The Bay Area Air Quality Management District has issued a second Spare the Air alert in a row for today because it expects the air quality will be poor like it was yesterday.
The alert does not mean free transit rides. The alert means the air will be particularly stale and hot again, meaning children and seniors especially will be more susceptible to harmful pollutants.
Motor vehicle exhaust, gasoline vapors, industrial emissions and household chemicals all contain volatile, organic compounds and nitrogen oxides that combine with oxygen in heat and sunlight to form a ground-level ozone.
This is the fourth alert of the season.
Anyone with respiratory or heart problems should try to stay inside.
Simple things such as walking instead of driving, avoiding the use of aerosol spray and cooking inside instead of on a barbecue can help make the air less harmful.