Global and regional impacts of HONO on the chemical composition of clouds and aerosols 1Max Planck Institute for Chemistry, Division of Atmospheric Chemistry, Mainz, Germany
03 Feb 2014
2Institut für Physik der Atmosphäre, Johannes Gutenberg Universität, Mainz, Germany
3The Cyprus Institute, Nicosia, Cyprus
Received: 22 July 2013 – Published in Atmos. Chem. Phys. Discuss.: 09 September 2013 Abstract. Recently, realistic simulation of nitrous acid (HONO) based on the
HONO / NOx ratio of 0.02 was found to have a significant impact on the
global budgets of HOx (OH + HO2) and gas phase oxidation
products in polluted regions, especially in winter when other photolytic
sources are of minor importance. It has been reported that
chemistry-transport models underestimate sulphate concentrations, mostly
during winter. Here we show that simulating realistic HONO levels can
significantly enhance aerosol sulphate (S(VI)) due to the increased formation
of H2SO4. Even though in-cloud aqueous phase oxidation of dissolved
SO2 (S(IV)) is the main source of S(VI), it appears that HONO related
enhancement of H2O2 does not significantly affect sulphate because
of the predominantly S(IV) limited conditions, except over eastern Asia.
Nitrate is also increased via enhanced gaseous HNO3 formation and
N2O5 hydrolysis on aerosol particles. Ammonium nitrate is enhanced
in ammonia-rich regions but not under ammonia-limited conditions.
Furthermore, particle number concentrations are also higher, accompanied by
the transfer from hydrophobic to hydrophilic aerosol modes. This implies a
significant impact on the particle lifetime and cloud nucleating properties.
The HONO induced enhancements of all species studied are relatively strong in
winter though negligible in summer. Simulating realistic HONO levels is found
to improve the model-measurement agreement of sulphate aerosols, most
apparent over the US. Our results underscore the importance of HONO for the
atmospheric oxidizing capacity and corroborate the central role of cloud
chemical processing in S(IV) formation.
Revised: 26 November 2013 – Accepted: 16 December 2013 – Published: 03 February 2014
Citation: Elshorbany, Y. F., Crutzen, P. J., Steil, B., Pozzer, A., Tost, H., and Lelieveld, J.: Global and regional impacts of HONO on the chemical composition of clouds and aerosols, Atmos. Chem. Phys., 14, 1167-1184, doi:10.5194/acp-14-1167-2014, 2014.