But variables like pedestrians in crosswalks, large crowds and vehicle wrecks can throw a carefully designed system out of whack, leading to annoying and pollution-causing traffic jams.

但是，正在穿越人行横道的路人、摩肩接踵的人群以及道路上抛锚的事故车等不确定因素都可能让一套精心设计的系统崩溃失常，导致恼人而又产生污染的交通拥堵。

youdao

In January 1994 an oil barge ran aground off the coast of San Juan, Puerto Rico, leaking its cargo of 750000 gallons into the ocean while causing the pollution of the city's beaches.

1994年1月，一艘油驳船在波多黎各圣胡安海岸触礁，将75万加仑的货物泄漏到海洋中，并污染了该市的海滩。

youdao

Under inversion and other weather conditions, haze is a form of urban and regional pollution, causing by aerosol.

霾在大气逆温等稳定气象条件下，由气溶胶和气体污染物造成的一种城市和区域性空气污染现象。

youdao

But when it comes to reducing pollution-causing emissions, electric vehicles have a lot of competition from cars powered by natural gas.

CNN: Natural gas vehicles on a roll in U.S.

The EPA last year issued the first-ever standards to control smog- and soot-forming gases from gas wells site, and updated existing rules to reduce cancer-causing pollution, such as benzene, from other equipment.

NPR: Report: Flaws In EPA Drilling Pollution Data

Opponents warn that fracking is an environmental disaster waiting to happen, citing, among other risks, air and water pollution, the release of radiation and cancer-causing substances, and the acceleration of global climate change as methane and other greenhouse gases escape during fracking.

FORBES: Fracking: A Role for Universities