| Energy structure in China,rich coal resources and lack of oil and gas,made the dominant position of coal.PM2.5 emitted from residential coal combustion has been a major problem to the environmental atmosphere quality.In this work we use a common domestic stove and commercial honeycomb briquette to simulate residential coal combustion resource,monitor and calculate the emission factor of the directly emitted pollutants NOx and PM2.5,which is 0.17 kg/ton coal and 3×10-3 kg/ton coal respectively.According to the investigation data of the application amount of residential briquette,in the simulated full combustion condition in this paper,the NOx and PM2.5 emitted directly from residential coal combustion in Beijing-Tianjin-Hebei region in the heating season were about 243.29 t and 4.29 t respectively.Then we design and manufacture two small outdoor photochemical smog chambers and investigate the secondary particulate matters formation.The two chamber are parallel placement,one is accessed the ambient air as the background chamber,the other is introduced the smoke emitted from the simulated pollution source as the experimental case.The experiment are carried out under the real nature Meteorological parameters,including the temperature,humidity,pressure,and the most important,solar and UV radiation.The characters of the chambers are characterized first,including the light shielding properties,air tightness,mixing and wall effect of the pollutants inside the chamber.The results showed that the condition of shading can completely avoid the influence of environmental ultraviolet radiation,and ensure the stability of the initial state of the experiment;effective mixing time of smog chamber <3 min,half-life of NO2 in the experimental chamber and the background chamber were 231 h and 173.25 h respectively;the half-life of O3 are 51.31 h and 46.20 h,the experimental system could meet the needs of the simulated secondary particle formation experiment.The results of the simulated secondary particle formation experiment showed that the obvious atmospheric photochemical processes can be observed even in the northern regions in winter when the solar ultraviolet radiation was weak.In the experiments,the maximum secondary particle formation rate reached 0.02 ?g/?m3·s?;the initial NOx/VOCs obviously effected the photochemical behavior of the primary pollutants: when the reaction was controlled by NOx,the increase of NOx significantly promoted the photochemical reaction,and a large number of secondary particle formation and the growth of particle size were observed;when the reaction was controlled by VOCs,the excess of NOx significantly inhibited the formation of secondary pollutants?secondary particle and ozone?.Analyzed the particles in different experiments,the results showed,the ratios of organic carbon?OC?and element carbon?EC?in the experimental chamber were greater than two,continuously increased during the reaction period,indicated that the occurrence of atmospheric photochemical processes and the formation of secondary particles;the proportion of phthalic acid which indicates the aging of aerosol increased with the experiment process.This results showed that the secondary particles which generated through photochemical reactions of volatile organic compounds?VOCs?in the experimental chamber have aged;in the scanning electron microscopy?SEM?analysis of particles,the particle sizes continued to grow,containing elements were also constantly enriched,the mass fraction of carbon element increased with the increasing containing element species,which manifested that secondary organic aerosols generated continuously in the experiment process.Finally,based on the average formation rate of secondary particles obtained in this paper,the environmental impact of secondary particles produced by atmospheric photooxidation in Beijing-Tianjin-Hebei region was estimated.The maximum formation rate of the secondary particles was about 0.02 ?g/?m3·s?,and the contribution rate of the secondary particles in the ambient air from residential coal combustion was about 4×10-3 kg/ton coal,the mass of secondary particles produced by residential coal combustion in Beijing-Tianjin-Hebei area was about 5.72 ton,which is more than the primary particle calculated in this paper.It can be concluded that the contribution rate of residential coal combustion to the regional ambient air PM2.5 pollution may be seriously underestimated,and the combined effects of the primary and secondary particles should be considered comprehensively. |
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