Nitrous acid (HONO) emissions under real-world driving conditions from vehicles in a UK road tunnel

Louisa J. Kramer, Leigh R. Crilley, Thomas J. Adams, Stephen M. Ball, Francis D. Pope, William J. Bloss

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)
201 Downloads (Pure)


Measurements of atmospheric boundary layer nitrous acid (HONO) and nitrogen oxides (NOx) were performed in summer 2016 inside a city centre road tunnel in Birmingham, United Kingdom. HONO and NOx mixing ratios were strongly correlated with traffic density, with peak levels observed during the early evening rush hour as a result of traffic congestion in the tunnel. A day-time ΔHONO∕ΔNOx ratio of 0.85 % (0.72 % to 1.01 %, 95 % confidence interval) was calculated using reduced major axis regression for the overall fleet average (comprising 59 % diesel-fuelled vehicles). A comparison with previous tunnel studies and analysis on the composition of the fleet suggest that goods vehicles have a large impact on the overall HONO vehicle emissions; however, new technologies aimed at reducing exhaust emissions, particularly for diesel vehicles, may have reduced the overall direct HONO emission in the UK. This result suggests that in order to accurately represent urban atmospheric emissions and the OH radical budget, fleet-weighted HONO∕NOx ratios may better quantify HONO vehicle emissions in models, compared with the use of a single emissions ratio for all vehicles. The contribution of the direct vehicular source of HONO to total ambient HONO concentrations is also investigated and results show that, in areas with high traffic density, vehicle exhaust emissions are likely to be the dominant HONO source to the boundary layer.
Original languageEnglish
Pages (from-to)5231-5248
JournalAtmospheric Chemistry and Physics
Issue number9
Publication statusPublished - 5 May 2020


Dive into the research topics of 'Nitrous acid (HONO) emissions under real-world driving conditions from vehicles in a UK road tunnel'. Together they form a unique fingerprint.

Cite this