Whether or not automobile manufacturers support the regulations isn't relevant to Erin's main point, which is that these regulations will reduce PAH levels and save thousands of lives.

Erin's argument is only based on heart and lung disease, not on any other diseases. So pointing out that no causal link has been shown between PAHs and other diseases wouldn't be a relevant counter to her argument.

Not a good counter. Knowing that a decline in PAHs could happen on its own if automobile use declines, which we don't know will necessarily happen, doesn't weaken Erin's claim that passing these regulations now would save thousands of lives.

This is a strong counter. It tells us that these regulations won't actually work to significantly reduce PAH levels, since the regulations only target exhaust and not tires. So Erin's claim that the regulations would save thousands of lives seems much less likely.

This claim doesn't affect Erin's argument. Her argument isn't based on a link between PAHs and cancer, but between PAHs and lung and heart disease.