How do wind turbines pollute their environment?

Although the wind turbines do not pollute the environment directly, it is still able to pollute the environment indirectly. The maintenance, construction, and the assembly of the wind turbines would make use of equipment or machines that would emit some harmful substances. For example, the delivery of the materials, the turbine parts, and the other equipment would entail a lot of back and forth trips. The deliverer, from his vehicle, would sometimes emit smoke or gas from his vehicle that is dangerous to health. 

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