These local concentrations of unvaccinated children pose a growing risk to public health.

未接种疫苗的孩子集中在一个地区给公共健康造成的风险越来越大。

Trees can also reduce the amount of exhaust gases and particles in the air, with some studies claiming that they help reduce local concentrations of nitrogen oxide by up to 57%.

树木还可以减少废气和空气中颗粒的数量，一些研究声称，它们有助于将当地的氮氧化物浓度降低高达 57%。