I had a hunch that was the case. I can't imagine the people of the time being concerned about the air being polluted.
Not in the popular sentiment, but the first known scientific prediction of potential global warming was by Svante Arrhenius at the end of the 19th century.
I think the wording kind of gives it away. I don't think cars or other vehicles would be described as "horseless carriages", but rather "gas-powered carriages" or something that suggests what replaces the horse.