Study On Peroxides Concentration And Its Influencing Factors In The Urban Atmosphere

Hydrogen peroxide and organic peroxides are important oxidants in the atmosphere, they are also reservoir of free radicals such as OH and HO2and play important roles in the atmospheric chemistry. Measurement of peroxides can help us understand atmospheric photochemical reaction and formation mechanism of acid rain, and to prevent the air pollution.In this paper we have used the best collection method-the mist chamber with collection solution of pH7H2O to study the sulfur dioxide interference on collection of low concentration of hydrogen peroxide. And the decomposation of organic peroxides on the surface of the glass were also studied. We also test this collection method in the field in order to make the measurement of gas-phase peroxides more accurate. The gas-phase peroxides concentration in the atmosphere has then been measured in Beijing, China.The result of collection method study shows that different concentration of sulfur dioxide has different impact on collecting hydrogen peroxide. For the same concentration of hydrogen peroxide, higher concentration of sulfur dioxide has higher impact on collecting. For the same concentration of sulfur dioxide, lower concentration of hydrogen peroxide suffer higher impaction from sulfur dioxide. Hydroxymethyl hydrogen peroxide(HMHP) can decompose in the surface of glasses if the collection time is longer than30min. Methyl hydrogen peroxide(MHP) will decompose and suffer interfere from SO2during collection. The best collection method is suit for collecting MHP while the concentration of hydrogen peroxide is lower enough to reaction with SO2Thus, we should use the neutral collection solution to collect MHP while the concentration of H2O2is low or SO2is high.The gas-phase peroxides concentration in the atmosphere has been measured in Beijing,China. Result shows that the peroxide detected in the atmosphere were hydrogen peroxide, methyl hydrogen peroxide and hydroxyl methyl hydrogen peroxide. The average concentration is1.25ppbv,0.104ppbv and0.037ppbv. The concentration of hydrogen peroxide and methyl hydrogen peroxide were both high in summer and low in spring and autumn. The diurnal variation were low in the morning and high in the afternoon.The maximum concentration usually appear between12:00to16:00and always rise after18:00. Methyl hydrogen peroxide has no obvious variation in the daytime and the maximum concentration usually appear after17:00. The result of the correlation between peroxides and effect factors shows that hydrogen peroxide has strong positive correlation with ozone and temperature, and has negative correlation with nitric oxide and carbon monoxide. Only when the relative humidity is higher than80%, it has negative correlated with particulate matter and sulfur dioxide. Hydrogen peroxides in Beijing is mainly produced by photochemical process, and the increased concentration at night is influenced by motor vehicle exhaust emission of hydrocarbon.MHP is mainly produced by reaction of hydrocarbon with O3or OH.