In Shell Oil's defense, "Wednesday's gas giveaway was part of a nationwide event planned weeks in advance". The same could not be said of the "Spare the Air" day - which was alerted to the Bay Area called by the regional Air District via various media alerts (including personal emails to anyone who subscribes for the alerts) on Tuesday.
The Air District advises that "if motorists must drive on Spare the Air Days, they're encouraged to carpool with other commuters. And if they plan on filling up their gas tank, the evening is the least harmful time to do so."
The give-away was done in the morning - allowing all those vehicle emissions from the long queue of idling vehicles to contribute to the day's ozone build-up. The Bay Area has experienced 4 days where it exceeded the federal 8-hour ozone standard this year.
Several years ago, a far better give-away was deliberately offered when a 'Spare the Air' alert was called: free public transit.
Thanks to California League of Conservation Voters