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Investigation of the Ozone Formation Potential for Ethanol Using a Smog Chamber

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Investigation of the Ozone Formation Potential for Ethanol Using a Smog Chamber Article Atmospheric Science December 2012 Vol.57 No.34: 44724481 doi: 10.1007/s11434-012-5375-9 Investigation of the ozone formation potential for ethanol using a smog chamber JIA Long, XU YongFu* & SHI YuZhen State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China Received April 13, 2012; accepted May 28, 2012; published online August 7, 2012 The ozone formation reactivity of ethanol has been studied using chamber experiments and model simulations. The computer simulations are based on the MCM v3.1 mechanism with chamber-dependent auxiliary reactions. Results show that the MCM mechanism can well simulate C2H5OH-NOx chamber experiments in our experimental conditions, especially on ozone formation. C2H5OH-NOx irradiations are less sensitive to relative humidity than alkane species under our experimental conditions. In order to well simulate the experiments under high relative humidity conditions, inclusion of N2O5+H2O=2HNO3 in the MCM mechanism is necessary. Under C2H5OH-limited conditions, the C2H5OH/NOx ratio shows a positive effect on d(O3-NO)/dt and RO2+HO2. High C2H5OH/NOx ratios enhance the production of organoperoxide radical and HO2 radical concentrations, which leads to a much quicker accumulation of ozone. By using ozone isopleths under typical scenarios conditions, the actual ozone formation ability of ethanol is predicted to be 2.3–3.5 part per billion (ppb) in normal cities, 3.5–146 ppb in cities where ethanol gas are widely used, and 0.2–3.2 ppb in remote areas. And maximum ozone formation potential from ethanol is predicted to be 4.0–5.8 ppb in normal cities, 5.8–305 ppb in cities using ethanol gas, and 0.2–3.8 ppb in remote areas. ethanol, ozone, photochemical smog, MCM, smog chamber Citation: Jia L, Xu Y F, Shi Y Z. Investigation of the ozone formation potential for ethanol using a smog chamber. Chin Sci Bull, 2012, 57: 44724481, doi: 10.1007/s11434-012-5375-9 Ozone pollution produced by volatile organic compounds Atmospheric ethanol has been measured for more than (VOCs) and nitrogen oxides (NOx, x=1,2) irradiations is a 20 years. It has been found that urban mean concentrations serious environmental problem in large cities all over the of ethanol range from 0.7 to 12 ppb, whereas the cities world. There are many studies to investigate ozone for- where the ethanol gas is widely used exhibit the highest mation potential of different types of VOC spices [1–6]. ethanol mean concentrations from 12.1 to 414 ppb [7]. Both Ethanol (C2H5OH) is widely used as a solvent and a popular anthropogenic and natural sources make the contribution of biofuel alternative to gasoline in the world. China has pro- ethanol concentrations. 4.8 ppb of ethanol was found up- moted ethanol-based fuels on a pilot basis in five cities in its wind a furniture factory and 461 ppb downwind [8]. The central and northeastern regions since 2002 (http://english. role of natural sources is small in the urban areas. It has people.com.cn/200206/17/eng20020617_98009.shtml). The been found that the ethanol concentrations from natural annual output of ethanol fuels was 486 millions of U.S. liquid sources spread from 0.04 to 1.2 ppb in rural and remote gallons in 2007 (http://www.ethanolrfa.org/page/-/objects/ areas. In forested areas the ethanol concentrations due to pdf/outlook/RFA_Outlook_2008.pdf). With the increasing sources from trees and pastures are much higher [7]. common use of ethanol, the ethanol concentrations in the There are still many arguments about ethanol’s pollution atmosphere will probably increase. problems, especially about its ozone pollution problem. Pe- reira et al. [9] used a mixture 22%–24% of anhydrous etha- *Corresponding author (email: [email protected]) nol in gasoline and hydrated ethanol as potential precursors © The Author(s) 2012. This article is published with open access at Springerlink.com csb.scichina.com www.springer.com/scp Jia L, et al. Chin Sci Bull December (2012) Vol.57 No.34 4473 for ozone formation, and found that the ozone peak concen- prepared from pure ethanol (C2H5OH, AR99.7%, Beijing trations are in average 28% higher for alcohol than for the Chemical Factory) in a 2 L bottle and diluted by high-purity mixture. Jacobson [10] studied the effects of ethanol versus N2. The prepared gaseous ethanol mixture was injected into gasoline vehicles on cancer and mortality in the United the reactor using a syringe. Ethanol concentrations in the States, and found that ethanol may make air even dirty and reactor were calculated from the amount of organic com- increase ozone-related mortality. Howard et al. [11] directly pounds introduced into the reactor and the volume of back- measured the ozone formation potential from dairy emis- ground air used in the experiments. It was confirmed that sions using a mobile chamber, and found that the majority the calculated concentrations of ethanol agreed to within of the ozone formation could be mainly explained by etha- better than ±5% with the concentrations quantitatively de- nol in the emissions from the dairy cows, but the ozone tected by the gas chromatograph of GC112A (Shanghai formation potential is generally small. In addition, the Precision Scientific Instrument Co, Ltd). CO, NO and NO2 maximum incremental reactivity (MIR) of 0.43 ppm/ppmC in a purity of 99.9% were from the Beijing ZG Special for ethanol reported by Carter [3] indicates that the ozone Gases Science & Technology Co., Ltd. Low concentration formation potential of ethanol may be important. NO2 (9 ppm) was a gaseous mixture of high-purity N2 (Chi- Nevertheless, the chamber experiments about the reactiv- nese National Research Center for CRM’s). ity of ethanol are still limited. The object of this work is to study the role of ethanol in ozone formation in terms of 1.3 Experimental procedure and conditions chamber experiments. Several C2H5OH-NOx-air irradiations were performed under different conditions. The results are In this study, two sets of experiments were conducted to used to study different factors impacting on the ozone for- investigate O3 formation of ethanol under different relative mation from ethanol. The detailed chemical mechanism of humidity conditions, including the 5% and 50% RH condi- ethanol from the Master Chemical Mechanism (MCM v3.1) tions. Before experiments, the reactor was washed using N2 is used to explain the decay process of ethanol. The experi- (99.9992%), until O3 and NOx concentrations were under mental data are compared with the model simulation. Com- the detecting limit. For low RH condition experiments, after bination of experimental data and simulation results gives synthetic air was introduced into the reactor as background the reactivity of ethanol. The ozone formation potential of gas, the given quantity of ethanol and NOx was sequentially ethanol is further discussed. introduced into the reactor. Then the reactor was vigorously shaken to make the reactants mixed thoroughly. For the experiments under the 53% RH condition, a given quantity 1 Experimental of the pure water was injected into the reactor directly with a syringe, and measured by JinMin RH analyzer when water 1.1 Equipment was completely evaporated. After which the reactor was A smog chamber was designed to investigate the photochem- maintained in the dark for 1 h without any activities. Then istry of volatile organic compounds. The whole facility has the light was switched on for irradiation, and meantime a fan been used to study the reactions of ozone with ethylene [12], was turned on to keep the same temperature in the closure. propylene [13], dimethyl sulfide [14] and isopentane [15]. During each experimental course, the temperature varied The detail descriptions of the apparatus have been given in about ±1 K, and the reactants like O3 and NO2 were moni- our previous works. Here only a brief summary is given. The tored on line. After each experiment the reactor was flushed enclosure that housed the Teflon bag (100-L) and Ultra-violet using purified air for about 10 h with a 40 W blacklight lamps were constructed using wood. The inner surface of the lamp on. Relative light intensity in the chamber was meas- enclosure was coated with aluminum sheeting. Three ther- ured by the NO2 photolysis rate constant, which was ob- mometers with a precision of 0.2 K were placed in the cham- tained to be 0.1572 min1. ber. Four blacklight lamps (40×4 W, Model F40T8BL, with peak intensity at a wavelength of 350 nm) were used to sim- ulate the ground-level solar radiation in the experiments. 2 Model simulations During the reaction, the O3, NOx and CO concentrations were monitored in real time using the Model 49C-O3 Analyzer, the In order to compare the chamber experiments summarized Model 42C-NOx Analyzer and Model 48C-CO Analyzer, in Table 1 with our current understanding of atmospheric respectively. The linearity of above equipments is ±1% in the chemical reactions, calculations were carried out using the full detection range. The RH was measured by JinMin rela- Master Chemical Mechanism (MCM v3.1). Some chamber tive humidity analyzer with the accuracy of ±2.5%. dependent auxiliary mechanisms were established using O3-air, NOx-air and CO-NOx-air irradiation experiments, 1.2 Experimental reagents which include the wall effects of O3 and NO2, and the het- erogeneous reaction between H2O and NO2. By fitting the An ethanol gaseous mixture employed in the experiments was experimental data, the reaction constant (k) of the O3 wall 4474 Jia L, et al. Chin Sci Bull December (2012) Vol.57 No.34 Table 1 Initial experimental conditions for C2H5OH-NOx-air irradiations Exp.
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