The air quality Californians are enjoying during the stay-at-home order could one day be the status quo, if the state follows the instructions of a UCLA study.  The study, published in the journal Nature Sustainability, offers a road map to state and local policymakers for California to use existing policies and technologies to drastically decrease greenhouse gas emissions and air pollution by 2050, according to Yifang Zhu, one of the study’s lead authors and a professor at the UCLA Fielding School of Public Health and Institute of Environment and Sustainability.