However, independent studies by Professor Frank Mitloehner, an air quality specialist at the University of California, Davis, threw into question the air board’s plans. Mitloehner showed that cow manure produces less VOCs than was previously thought, and that a major source from dairies wasn’t manure, but rotting feed in storage facilities on the farms. It was also found that VOCs from cow manure were already being broken down in dairy waste ponds, and that a low-cost way of dealing with VOCs produced by cow waste is simply to use water to flush out manure to those ponds. Installing digesters would have been an expensive and ineffective option.

“But before that, there was going to be this mandate … that was going to cost farmers millions, that wouldn’t have done anything to mitigate these emissions,” Marsh said, referring to the proposed methane digester rule. The air board ultimately relented on pursuing that requirement.

But there was an even bigger problem with the air district’s science. Mitloehner said research showed that even the elimination of Volatile Organic Compounds from dairy farms would likely have little impact on smog formation in San Joaquin, because VOCs are also produced in large quantities naturally. Rather, pursuing stepped up regulation of nitrous oxides (NOx) emissions, a type of smog-forming pollutant produced mainly by human activity, offered the agency the best chance of mitigating air contamination, he said. Ironically, NOx are produced in significant quantities by digesters.

The California dairy industry’s experience with methane digesters also provides an example of the problematic conflicts that arise between state environmental agencies pursuing different objectives. Although digesters would have been ineffective at reducing VOCs in San Joaquin, statewide the technology is seen by some environmentalists as a promising tool for combating greenhouse gas emissions, as they can be used not only to eliminate methane, a particularly virulent greenhouse gas, but also to produce renewable energy, by burning the gas in generators to produce electricity. CARB, which is responsible for implementing AB 32, the California Global Warming Solutions Act, has promoted digesters as a means of mitigating emissions.

But dairies that have taken the lead in voluntarily installing costly digesters to reduce their emissions and test the economic viability of the technology have met with hurdles posed by local air quality district regulations, which are now concerned with controlling NOx emissions. Some have ceased operating their digesters as a result.

Ron Koetsier, a dairy farmer in Tulare County in the state’s Central Valley Area, said he decided to shut his digester down permanently in July 2008 when the San Joaquin air district came up with a rule that required dairies make expensive modifications to their digester equipment, such as installing catalytic converters on generators. The rule went into effect in 2009.

“When that rule came out from the air board, we had to shut it off,” Koetsier said. “I wasn’t about to spend another $150,000 for something that wasn’t going to pencil out any more anyway.”