Figure 7 maps the global distribution of ratios of tropospheric to total column . It shows that anthropogenic emissions are the primary source of over land. As can be seen from the figure, the high ratios occur in polluted urban areas, ranging from 0.5 to 0.8, due to higher anthropogenic emitted from the burning of fossil fuels for transportation and industrial activities. Higher ratios also occur in the Persian Gulf region due to the oil industry and maritime shipping, and in savannah fires in South America, Africa, and Indonesia due to biomass burning, and in the regions of the southern Sahara Desert due to soil emission. Over land, generally, the lower ratios occur in the Sahara Desert, Tibetan Plateau, Siberia, Greenland, and Antarctica, where is derived mainly from natural sources. In some of the EAS regions, the ratios are higher than 0.8, which implies that the anthropogenic emission is the dominant source of atmospheric , whereas despite the abatement of anthropogenic emissions over North America, the ratios are still maintained at a higher level (). For the remote oceans, the ratios are very low, mainly because there is almost no anthropogenic activity and is hardly ever transported to the remote oceans from land due to its shorter lifetime.