Somg Chamber Experiments Of Toluene Photochemical Reaction Under Complex Pollution Scenarios

Toluene,isoprene and ethylene are typical volatile organic compounds(VOCs)in the atmosphere that photochemically react with nitrogen oxides(NOx)to form ozone(03)and secondary organic aerosols(SOA)under light conditions,polluting the atmosphere,endangering human health.Based on typical atmospheric pollutants(toluene,isoprene and ethylene)and typical conditions(about 25ppb initial NO2 concentration,5ppb NO initial concentration,temperature of 303?305K and relative humidity of 15%?20%).A photochemical reaction of toluene with NOx and various VOCs under complex pollution was carried out.During the experiment,gas analyzer,SMPS and DMA-APM-CPC were used to detect O3 concentration,SOA particle size distribution and effective density which were dynamically changing with time.Besides,combined with theoretical simulation and experimental study,the photooxidation O3 of toluene,isoprene and ethylene was simulated using the California Air Pollution Research Center Mechanism(SAPRC)model based on the smog chamber experiment,and compared results with the experimental results.O3max refers to the maximum value of O3 generated within 480 min of reaction.The main conclusions are as follows:Formation of O3 and SOA from toluene and NOx reaction system.The initial concentration of toluene ranged from 14.2 ppb to 107 ppb,with the increasing of initial toluene concentration,the O3max increases with the increase of the ratio of toluene/NOx ratio of less than 11.3.The fitting formula is O3max = 5.3+11.6×Toluene/NOx ratio,R2=0.97,When the toluene/NOx ratio is greater than 15.5,O3max is about 120 ppb.The model simulation results are in good agreement with the experimental results,and the simulation results is over-estimate by 16.7%.The decay rate of toluene increased from 5.3%to 58.3%with the increase of toluene/NOx ratio.NO2 concentration decreased rapidly at the beginning of reaction,and then gradually increased,while the concentration of NO was opposite.In addition,the reference value of effective density of SOA in the above system is 1.35g/cm3,and yield(the ratio of SOA mass concentration and VOCs consumption)decreases from 0.38 to 0.19 with the increase of the ratio.Besides,SOA generation is later than O3 generation,and the peak particle size after SOA nucleation rapidly increases.A variety of VOCs and NOx photochemical reaction system.The initial concentration of VOCs is about 15 ppb,mixed at a 1:1 ratio.Compared with single toluene and two VOCs mixture systems,the results showed that the addition of isoprene or ethylene promoted the formation of O3,O3max increased by 203%and 106%,respectively.The nucleation of SOA was inhibited and the nucleation time was delayed by about 50min,SOA yield were decreased.While the isoprene and ethylene added at the same time,the generation of O3max between single and two VOCs mixed systems.After the nucleation,the peak particle size ranged from 14.1nm to 50.9nm,which was narrower than that of single or two VOCs mixed systems.The effect of O3 generation of precursor VOCs.On the basis of smog chamber experiment,using SAPRC to simulate the variation of O3max of toluene,isoprene or ethylene with the corresponding ratio,the theoretical O3 concentration values are estimated on the assumption that the toluene,isoprene and ethylene do not affect each other.The results showed that because of the interaction between toluene and ethylene offset each other,the simulated value of toluene mixed with ethylene was close to the experimental value(??0),so the effect on the formation of O3 was not obvious.In toluene/isoprene,isoprene/ethylene system,the experimental values were greater than the simulation value(?>0),this is due to the fact that the consumption rate in the mixed system is greater than that of a sigle system,which promotes the generation of O3;While the experimental values of the three organic compounds were less than the simulated values(?<0),which maybe the different consumption rate of each VOCs or the high NO concentration,so O3 generation was inhibited.Therefore,the management and control of O3 need to combine the contribution of each VOCs.