Ding Xiang, Huang Cheng, Liu Wenyang, Ma Dongxiang, Lou Shengrong, Li Qing, Chen Jun, Yang Huinan, Xue Chaoyang, Cheng Yafang, Su Hang
State Environmental Protection Key Laboratory of Formation and Prevention of Urban Air Pollution Complex, Shanghai Academy of Environmental Sciences, Shanghai 200233, China.
Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Department of Environmental Science and Engineering, Institute of Atmospheric Sciences, Fudan University, Shanghai 200433, China.
Environ Sci Technol. 2023 Mar 28;57(12):4751-4762. doi: 10.1021/acs.est.2c09386. Epub 2023 Mar 15.
Atmospheric nitrous acid (HONO) is an important precursor of atmospheric hydroxyl radicals. Vehicle emissions and heterogeneous reactions have been identified as major sources of urban HONO. Here, we report on HONO emissions from residential natural gas (RNG) for water and space heating in urban areas based on in situ measurements. The observed HONO emission factors (EFs) of RNG heating vary between 6.03 and 608 mg·m NG, which are highly dependent on the thermal load. The highest HONO EFs are observed at a high thermal load via the thermal NO homogeneous reaction. The average HONO EFs of RNG water heating in winter are 1.8 times higher than that in summer due to the increased thermal load caused by the lower inlet water temperatures in winter. The power-based HONO EFs of the traditional RNG heaters are 1085 times and 1.7 times higher than those of gasoline and diesel vehicles that meet the latest emission standards, respectively. It is estimated that the HONO emissions from RNG heaters in a typical Chinese city are gradually close to emissions from on-road vehicles when temperatures decline. These findings highlight that RNG heating is a non-negligible source of urban HONO emissions in China. With the continuous acceleration of coal-to-gas projects and the continuous tightening of NO emission standards for vehicle exhaust, HONO emissions from RNG heaters will become more prominent in urban areas. Hence, it is urgently needed to upgrade traditional RNG heaters with efficient emission reduction technologies such as frequency-converted blowers, secondary condensers, and low-NO combustors.
大气中的亚硝酸（HONO）是大气中羟基自由基的重要前体。车辆排放和非均相反应已被确定为城市HONO的主要来源。在此，我们基于现场测量报告了城市地区用于水加热和空间加热的居民用天然气（RNG）的HONO排放情况。观察到的RNG加热的HONO排放因子（EFs）在6.03至608 mg·m NG之间变化，这高度依赖于热负荷。通过热NO均相反应在高热负荷下观察到最高的HONO EFs。由于冬季进水温度较低导致热负荷增加，冬季RNG水加热的平均HONO EFs比夏季高1.8倍。传统RNG加热器基于功率的HONO EFs分别比符合最新排放标准的汽油车和柴油车高1085倍和1.7倍。据估计，在中国一个典型城市中，当温度下降时，RNG加热器的HONO排放正逐渐接近道路车辆的排放。这些发现突出表明，RNG加热是中国城市HONO排放中不可忽视的一个来源。随着煤改气项目的不断加速以及车辆尾气NO排放标准的不断收紧，RNG加热器的HONO排放在城市地区将变得更加突出。因此，迫切需要用变频鼓风机、二次冷凝器和低NO燃烧器等高效减排技术对传统RNG加热器进行升级。
