Ozone photochemical production

Unhealthy concentrations of ozone due to photochemical production from nitrogen oxides are a daily occurrence for millions of people who live in large urban centers. This is especially true for inhabitants of large cities in the warmer... 

Oxidation-reduction reactions in water are dominated by the biological processes of photosynthesis and organic matter oxidation. A very different set of oxidation reactions occurs within the gas phase of the atmosphere, often a consequence of photochemical production and destruction of ozone (O3). While such reactions are of great importance to chemistry of the atmosphere - e.g., they limit the lifetime in the atmosphere of species like CO and CH4 - the global amount of these reactions is trivial compared to the global O2 production and consumption by photosynthesis and respiration. 

In addition to observations in Los Angeles, Blumenthal and White have reported measurements of a power-plant plume and an urban plume 35 and 46 km downwind from St. Louis, Nfissouri. Bgute 4-25 shows the evidence of extensive ozone buildup in the urban plume. Simultaneous measurements of scattering coefficient, 6>cat, trace the spread and dilution of suspended particulate material. It is interesting that in the urban plume, which spreads to 20 km in width, the ozone increases while the particulate matter decreases this suggests considerable photochemical production at an altitude of 750 m. Contrary to the statements of Davis and co-workers reported above, the power-plant plume causes a decrease, rather than an increase, in ozone. Nitric oxide in the plume reacts with the ozone as it mixes. This is clearly indicated by the distribution of particulate matter, which acts as a tracer. 

The first step (Reaction 1-120) produces the highly reactive O radical, which can either recombine to form O2, or react with O2 to form O3. Somehow a significant fraction (more than the equilibrium fraction) goes to O3, often with the help of molecules such as N2. Hence, the photochemical production of ozone is another example of nature manipulating thermodynamics and kinetics to produce something that "should not be there," similar to photosynthesis. 

Photochemical production and decomposition of ozone, and the ozone hole... 

Ozone in the atmosphere is a good example of photochemical reactions. Atmospheric ozone is not due to equilibrium. The production and decomposition of ozone are largely by photochemical process, and the concentration of ozone in the stratosphere is at steady state, controlled by the kinetics of photochemical production and decomposition. 

Skov, H., A. H. Egelov, K. Granby, and T. Nielsen, Relationships between Ozone and Other Photochemical Products at LI. Valby, Denmark, Atmos. Environ., 31, 685-691 (1997). 

We simulated a period of three years (not nudged) to investigate the climatology of the tropospheric ozone budget and the contribution by STE. We focus on the NH where the ozone-PV relation derived from MOZAIC is applied. Figure 4 displays the seasonality of cross-tropopause transports, photochemical production/destruction, dry deposition and the tropospheric content of ozone. 

Also shown are the separate contributions by ozone originating from the stratosphere (03s) and from photochemical production in the troposphere (03t). The data are summarized in Table 2. We note that both the downward flux of 03s and the tropospheric content of 03t in the NH are about 10% larger compared to the previous model version [18] due to model changes mentioned in Section 3. 

In the literature a wide range of estimates regarding the influx of ozone from the stratosphere into the troposphere is presented, derived by many different methods. Some studies report an annual flux between 200-870 Tg 03 yr 1 globally, whereas other studies report a flux between 500 and 1000 Tg 03 yr 1 for the NH only. With our model we estimate for the NH a net downward flux from the stratosphere of 580 Tg 03 yr1, which is partly balanced by an upward flux of ozone from photochemical production in the troposphere of 210 Tg 03 yr1, yielding a net downward cross-tropopause ozone transport of 370 Tg 03 yr 1. Globally, these values are 950, 370 and 580 Tg 03 yr 1, respectively. (Note that the troposphere-to-stratosphere ozone flux in the... 

The main objective of the PAUR I project was to investigate how increased penetration of UV-B solar radiation through the atmosphere, resulting from stratospheric ozone depletion, affects photochemical production and chemical transformation of ozone and other photochemically active species in the lower atmospheric layers. 

Guicherit R, van Dop H (1977) Photochemical production of ozone in western Europe (1971-1978) and its relation to meteorology. Atmos Environ 11 145-155... 

Die increasing Tg at altitudes above the tropopause is largely due to the photochemical production of ozone via the well-known reactions ... 

Photochemical production of ozone in the troposphere occurs from the photolysis of nitrogen dioxide (N02) during the daytime, producing oxygen atoms (O) ... 

The absorption cross sections for NO2 and the corresponding quantum yields are given in Table 8 and 9, respectively. The photolysis of NO2 has been investigated intensively over the last 40 years because of its critical role in the formation of ozone in the polluted tropospheric boundary layer [56-63]. The three reactions of Eqs. 33 and 34 form the basis for the photochemical production of ozone. If one considers only these three reactions, then the photo-stationary state (or photochemical steady-state approximation) can be invoked around the oxygen atom as follows ... 

A major component of the reactive hydrocarbon loading are the biogenic hydrocarbons. As previously indicated, the hydrocarbon oxidation chemistry is integral to the production of ozone. Globally, the contribution of NMHC to net photochemical production of ozone is estimated to be about 40%. ... 

However, the photochemical production of ozone on a small scale represents a potential application of the novel incoherent Xe2 excimer lamps. This was first demonstrated by Eliasson and Kogelschatz (1991), and on laboratory and preparative scales by Laszlo et al. (1998) and by Hashem et al. (1997). The latter research group realized the simultaneous generation of ozone in the gas phase and its transfer to the aqueous phase followed by the VUV irradiation of this water by... 

A possible explanation is that, while the photochemical production and loss of ozone is much larger than the transport contribution, the sum of the production and loss provides a small net sink to balance the transport source. At this time the accurate data necessary for such calculations are not available. 

Globally, the oxides of nitrogen, NO (nitric oxide), NO2 (nitrogen oxide), and N2O (nitrous oxide), are key species involved in the chemistry of the troposphere and stratosphere. NO and N2O are produced mostly by microbial soil activity, whereas biomass burning is also an important source of NO. Nitric oxide is a species involved in the photochemical production of ozone in the troposphere, is involved in the chemical produaion of nitric acid, and is an important component of acid precipitation. Nitrous oxide plays a key role in stratospheric ozone depletion and is an important greenhouse gas, with a global warming potential more than 200 times that of CO2. 

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