Achieving the desired air quality standards and emission of greenhouse gases (or even particulate matter and sulphur oxides) requires enforcement of emission standards through an appropriate regulatory framework

Achieving the desired air quality standards and emission of greenhouse gases (or even particulate matter and sulphur oxides) requires enforcement of emission standards through an appropriate regulatory framework. Regulatory agencies such as EPA may enforce them for stationary sources of pollution (emissions) and/or mobile sources like automobiles, mass transit, buses, trucks, and ships. These "command and control" methods require businesses to take necessary pollution abatement actions. The emission control standards imposed may become increasingly tighter with time to facilitate continued improvements in air quality.

Would you advocate a direct "command and control" approach, or prefer to use other economic policy instruments to achieve those same emission levels? Or combine both? Please explain reasons for your choice.