Department of Civil and Environmental Engineering, University of California - Davis, Davis, California 95616, United States.
Department of Biological and Agricultural Engineering, University of California - Davis, Davis, California 95616, United States.
Environ Sci Technol. 2021 Mar 2;55(5):2820-2830. doi: 10.1021/acs.est.0c04962. Epub 2021 Feb 8.
Biogas consisting primarily of methane (CH) and carbon dioxide (CO) can be upgraded to a transportation fuel referred to as renewable natural gas (RNG) by removing CO and other impurities. RNG has energy content comparable to fossil compressed natural gas (CNG) but with lower life-cycle greenhouse gas (GHG) emissions. In this study, a light-duty cargo van was tested with CNG and two RNG blends on a chassis dynamometer in order to compare the toxicity of the resulting exhaust. Tests for reactive oxygen species (ROS), biomarker expressions (CYP1A1, IL8, COX-2), and mutagenicity (Ames) show that RNG exhaust has toxicity that is comparable or lower than CNG exhaust. Statistical analysis reveals associations between toxicity and tailpipe emissions of benzene, dibenzofuran, and dihydroperoxide dimethyl hexane (the last identification is considered tentative/uncertain). Further gas-phase toxicity may be associated with tailpipe emissions of formaldehyde, dimethyl sulfide, propene, and methyl ketene. CNG exhaust contained higher concentrations of these potentially toxic chemical constituents than RNG exhaust in all of the current tests. Photochemical aging of the vehicle exhaust did not alter these trends. These preliminary results suggest that RNG adoption may be a useful strategy to reduce the carbon intensity of transportation fuels without increasing the toxicity of the vehicle exhaust.
沼气主要由甲烷（CH）和二氧化碳（CO）组成，可以通过去除 CO 和其他杂质来升级为一种称为可再生天然气（RNG）的运输燃料。RNG 的能量含量与化石压缩天然气（CNG）相当，但生命周期温室气体（GHG）排放量较低。在这项研究中，一辆轻型货车在底盘测功机上使用 CNG 和两种 RNG 混合物进行了测试，以比较产生的废气的毒性。活性氧物种（ROS）、生物标志物表达（CYP1A1、IL8、COX-2）和致突变性（Ames）的测试表明，RNG 废气的毒性与 CNG 废气相当或更低。统计分析揭示了毒性与苯、二苯并呋喃和二氢过氧化物二甲己烷（最后一个鉴定被认为是暂定/不确定）排气管排放之间的关联。进一步的气相毒性可能与甲醛、二甲基硫、丙烯和甲基乙烯酮的排气管排放有关。在所有当前的测试中，CNG 废气比 RNG 废气含有更高浓度的这些潜在有毒化学物质。车辆废气的光化学老化并没有改变这些趋势。这些初步结果表明，采用 RNG 可能是减少运输燃料碳强度而不增加车辆废气毒性的有效策略。
