Effect Of Lightning Activities On Surface Atmospheric Nitrogen Dioxides, Ozone And Particles

Lightning is a commonly-experieced geophysical phenomen.There are 30¹00 lightning discharges per second worldwide.As one of the most common weather disasters,lightning is a direct threat to human life and property safety.Meanwhile,high temperature and high pressure of lightning channel can cause a variety of atmospheric chemical reactions and further affect the atmospheric chemical composition,the air quality and even the climate.Lightning is a major natural source of nitrogen oxides?NO_x?in the atmosphere,and lightning can also affect the abundance of ozone?O₃?in a direct or indirect way,which in turn affects the oxidizing capacity of the atmosphere.Apart from gaseous air pollutants,lightning can result in the generation of new particles in the atmosphere as well.However,an integrated study on lightning activities,meteorological conditions and corresponding variations of surface NO_x,O₃ and particles in relation to thunderstorm has not been studied in China.This study has mainly explored the the temporal and spatial distribution characteristics of cloud-to-ground?CG?lightning activity in Hong Kong and the effect of lightning activities on surface atmospheric NO_x,O₃ and particles,utilizing lightning data from lightning location system,air quality monitoring data,meteorological data and terrain data in Hong Kong,together with the results of artificially triggered lightning experiments carried out in Conghua,Guangzhou.Results of this study have guiding significance in thunderstorm warning,lightning protection and disaster reduction and the evaluation of air quality during thunderstorm seasons.In addition,this study has also provided a new research method and preliminary data for the deeper study on lightning related atmospheric chemistry and related influence mechanisms.Main research topics and results are presented as follows:?1?Temporal and spatial distribution characteristics of CG lightning activity in Hong Kong and related impact factors: CG lightning location data during 2006²012 along with other relevant data,including meteorological parameters and terrain elevation,have been analyzed.Results show that the largest number of CG lightning strokes was detected in 2010 and the smallest number was detected in 2011.As for the monthly variation,the occurrence of CG lightning mainly concentrated between April and September.The most active time for both positive and negative CG lightning strokes was about 1:00 a.m.Meteorological and climate conditions and differences in the thermodynamic characteristics between land and ocean were the main factors that affected the temporal variation of lightning activities in Hong Kong.In terms of spatial distribution,positive CG lightning stroke density over western areas was obviously higher than that over eastern areas,and areas with high negative CG lightning stroke density were mainly located around mountain areas with high terrain elevation.Both positive and negative CG lightning stroke density showed a positive correlation with terrain elevation.?2?Effect of CG lightning activities and meteorological conditions on surface NO_x and O₃ in Hong Kong: Three study sites representing different land use types?urban station Kwai Chung,new town station Tung Chung and background station Tap Mun?during active lightning seasons were studied by analyzing respective air quality monitoring data along with CG lightning and meteorological data.Principal component analysis/absolute principal component scores?PCA/APCS?method and multiple linear regression?MLR?analysis were employed to examine the influence of thunderstorm related lightning and meteorological parameters on surface NO_x and O₃.Results show that concentrations of NO_x increased 4.1%²0.5% and concentrations of O₃ reduced 26.5%⁴4.4% on lightning days at all three study sites in Hong Kong.Results on the influencing factors show that land use type,lightning parameters?e.g.CG lightning stroke frequency and average peak current?and meteorological parameters?e.g.wind direction,wind speed,rainfall,temperature,relative humidity,cloud amount and convective available potential energy?had an important influence on the variation of surface NO_x and O₃ concentrations on lightning days over Hong Kong.?3?Validation of the atmospheric chemical effect of lightning utilizing artificially triggered lightning technology: Concentrations of NO,O₃ and submicron particles have been observed before,during and after five successful artificially triggered lightning experiments on 19 th August,2014.Results of artificially triggered lighting experiments show that average concentration of NO was 0.4 ppbv half an hour before triggering lightning.NO concentration increased rapidly and reached the peak value of 220.5 ppbv after the first successful triggered lightning.NO concentration also increased in different degrees after the other four successful triggered lightning experiments.As for the concentration of O₃,it increased before triggering lightning,but decreased to valley value of 16.9 ppbv after the first successful triggered lightning.Increase of O₃ before triggering lightning might be attributed to the generation of O₃ by the corona discharges in the vicinity of natural lightning flashes nearby and the relatively high-concentration O₃ carried by the downdraft airflow.Decrease of O₃ after successful triggered lightning flashes was due to the titration effect which occurred because freshly emitted NO by lightning reacted rapidly with O₃.In addition,concentration of submicron paticles also increased rapidly after successful triggered lightning experiments.This phenomenon might be related to the new particle formation by ion-induced nucleation during lightning activities.?4?Preliminary study on the the chemical compostion of particles before,during and after artificially triggered lightning utilizing Single Particle Aerosol Mass Spectrometry?SPAMS?: Results from SPAMS show that both average positive and negative ion mass spectra during the process of triggering lightning were similar to those before triggering lightning,and the most significant difference was the appearance of iron ion peaks during the lightning process.Statistical results show that the number of iron-containing particles was significantly higher several minutes after the first successful triggered lightning than other periods.Peak number of iron-containing particles occurred slightly later than the peak value of NO concentration.As iron ions were mainly produced by the melting of rocket wire during the process of triggering lightning,thus the increase of iron-containing particles reflected that the change of chemical components in the lightning channel could also affect the chemical composition of local particles.Besides,statistical results of nitrogen-containing particles show that lightning process could also lead to the increase of nitrate in atmospheric particles.