Development Of Wet-Chemistry Long Path Absorption Spectroscopy For Nitrous Acid (HONO) Detection And Its Application In The Atmosphere

As one of the major sources of OH radical in the atmosphere,HONO plays an important role in the atmospheric enviroument,affecting the oxidative degradation of pollutants in the atmosphere and accelerating the process of air pollution.As a typical urban pollutant,HONO plays an important role in the formation of brownish haze,as well as in atmospheric photochemical processes.It is significant for assessing regional atmospheric oxidation capacity and establishing regional photochemical pollution control strategies.In this context,we have set up an on-line measuring instrument for observing HONO in the atmosphere.Compared with commercial instruments,the home-made HONO analyzer reduced the cost of the instrument,we conducted field observations in winter using the instrument.In this study we analyzed the diurnal variation of HONO,the relationship with the photolysis frequency,and the influence of wind direction and wind speed on HONO.We also explored the nighttime formation of HONO.The preliminary conclusions are as follows:The basic parameters of the instrument(detection limit,time resolution,collection efficiency,delay time,and uncertainty)were determined.The dual-channel calibration results show that the correlations of the two channels are both greater than 0.99.This shows a good linearity and suggests the reliability of the home-made HONO instrument and HONO generation system.Interference experiment results show that only NO2 will generate interference signals to HONO.Through filed measurments and verification tests,the instrument has been demonstrated to be stable for a long period of observation and in good condition.The data also show the reliability of the instrument.The HONO concentration ranged from 0.05 to 7 ppbv,with an average of 1.32±0.92 ppbv.After sunset,the HONO concentration rapidly increased and gradually accumulated during nighttime,reaching a maximum of approximately 1.93 ppbv at 8:00 am.The correlation analysis shows that the heterogeneous transformation of NO2 during nighttime is the main source of HONO,and the direct emission contributes little to HONO.The study found that the average ratio of HONO/NO2 increased with the increase of RH.On average,HONO/NO2 began to increase shortly after sunset,and plateaued at 0.056.The increase in HONO/NO2 is accompanied by an increase of HONO,indicating that NO2 is continuously converted to HONO through a heterogeneous reaction.In addition to the local accumulation of HONO at night during winter,the transmission of pollution from the direction of east,southeast and northeast were also observed.The clean air mainly came from the northwest.There was a significant negative correlation between the wind speed and the HONO concentration,and when the wind speed is in the range of 3.0-4.0 m s-1,there is a certain degree of increase in the concentration of HONO concentration and PM2.5 mass,this indicating that it may be related to the local extraneous HONO and the transmission of pollutants,mainly in the east,southeast,and northeast directions.