Studies collected on this site describe the overlapping reasons for communities to move beyond two-stroke gas-powered outdoor equipment:

These inefficient engines are hyper-polluting, putting out more hydrocarbon emissions of certain sorts than do cars that can weigh 100 times as much.
The small-particulate emissions they produce, and the haze of particulates that their high-speed winds blow up from the ground, are hazardous to the community in general and especially to the workers who spend hours each day within breathing range of the equipment.
Radically cleaner, safer, quieter less-polluting options are available, with the rapidly improving technology of battery powered equipment. In almost every other realm in which two-stroke engines once prevailed, from scooters to watercraft, they have largely been banned or simply overtaken by modern alternatives.

Beyond all this, the most obvious trait of leaf blowers in particular is their noise. In a new paper for the Journal of Environmental and Toxicological Studies, published at the scientific site Sci Forschen, Erica Walker and Jamie Banks argue that there is something distinctive about the auditory qualities of leafblowers that makes their sound-footprint so dominant and potentially dangerous.

A major theme of their paper is that the most disruptive component of leafblower noise is its low-frequency sound waves--rather than the high-frequency sounds that come from, for example, a dental drill. A high-frequency whine can obviously be annoying. But low-frequency sound waves travel a much greater distance, and pose a greater health risk. As Walker and Banks put it, (emphasis added):

According to manufacturer reports, the sound pressure levels of these machines exceed 95 A-weighted decibels (dB[A]) at the ear of the operator [a level at which regular exposure can cause permanent hearing loss] and typically 65-80 dB(A) at 50 feet. Comparing these levels to daytime sound standards set by the World Health Organization (WHO)- these levels are upwards of 15 dB(A) higher than the recommended 55 dB(A)....

Adverse health effects from sound include auditory effects such as hearing loss and tinnitus, and non auditory effects such as reduced cognitive performance and mental health, sleep disruption, ischemic heart disease, myocardial infarction, and hypertension. Low frequency sound components are considered to have more severe adverse health effects compared with higher frequency components. Adverse effects from sources of sound with low frequency components may occur at levels below 30 dB(A). Lower decibel standards are recommended for sources with low frequency components compared with other sources.

Read the full study for more details. At face value one implication is that the unmuffled two-stroke engines that proliferate in many neighborhoods are dangerous most of all to the workers using them. But another that the long-term damage to the surrounding community may be even greater than standard measures indicate, because the low-frequency waves travel farther than other kinds of sound, and can do more harm to those in their path.