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.
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