FIGURE 5.1: Schematic of biogeochemical cycling with human contributions included, illustrating the major gas-phase constituents in the lower atmosphere that are measured from space (shaded in gray). NO₂ and NO are encircled to represent equilibrium; their sum is referred to as NO_x. Note: BrO = bromine monoxide, CH₄ = methane, CO = carbon monoxide, h = Planck's constant, H₂O = water, HCHO = formaldehyde, HO₂ = hydroperoxyl, NO = nitric oxide, NO₂ = nitrogen dioxide, O(¹D) = electronically excited oxygen atoms, O₂ = molecular oxygen, O₃ = ozone, OH = hydroxide, RH = hydrocarbon species, SO₂ = sulfur dioxide, v = photon frequency.

SOURCE: Drawing by A. Thompson and K. Dougherty, Pennsylvania State University.