H2O2 Mysterious

One of the most interesting and important species in air is hydrogen peroxide (H2O2). Kok et al. (1978) suggested that H2O2 is an index of the HO2 radical concentration and better represents oxidation capacity than ozone. However, the relatively complicated and labor-intensive measurement technique hmits H2O2 measurements to very few sites and even then only occasionally (probably because of fixing to ozone as the oxidant leader species). 

Despite the decreasing emissions of many pollutants (SO2, dust, NO, VOCs), key impact factors such as oxidation capacity, acidity, toxicity and chmate forcing have not been reduced to the same extent but have remained constant or even increased. It is likely that our incomplete understanding of such relationships is because of insufficient budget estimation (i.e. taking into account all sources and sinks), which again strongly depends on time and space. 

Over the past 20 years, many H2O2 measurements have been carried out but almost always (with a very few exceptions) covering short measurement periods. The main findings of these studies are summarized as follows (Moller 2002b, 2009a, Lee et al. 2000, Gunz and Hoffmann 1990, and citations therein)  

Looking into details of the smoothed H2O2 ice core record (Fig. 2.86) it seems obvious to distinguish between several time periods coimected with different chemical climate, namely  

The extremely hot summer of 2003 led only to an increase of H2O2 by a factor of two above the trend line. The winter values at Hohenpeissenberg show no trend (mean of 0.14 ppb), whereas the summer values (mean of 0.51 ppb) show a trend of about +0.02 ppb yr remarkably similar to the trend found in Harwell (see above). Hence, the increase (based on monthly means) corresponds to 4% yr similar to the discussed increase in Greenland ice cores. The trend, however, is not significant and the few measurements support increasing atmospheric summer H2O2 concentrations. 

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