The environmental effects of lockdown
ROO + HO 2 → ROOH + O 2
(9)
Net: RH + OH + HO 2 → ROOH + O 2
(10)
In addition, HO 2 can also react with ozone, regenerating OH radicals and producing more O 2 (11).
HO 2 + O ₃ → OH + 2O 2
(11)
Reactions (1,4,5,6 and 11) Net: CO + O3 → CO2 + O2
(12)
In regions with high concentrations of NO x and little presence of VOCs, a formation and loss cycle of ozone is set up leading to no net loss or gain of ozone. Nitrogen dioxide is photolyzed, breaking down into atomic oxygen and nitrogen monoxide (13). Nitrogen monoxide reacts readily with ozone to produce nitrogen dioxide and O 2 (14). As, the atomic oxygen can also react with O 2 as shown in reaction (3), there is no net loss of any gases.
3 P)
NO 2 + hv → NO + O(
(13)
NO + O ₃ → O 2 + NO 2 (14) However, in the presence of VOCs, NO gas interrupts in the degradation reactions of VOC and react with peroxy radicals, ROO andHO 2 , to formNO 2 (15, 16). Then the photolysis of NO 2 and subsequent reaction (13) and (3) result in a net gain of O 3 .
NO + HO 2 → OH + NO 2
(15)
NO + ROO → RO + NO 2
(16)
The highly reactive RO radical then reacts with O 2 to produce more of the hydroperoxyl radical, HO 2 (17). It is shown in the reaction below using methane as the VOC pollutant.
CH 3 O + O 2 → HCHO + HO 2
(17)
The mechanisms for O 3 production rely on the regeneration of hydroperoxyl and hydroxyl radicals (Lu, 2019) and so the reaction chain set out above can be stopped when OH radicals are used up by reacting with NO 2 and the HO 2 radical reacts with itself (these are termination steps) (18, 19). The products are then taken out from the atmosphere by wet deposition, 9 whereby the gases dissolve into water during precipitation and are deposited along with water on the Earth’s surface.
NO 2 + OH + M → HNO 3 + M
(18)
2HO 2 → H 2 O 2 + O 2
(19)
In addition to the other reaction cycles the presence of NO x gases in the atmosphere leads to these reactions. However, there is no net loss or gain of ozone.
Nitrogen dioxide freely reacts with ozone to produce a nitrate radical (20), which is quickly photolyzed, splitting in 2 separate ways (21, 22), however the production of atomic oxygen occurs around 90% of the time. 10 Reaction (20) leads to reaction (3) to produce ozone.
NO 2 + O 3 → NO 3 + O 2
(20)
9 Lu, X., Zhang, L., Shen, L. ‘ Meteorology and climate influences in tropospheric ozone: a review of Natural sources, Chemistry and Transpo rt patterns’ . (2015, July 12). (n.p.). https://link.springer.com/content/pdf/10.1007/s40726- 019-00118-3.pdf. 10 Atkinson, R. ‘ Atmospheric Chemistry of VOC and NOx’ . (2000). Atmospheric Environment 34. https://ysuatmsymp.github.io/papers/SNU/SNU_06.pdf.
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