Identify the transitional word/s or phrase/s in the following sentence/s.  Identify the type of transition. Sulfur dioxide (SO2) from human sources comes primarily from smelters and coal burning power plants. Hot sulfur dioxide also originates from natural sources, including volcanic emissions and sea spray. Nitrogen oxides come primarily from automobile exhaust and other combustion processes, and some is created by lightning and soil microbes. In past decades, to reduce air pollution in areas near power plants, utilities built tall smoke stacks to vent emissions high up into the air, away from local communities. As these smokestacks push emissions up into the atmosphere, the emissions react with the water particles in the air and are transported long distances by the wind. Because the prevailing winds in the U. S. are from West to East, eastern regions are more affected by acidic precipitation, even though the source of the emissions may be many miles away. However, nitrogen oxides from automobile exhaust contribute to acidic precipitation in all densely populated areas with heavy traffic.  ​