Biogeochemical Rx in Troposphere Trace biogenic gases (NO, NO 2, N 2 O, CH 4, SO 2 ) more Rx than major constituents (N 2, O 2, Ar) NITROGEN & SULFUR Ozone formation associated with NO and NO 2 - anthropogenic and microbial production The Atmosphere - Chapter 3 Denitrification by bacteria fossil fuel agriculture & fertilizer use

“NO X ” [pronounced “knocks”] + O 3 formation [photochemical reactions] (3.6)NO 2 + hv → NO + O[dissociation of NO 2 by light, hv] (3.7)O + O 2 → O 3 [also requires sunlight] (3.8)NO 2 + O 2 ↔ NO + O 3 [net reaction] O 3 formation produces OH - radicals (3.9)O 3 + hv → O 2 + O( 1 D)[O( 1 D) = singlet of oxygen; highly reactive] (3.10)O( 1 D) + H 2 O → 2OH[OH - involved in tropospheric destruction of CH 4 ] OH radicals contribute to “acid” rain (3.26)NO 2 + OH → HNO 3 (nitric acid) (3.27)SO 2 + OH - → SO 3 + HO 2 (3.28)SO 3 + H 2 O → H 2 SO 4 (sulfuric acid) The Atmosphere - Chapter 3

Biogeochemical Rx in Stratosphere OZONE Formation [3.41] O 2 + hv  O + O [3.42]O + O 2  O 3 Destruction [3.43]O 3 + hv  O 2 + O [3.44]O + O 3  O 2 + O 2 (3.45)O 3 + OH - → HO 2 + O 2 (3.46)HO 2 + O 3 → OH - + 2O 2 (3.47)N 2 O → N 2 + O( 1 D) (3.49)N 2 O + O( 1 D) → 2NO (3.50)NO + O 3 → NO 2 + O 2 Etc… Accounts for most of the nm Accounts for most of the nm Warms the stratosphere Absorption of uVB, most damaging to living tissue Hydroxyl destroys ozone Nitrous oxide destroys ozone via release of O atom in an excited singlet state O(1D) The Atmosphere - Chapter 3

….Cl from CFC’s also eats away at O 3 in stratosphere (3.49) Cl + O 3 ↔ ClO + O 2 (w/subsequent Rxs) “Montreal Protocol” enacted in Jan is a success story from the perspective of an international effort to slow stratospheric O 3 depletion, but the recovery process has been very, very slow The Atmosphere - Chapter 3

Localization of O 3 thinning at the Poles Ozone typically "builds up" to higher values over the poles during the winter and early spring in each hemisphere. Air masses above the poles become isolated from the rest of the atmosphere during their winter and early spring seasons; i.e., the infamous "polar vortex” Chemical reactions in the enclosed air mass are enhanced b/c of isolation from lower-latitude air masses. Antarctic vortex over the south pole is more effective at isolation than the Arctic vortex. Polar stratospheric clouds are composed of ice crystals → greatly enriched in nitrogen oxide species ("NO x ") → react with Cl molecules forming ClONO 2 Springtime comes with UV radiation and drives O 3 degrading reactions Source: Dr. Ken Rubin, Dept. of Geology & Geophysics, U of Hawai’i

TH = time horizon over which the calculation is considered; a x = radiative efficiency due to a unit increase in atmospheric abundance of the substance (i.e., W m -2 kg -1 ); [x(t)] = time-dependent decay in abundance of the substance following an instantaneous release of it at time t=0. The denominator (a r )contains the corresponding quantities for the reference gas (i.e. CO 2 ).

Aerial Extent of summer Arctic Sea Ice, Summer 1979 Aerial Extent of summer Arctic Sea Ice, Summer 2009 Source: