NO2 Photolysis Rate Research Articles

Measurements of tropospheric OH concentrations: A comparison of field data with model predictions

Using long path UV absorption spectroscopy we have measured OH concentrations close to the earth's surface. The OH values observed at two locations in Germany during 1980 through 1983 range from 0.7×106 to 3.2×106 cm-3. Simultaneously we measured the concentrations of O3, H2O, NO, NO2, CH4, CO, and the light non methane hydrocarbons. We also determined the photolysis rates of O3 and NO2. This allows calculations of OH using a zero dimensional time depdendent model. The modelled OH concentrations significantly exceed the measured values for low NO x concentrations. It is argued that additional, so far unidentified. HO x loss reactions must be responsible for that discrepancy.

Photoenhancement of the nitrous acid formation in the surface reaction of nitrogen dioxide and water vapor: Extra radical source in smog chamber experiments

AbstractThe surface reaction of NO2 and H2O vapor to emit HONO into the gas phase was studied in the evacuable and bakeable photochemical chamber under the irradiation of UV‐visible light (≳ 290 nm). Kinetic analysis of the NO, NO2, and HONO with the aid of computer modeling strongly suggested that the formation of HONO by the surface reaction is photoenhanced. When a linear regression was assumed, the photoenhancement factor defined by {(k′21/k21) − 1} was expressed as (6.8 ± 2.5)k1 under our experimental conditions, where k1 is the primary photolysis rate of NO2, and k21, k′21 are the second‐order‐equivalent rate constants of the HONO formation reaction in dark and under irradiation, respectively. The discussion was made that this photocatalitic enhancement of HONO formation would explain the nature of the extra OH radical flux in the smog chamber experiments, which has been discussed as “unknown radical source” and has still been unexplained by the surface dark reaction of NO2 and H2O to emit HONO.

Atmospheric gas phase loss processes for chlorobenzene, benzotrifluoride, and 4-chlorobenzotrifluoride, and generalization of predictive techniques for atmospheric lifetimes of aromatic compounds

The homogeneous gas phase atmospheric loss processes for chlorobenzene (CB), benzotrifluoride (BTF) and 4-chlorobenzotrifluoride (CBTF), compounds chemically and structurally similar to various classes of herbicides and pesticides currently in use, have been experimentally investigated by U.S. Environmental Protection Agency approved protocols. The rate constants, or upper limits thereof, for photolysis (under blacklight irradiation with an NO2 photolysis rate of 0.27 min−1) and reaction with OH radicals and O3 were determined. The rate constants obtained were: k(photolysis) <2.7×10−6 sec−1 for CBTF; k(O3 reaction) <5×10−21 cm3 molecule−1 sec−1 for all three of these aromatic compounds; and k(OH radical reaction)=(8.8±1.1)×10−13 cm3 molecule−1 sec−1 for CB; (4.4±1.1)×10−13 cm3 molecule−1 sec−1 for BTF; and (2.3±0.8)×10−13 cm3 molecule−1 sec−1 for CBTF. Estimated atmospheric lifetimes due to these reactions are calculated and their environmental implications discussed. A predictive technique is presented for estimating the rate constants for addition of OH radicals to aromatic rings.

Direct NO2 photolysis rate monitor.

An optically thin actinometer is described which measures the rate of photolysis of NO2 in air. Operating details of the device are reported together with a test in downtown Detroit. The result was that the instrument was more accurate than some of the other test parameters in the range 0–0.5 min−1. Applications to photochemical smog and stratospheric pollution problems are discussed.