I recently got into a online discussion with someone who made the ridiculous argument that CO2 (carbon dioxide) can not be classified as a pollutant. Below are the reasons he gave that it is not a pollutant and my responses:
".. benign gas..."
Many pollutants are "benign" at low levels. The are several ways in which CO2 is not benign at higher concentrations.
Many pollutants (maybe even most) occur naturally - asbestos, mercury, sulphur, radiation,
"helps to maintain the earth at a temperature suitable for life"
Ozone as it exists in the atmosphere also helps to maintain life on the earth. But it is also considered a pollutant.
"...essential to the growth of all plants..."
Nitrates are essential to plant growth. Sulphur is an essential element for cell growth. But both are considered pollutants.