A local government decides to implement a subsidy for urban tree planting to combat air pollution. After the subsidy is introduced, the number of trees planted increases significantly. Which of the following best explains how this subsidy addresses the externalities associated with urban air quality?

A subsidy for urban tree planting helps improve air quality by encouraging more people to plant trees, which are natural air filters. When the government provides financial support, it reduces the cost for individuals and businesses, making it easier for them to participate in tree planting. This action addresses a negative externality, which is the problem of air pollution that affects everyone in the community, not just the tree planters. For example, if a neighborhood plants more trees, the air becomes cleaner, benefiting all residents by reducing health risks related to pollution. Therefore, the subsidy leads to a positive outcome for the community by promoting environmental health through increased greenery.