Photochemical renoxification of nitric acid on real urban grime.

Environmental science & technology (2012-12-15)
Alyson M Baergen, D J Donaldson
ABSTRACT

The fate of NO(x) (=NO + NO(2)) is important to understand because NO(x) is a significant player in air quality determination through its role in O(3) formation. Here we show that renoxification of the urban atmosphere may occur through the photolysis of HNO(3) deposited onto urban grime. The photolysis occurs 4 orders of magnitude faster than in water with J values at noon on July 1 in Toronto of 1.2 × 10(-3) s(-1) for nitrate on urban grime and 1.0 × 10(-7) s(-1) for aqueous nitrate. Photolysis of nitrate present on urban grime probably follows the same mechanism as aqueous nitrate photolysis, involving the formation of NO(2), OH, and possibly HONO. Thus NO(x) may be rapidly returned to the atmosphere rather than being ultimately removed from the atmosphere through film wash off.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Nitric acid, ACS reagent, 70%
Sigma-Aldrich
Nitric acid, 70%, purified by redistillation, ≥99.999% trace metals basis
Sigma-Aldrich
Nitric acid, puriss. p.a., reag. ISO, reag. Ph. Eur., for determinations with dithizone, ≥65%
Sigma-Aldrich
Nitric acid, puriss. p.a., 65.0-67.0%
Sigma-Aldrich
Nitric acid, ACS reagent, ≥90.0%
Supelco
Nitric acid concentrate, 0.1 M HNO3 in water (0.1N), eluent concentrate for IC
Sigma-Aldrich
Nitric acid, red, fuming, HNO3 >90 %
Sigma-Aldrich
Nitric acid, puriss. p.a., ≥65% (T)