Research Of High Sensitivity NO₂ Electrochemical Sensing System For Urban Atmosphere Measurement

As an important atmospheric trace gas,NO₂ is the chief precursor for the generation of photochemical pollution such as ozone and secondary aerosol.It influences the formation of acid rain,photochemical smog and fog,which has become the major obstacle to urban economic development and people's health."13th Five-Year"environmental project clearly pointed out that the total amount of NO_X?NO_X:NO,NO₂?emissions should be reduced by 15%by 2020.Therefore,monitoring the concentration of NO₂ is of vital guiding significance to the assessment of urban air pollution and the formulation of control policy.Traditional optical detection equipment are costly and huge,and monitoring sites are fixed,which fail to adapt to the complex environment.In consideration of these defects,the detection of atmospheric NO₂ by low cost electrochemical sensing technology is carried out in this dissertation.Portable and high sensitivity NO₂electrochemical sensing system for urban atmospheric measurement has been developed.Four-electrode electrochemical sensor was acted as NO₂ concentration sensing carrier,low noise conditioning circuit was acted as the signal conversion carrier,and the interference of zero current drift at trace concentration was compensated based on differential algorithm.Comprehensive processing of data was based on TMS320F28335DSP and long distance anti-jamming data transmission was accomplished by LoRa wireless module.Concentration inversion,correction,display and storage was realized by Lab VIEW monitoring center.Low cost electrochemical sensing for quantification of NO₂ concentration was actualized.Experimental results show that NO₂ can be measured steadily by detecting system based on wireless data transmission,the response time to 100ppbv NO₂ calibration gas is<34s,the sensitivity of the system is 0.242mV/ppbv and the limit of detection is 1.5ppbv?3??for NO₂ at 10s time resolution.To verify the accuracy,experiment system was placed in the northwestern suburb of Hefei for 2 consecutive days of atmospheric NO₂measurements,which was compared with the reference equipment CRDS.The NO₂evolution mechanism is discussed.The data sets for NO₂ exhibit good agreement?R²=0.940?within the combined accuracy of the two methods,except singular part of experiment system as a result of that ambient humidity was close to extreme humidity.Linear fits show a slope of 1.047±0.006,and the reliability of the detection limit is confirmed,the interference sources such as temperature,humidity and other trace gases?O3,NO,SO2?are analyzed in succession.Experimental results show that electrochemical sensing technology provides a low cost,portable and productive measure for the high resolution detection of urban NO₂.It is helpful to generalizing the regional NO₂ distribution characteristics and spatio-temporal evolution rule combined with WSN.It can also provide technological support for NO₂ pollution forecast and warning,governance control and formulation of policy standards.