Fig. 2.

Change (%) in global tropospheric OH concentrations from 1980 to 2010, estimated with different Earth System Models (ESMs). The net change in OH (rightmost column) had contributions from increased emissions of nitrogen oxides and other precursors of tropospheric ozone (∆NO_x); increased emissions of methane (∆CH₄); accumulation of ozone-depleting substances now regulated under the Montreal Protocol (∆ODSs); emissions of particulate matter and its precursors (∆PM); and other undifferentiated changes attributed to underlying climate change as well as interactions among these separate factors (∆Other). The ODSs have contributed to the net increase in OH concentrations by depleting stratospheric ozone, thus allowing more UV radiation to penetrate into the troposphere and increase the rates of photochemical reactions that generate OH.

Modified from Stevenson et al. [36]