Smog Chamber Studies Of The Photooxidation Of Propane, Isobutane And Isohexane

The photochemical ozone reactivity of propane, isobutane and isohexane were studied by smog chamber in this work. The effects of relative humidity (RH) and the initial ratios of reactant concentration on the photochemical reactivity of these species are mainly investigated. The comparison between smog chamber data and the results from simulation of alkane sub-mechanism of MCMv3.1is also made.In the photochemical reaction system of propane and NOx, the maximum ozone concentration (O3max), the maximum value of incremental reactivity (IRmax) of propane and the occurrence time of peak ozone concentration all decrease with increasing RH. Under the lower RH conditions, the IRmax varies from0.0231to0.0391, while under the higher RH conditions, the IRmax ranges from0.0172to0.0320. During4-20h of experiments, acetone concentrations range from153ppb to364ppbat17%RH and from167ppb to302ppb at62%RH, respectively. O3max decrease with increasing [C3H8]0/[NOx]0ratio and a better linear negative relationship between them is obtained under the lower RH conditions. The comparison between smog chamber data and the results from simulation of the C3Hs-NOx reactions using the sub-mechanism of MCM is also made, and a significant deviation between the two results is found.In the photochemical reaction system of isobutane and NOx, O3max linearly decrease with increasing RH, the occurrence time of peak ozone concentration, IRmax value of isobutane as well as acetone concentration all decrease generally with increasing RH. A linear negative relationship between O3max and [IC4H10]0/[NOx]0ratio is obtained, greater amount of acetone at the4hrs of reaction with lower ratio, whereas opposite trend after8h of reaction is found. Experimental O3max is5%to20%larger than MCM simulated O3max, the occurrence time of peak ozone concentration in the experiment is about5times than MCM simulated results. Experimental yield of acetone product is less than MCM simulated results, the distinct deviation between them would decrease with the evolution of reaction.In the photochemical reaction system of ishexane and NOx, as the HONO is introduced to the system, hydroxyl radical will generate in the beginning of reaction, RH does not affect O3max, the appearance time of O3max and the yield of acetone product much, but O3max has a little reduce trend with increasing RH. The initial concentration of added HONO will affect reaction system especially. When the amount of initial HONO changes from120.5ppb to275ppb,O3max will increase48%, IRmax will increase51%, the average concentration of acetone and propanal will increase54%and34%, respectively. When the amount of initial HONO changes from275ppb to427ppb,O3max and IRmax will be nearly unchanged, the average yield of acetone and propanal will increase9%and7%, respectively.The simulated results from the sub-mechanism MCMv3.1of isohexane agree with the experimental results at the yield of O3and NOx. The yield of acetone product has the same trend between simulated and experimental results, but experimental results are obvious larger than simulated results, and analyzes the reasons for the errors between the simulation results and experiment data.