Pl. Cooper et Jpd. Abbatt, HETEROGENEOUS INTERACTIONS OF OH AND HO2 RADICALS WITH SURFACES CHARACTERISTIC OF ATMOSPHERIC PARTICULATE MATTER, Journal of physical chemistry, 100(6), 1996, pp. 2249-2254
The heterogeneous interactions of OH and HO2 radicals with a number of
surfaces characteristic of atmospheric particulate matter have been s
tudied by using a low-temperature flow tube coupled to a resonance flu
orescence detector. In particular, the mass accommodation coefficients
(a) of both OH and HO2 on supercooled sulfuric acid solutions have be
en measured: for OH, alpha > 0.2 for 45-96 wt % solutions from 220 to
295 K, and for HO2, alpha > 0.2 on 55 wt % solutions doped with 0.1 M
CuSO4 at 223 K. Radical uptake coefficients (gamma) were also measured
on a variety of solid surfaces prevalent in the atmosphere: water ice
, NH4HSO4 and (NH4)(2)-SO4. On water ice, although it was found that t
he uptake coefficients of both OH and HO2 were relatively small on con
ditioned surfaces (gamma(OH) = 0.03 +/- 0.02 from 205 to 230 K, gamma(
HO2) = 0.025 +/- 0.005 at 223 K), it was observed that the OH uptake c
oefficient could be significantly increased by either adsorbing HNO3 t
o the surface or melting the ice surface by exposure to relatively hig
h partial pressures of HCl. Similarly, on conditioned (NH4)(2)SO4 and
NH4HSO4 surfaces at room temperature, the OH uptake coefficient is rel
atively small, gamma(OH) < 0.03. Nevertheless, the uptake coefficient
can be significantly increased (gamma(OH) > 0.2) by exposing the surfa
ce to relatively low partial pressures of an organic species, 1-hexano
l.