient carbon source and low C/N value and result in emission in plant.At Zhejiang University,concentration of NO₂ is between 45 and 89μg/m³,and appear two peaks at time of 13:00 and 17:00.The concentration of PM is between 58～143μg/m³,and two peaks appear at 13:00 and 18:00.The tendency of NO₂and PM concentration is agreened,which showed that the urban pollutant maily come from traffic.The results measured by GP-DOAS is agreen with the monitoring station nearby.And the differece maybe because the measurement methods used by monitoring station are point sampling method,which can only represent the measurement points.The results of GP-DOAS represent the average measurement of light path,and can describe situation of big area better.