High Gaseous Nitrous Acid (HONO) Emissions from Light-Duty Diesel Vehicles

Abstract

Nitrous acid (HONO) plays an important role in the budget of hydroxyl radical (•OH) in the atmosphere. Vehicular emissions are a crucial primary source of atmospheric HONO, yet remain poorly investigated, especially for diesel trucks. In this study, we developed a novel portable online vehicular HONO exhaust measurement system featuring an innovative dilution technique. Using this system coupled with a chassis dynamometer, we for the first time investigated the HONO emission characteristics of 17 light-duty diesel trucks (LDDTs) and 16 light-duty gasoline vehicles in China. Emissions of HONO from LDDTs were found to be significantly higher than previous studies and gasoline vehicles tested in this study. The HONO emission factors of LDDTs decrease significantly with stringent control standards: 1.85 ± 1.17, 0.59 ± 0.25, and 0.15 ± 0.14 g/kg for China III, China IV, and China V, respectively. In addition, we found poor correlations between HONO and NOx emissions, which indicate that using the ratio of HONO to NOx emissions to infer HONO emissions might lead to high uncertainty of HONO source budget in previous studies. Lastly, the HONO emissions are found to be influenced by driving conditions, highlighting the importance of conducting on-road measurements of HONO emissions under real-world driving conditions. More direct measurements of the HONO emissions are needed to improve the understanding of the HONO emissions from mobile and other primary sources.

Contribution of Vehicle Emission and NO2 Surface Conversion to Nitrous Acid (HONO) in Urban Environments: Implications from Tests in a Tunnel

“…The measured HONO/CO 2 ratio (v/v) for on-road vehicles was (2.9 ± 1.6) × 10 –5 on average, which was slightly higher than (2.6 ± 0.5) × 10 –5 measured by Kurtenbach et al at Kiesberg Tunnel, Germany, in 1997 . HONO in vehicle exhaust mainly comes from the heterogeneous conversion of NO 2 on the particle in vehicle exhaust and catalyst surface. ,− Based on observations at 61 European urban roadside monitoring sites, the NO x emission from vehicles declined significantly since 1995, but the NO 2 concentration had increased by ∼5 μg m –3 from 1995 to 2015 . Grange et al suggested that the increase of NO 2 in vehicle exhaust was related to the implementation of higher emission standards .…”

“…Grange et al suggested that the increase of NO 2 in vehicle exhaust was related to the implementation of higher emission standards . A recent study was also found that NO 2 /NO x in the gasoline exhaust from China III to China VI was much higher than the value reported by Kurtenbach et al Euro III standards were not implemented in Europe in 1997, and more than 75% of on-road vehicles in 2019 met China IV (identical to Euro IV) in China . With the upgrade of emission standards, NO 2 /NO x in vehicle exhaust increases rather than decreases, making the HONO/CO 2 measured in this study close to Kurtenbach et al Therefore, the higher HONO/NO x ratio for on-road vehicles in this study might be related to the fact that NO 2 emission reduction from the vehicles is not proportional to reducing NO x emission with higher emission standards.…”

“…It significantly affects atmospheric • OH budget and photochemical oxidation processes, especially in the early morning, − and may also play vital roles even in the formation of haze and ozone. − HONO in the atmosphere can come from both primary emission and secondary formation. Its secondary sources include gas-phase reactions, ,− the reaction of NO 2 on surfaces, − and photolysis of HNO 3 or NO 3 – , , while its direct emission sources include biomass burning, − soil emission, − and vehicle exhaust. − The relative contribution of these sources to ambient HONO, however, is often poorly understood. ,,− …”

Amplified role of potential HONO sources in O<sub>3</sub> formation in North China Plain during autumn haze aggravating processes

“…HONO sources can be generally classified into three categories, i.e., direct emissions and homogeneous and heterogeneous reactions. Direction emissions are mainly from traffic (Kramer et al, 2020;Kurtenbach et al, 2001;Liao et al, 2021), soil (Kubota and Asami, 1985;Oswald et al, 2013;Wu et al, 2019;Xue et al, 2021), biomass burning (Cui et al, 2021;Rondon and Sanhueza, 1989;Theys et al, 2020), and indoor combustion processes (Klosterkother et al, 2021;Liu et al, 2019;Pitts et al, 1985). The reaction of nitric oxide (NO) with OH (Pagsberg et al, 1997;Stuhl and Niki, 1972) is usually thought to be the dominant homogeneous reaction and is significant during daytime, but may be neglected at night due to low OH concentrations, other minor homogeneous HONO sources including nucleation of NO 2 , H 2 O, and NH 3 (Zhang and Tao, 2010), via the photolysis of orthonitrophenols (Bejan et al, 2006;Chen et al, 2021;Lee et al, 2016), via the electronically excited NO 2 and H 2 O (Crowley and Carl, 1997;Dillon and Crowley, 2018;Li et al, 2008) and via HO 2 q H 2 O + NO 2 reaction (Li et al, 2015(Li et al, , 2014Ye et al, 2015).…”

Amplified role of potential HONO sources in O<sub>3</sub> formation in North China Plain during autumn haze aggravating processes

“…HONO sources can be generally classified into three categories, i.e., direct emissions, homogeneous and heterogeneous reactions. Direction emissions are mainly from traffic (Kramer et al, 2020;Kurtenbach et al, 2001;Liao et al, 2021), soil (Kubota and Asami, 1985;Oswald et al, 2013;Wu et al, 2019;Xue et al, 2021), biomass burning (Cui et al, 2021;Rondon and Sanhueza, 1989;Theys et al, 2020) and indoor combustion processes (Klosterkother et al, 2021;Liu et al, 2019;Pitts et al, 1985). The reaction of nitric oxide (NO) with OH is usually thought as the dominant homogeneous reaction and is important during daytime but could be neglected at night due to low OH concentrations.…”