Earlier quoted context omitted.
But, it is possible to measure the intensity of sound and how much that contributes to hearing loss. CDC has a handy chart on the effects of noise here: https://www.cdc.gov/nceh/hearing_loss/what_noises_cause_hear... . The existence of other sources of noise loud enough to damage hearing does not preclude banning leaf blowers.
Sound pressure levels are dependent on distance. A leaf blower might expose you to 90dB if you're using it, but someone stood 10 metres away would only be exposed to 70dB, which is well below the threshold for damage.
70 dBA is at the threshold for hearing damage (65-70 dBA range). It's below the OSHA limit of 85 dBA, but that is not the threshold for hearing damage, it's the threshold for acceptable [0] hearing damage.
[0] where "acceptable" means that a person exposed to 85 dBA for an average of 40-hrs per week for 10 years can still understand conversational speech in an ideal environment.