GLOBAL DISTRIBUTION OF TROPOSPHERIC OZONE

Zhang et al. [2010]

TES thermal IR satellite observations for 2006, seasonal means at 500 hPa

• Maximum values at northern mid-latitudes in spring-summer due to anthropogenic pollution;

• High values in tropical regions affected by seasonal biomass burning;

• Minimum values over tropical oceans due to chemical loss

OBSERVED RISE IN TROPOSPHERIC OZONEOBSERVED RISE IN TROPOSPHERIC OZONEOVER 20OVER 20thth CENTURY CENTURY

Preindustrialozone models

}Observations at mountain sites in Europe [Marenco et al., 1994]

Models underestimate the observed trend

RADIATIVE FORCING BY TROPOSPHERIC OZONE RADIATIVE FORCING BY TROPOSPHERIC OZONE COULD BE MUCH LARGER THAN IPCC VALUECOULD BE MUCH LARGER THAN IPCC VALUE

Standard model:

F = 0.44 W m-2

“Adjusted” model

(lightning and soil NOx decreased,

biogenic hydrocarbons increased):

F = 0.80 W m-2

Global simulation of late 19th century ozone observations [Mickley et al., 2001]

GLOBAL OZONE AND OH TRENDSMean mass-weighted tropospheric values computed from GEOS-Chem model

for present-day (PD), pre-industrial (PI), and last glacial maximum (LGM)

Ozone, ppb

OH, 105 molecules cm-3

PD PI LGMtwo different climatereconstructionsLee Murray, Harvard

MODEL INTERCOMPARISON OF OH TRENDSMODEL INTERCOMPARISON OF OH TRENDS

LGM to pre-industrial Pre-industrial to present

Using long-term trends of methylchloroform to infer trends in OH concentrations

Montzka et al. 2011

TRENDS IN GLOBALTROPOSPHERIC OHinferred from methylchloroform observations

IPCC, 2007

Montzka et al., 2011

TRENDS IN GLOBALTROPOSPHERIC OHusing observations of other gases

Montzka et al. [2011]