Sources of atmospheric nitrous acid: State of the science, current research needs, and future prospects

Figures & data

Figure 1. A schematic sketch over the chemical processes acting as sources and sink for nitrous acid (HONO) in the lower atmosphere. The processes occurring only in presence of solar radiation are reported in the yellow section, whereas the processes producing and removing HONO mainly during daytime are showed in the blue section. Finally, the gray section includes the sources and sinks of HONO operating similarly both during daytime and nighttime.

Table 1. Main reaction mechanisms proposed for the heterogeneous NO₂ hydrolysis

Surface	Reaction Mechanism	Reference
Pyrex glass		Jenkin et al., 1988
Borosilicate glass		Finlyson-Pitts et al., 2003
Mineral dust		Gustafsson et al., 2009
Borosilicate glass		Ramazan et al., 2004

Table 2. NO₂ uptake coefficients (γ_NO2) of different organic surfaces under UV irradiation

	RH	λ	[NO2]
Surface	(%)	(nm)	(ppb)	γNO2	Reference
Humic acid (soil)	20	300–700	20	2 × 10^−5	Stemmler et al., 2006
Humic acid (coating)	26	400–750	˜10	˜1.5 × 10^−5	Stemmler et al., 2007
Humic acid (aerosol)	26	400–750	˜10	˜5.5 × 10^−6	Stemmler et al., 2007
Benzophenone/catechol	76	300–420	20	5.1 × 10^−6	George et al., 2005
Pyrene/KNO3		300–420	30	2.7 × 10^−6	Ammar et al., 2010
Benzophenone/catechol	14	300–420	20	2.5 × 10^−6	George et al., 2005
Benzophenone/catechol	Dry	300–420	20	2.4 × 10^−6	George et al., 2005
Anthracene	56	300–420	20	2.3 × 10^−6	George et al., 2005
Fluoranthene surface	<5	300–420	25	2.0 × 10^−6	Cazoir et al., 2014
Catechol	42	300–420	20	1.8 × 10^−6	George et al., 2005
Catechol	Dry	300–420	20	1.4 × 10^−6	George et al., 2005
Catechol/anthracene	46	300–420	20	1.3 × 10^−6	George et al., 2005
Anthracene	Dry	300–420	20	1.2 × 10^−6	George et al., 2005
Benzophenone	Dry	300–420	20	6.5 × 10^−7	George et al., 2005
Soot surface	30	300–420	150	5.0 × 10^−7	Monge et al., 2010a

Notes: RH = relative humidity; [NO₂] = concentration of NO₂; λ = wavelength.

Figure 2. Schematic sketch of the major components related to the differential optical absorption spectroscopy (DOAS) system.

Figure 3. Schematic sketch of the semiautomatic HONO instrument based on reverse-phase HPLC analysis, followed by UV absorption detection.

Figure 4. Schematic sketch of the long-path absorption photometric (LOPAP) technique.

Jenkin, M.E., R.A. Cox, and D.J. Williams. 1988. Laboratory studies of the kinetics of formation of nitrous acid from the thermal reaction of nitrogen dioxide and water vapour. Atmos. Environ. 22:487–498. doi:10.1016/0004-6981(88)90194-1

 Web of Science ®Google Scholar

Finlayson-Pitts, B.J., L.M. Wingen, A.L. Sumner, D. Syomin, and K.A. Ramazan. 2003. The heterogeneous hydrolysis of NO2 in laboratory systems and in outdoor and indoor atmospheres: An integrated mechanism. Phys. Chem. Chem. Phys. 5:223–242. doi:10.1039/b208564j

 Web of Science ®Google Scholar

Gustafsson, R.J., G. Kyriakou, and R.M. Lambert. 2009. The molecular mechanism of tropospheric nitrous acid production on mineral dust surfaces. Chem. Phys. Chem. 9:1390–1393. doi:10.1002/cphc.200800259

 Web of Science ®Google Scholar

Ramazan, K.A., D. Syomin, and B.J. Finlayson-Pitts. 2004. The photochemical production of HONO during the heterogeneous hydrolysis of NO2. Phys. Chem. Chem. Phys. 6:3836–3843. doi:10.1039/b402195a

 Web of Science ®Google Scholar

Stemmler, K., M. Ammann, C. Donders, J. Kleffmann, and C. George. 2006. Photosensitized reduction of nitrogen dioxide on humic acid as a source of nitrous acid. Nature 440:195–198. doi:10.1038/nature04603

 PubMed Web of Science ®Google Scholar

Stemmler, K., M. Ndour, Y. Elshorbany, J. Kleffmann, B. D’Anna, C. George, B. Bohn, and M. Ammann. 2007. Light induced conversion of nitrogen dioxide into nitrous acid on submicron humic acid aerosol. Atmos. Chem. Phys. 7:4237–4248. doi:10.5194/acp-7-4237-2007

 Web of Science ®Google Scholar

George, C., R.S. Strekowski, J. Kleffmann, K. Stemmler, and M. Ammann. 2005. Photoenhanced uptake of gaseous NO2 on solid organic compounds: A photochemical source of HONO? Faraday Discuss. 130:195–210. doi:10.1039/b417888m

 PubMed Web of Science ®Google Scholar

Ammar, R., M.F. Monge, C. George, and B. D’Anna. 2010. Photoenhanced NO2 loss on simulated urban grime. Chemphyschem 11:3956–3961. doi:10.1002/cphc.201000540

 PubMed Web of Science ®Google Scholar

Cazoir, D., M. Brigante, R. Ammar, B. D’Anna, and C. George. 2014. Heterogeneous photochemistry of gaseous NO2 on solid fluoranthene films: A source of gaseous nitrous acid (HONO) in the urban environment. J. Photochem. Photobiol. A Chem. 273:23–28. doi:10.1016/j.jphotochem.2013.07.016

 Web of Science ®Google Scholar

Monge, M.E., B. D’Anna, and C. George. 2010a. Nitrogen dioxide removal and nitrous acid formation on titanium oxide surfaces—An air quality remediation process? Phys. Chem. Chem. Phys. 12:8991–8998. doi:10.1039/b925785c

 PubMed Web of Science ®Google Scholar