The US Environment Protection Agency (EPA) has backed plans to improve air quality in parts of San Francisco.
Officials want to take action to reduce the amount of PM2.5 particles that are airborne across the South Coast and throughout San Joaquin Valley.
Air monitoring results have suggested that these regions are the worst affected by this type of pollutant because of emissions released by ship traffic and trucks.
However, there have been improvements in the past decade, with a 14 per cent reduction in particulate matter seen in San Joaquin Valley and a 43 per cent decline reported along the South Coast.
EPA regional administrator for the Pacific south-west Jared Blumenfeld said clean air is vital to people's health.
"These air quality plans rely on first-of-their kind requirements for the engines in trucks, ships and construction equipment, impacting almost a million vehicles in California," he commented.
Last week, the EPA revealed it would remove 1.4 million tonnes of soil that was contaminated by radium and uranium at the Northeast Church Rock Mine in San Francisco.
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