The rapid growth in the global economy over the last decade as a consequence of increased industrial activity in regions such as India and China has resulted in an associated increase in the emission of reactive trace gases. This includes the nitrogen oxides (NO and NO2) which are important for determining the production efficiency of tropospheric ozone which can be detrimental to human health and crop production, and the acidification of rain via the production of HNO3. Other important sources of NOx include biomass burning (which occurs predominantly in Africa and South America over different times of the year), oxidation in the soil and lightning activity. Researchers at KNMI have used the continuous measurement record of tropospheric NO2 derived from both the Global Ozone Monitoring Experiment (GOME) and the Scanning Imaging Absorption spectrometer for Atmospheric Cartography (SCIAMACHY) for the period 1996-2006 to investigate the regional trends in such NOx emissions. By accounting for both the amplitude and frequency of the seasonal cycle they have derived the statistical significant trends in such emissions for the largest cities for the first time, where both increases (29±5% /yr Shanghai, 11±3% /yr Beijing) and decreases (-0.9±1% /yr Los Angeles, -3.6±1 /yr Köln) have been observed. Moreover, by selecting the month in the year where the maximum tropospheric NO2 concentrations occur they can also track the differences in the time of the biomass burning season from (e.g.) North to South Africa. For lightning NOx, the use of retrievals made using satellite pixels containing 100% cloud cover and a cloud-top pressure < 600hPa allows the quantification of the production of NO2 at high altitudes. By synthesizing these different findings the researchers are able determine the predominant NOx source for each region. Figure 1 below shows a composite derived from this data for the period 2003-2006, where the dominant emission sources are indicated.

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