Nitrous
acid (HONO) significantly contributes to OH radicals in
the atmosphere, whereas the HONO sources need to be urgently further
explored. The photolysis of solid nitroaromatic compounds (Ar-NO2), including nitrophenols (NPs) and nitro-polycyclic aromatic
hydrocarbons (NPAHs), was investigated in a cylindrical reactor coupled
to a NOx analyzer at the ambient pressure. The formation
of HONO and NOx (NOx = NO2 + NO) by the photolysis of five NPs and four NPAHs was quantified.
HONO and NO formations from Ar-NO2 were obviously enhanced
under irradiation. For NPs, the Ar-NO2 photolysis frequency
for HONO (J
Ar‑NO2→HONO) and NO (J
Ar‑NO2→NO) formations varied in the range of (0.34–4.16) × 10–7 and (0.38–3.21) × 10–7 s–1, respectively. For NPAHs, J
Ar‑NO2→HONO and J
Ar‑NO2→NO were measured to be
(0.02–2.01) × 10–5 and (0.001–1.59)
× 10–4 s–1, respectively.
The photolysis of Ar-NO2 in aerosols was estimated to establish
a HONO source strength lower than 17 ppt·h–1, suggesting that the photolysis of Ar-NO2 may not well
explain daytime HONO source strength in the atmosphere.
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