It's funny how we become more and more specialized in a field, learing all kinds of details about one little niche, while we can be completely ignorant of other parts of the field. Then you have to wonder about defining a field and subfields and such, but anyway that was just a comment meant to lead into this story. I really don't know very much about air pollution, from the chemical and health sides of the story. Yeah, greenhouse gases or water vapor and I can keep up, but volatile organic compounds and I struggle more than I'd like. Related to a mother's day conversation I had this weekend, I happened upon a story about air pollution due to dairies in California [LINK]. It seems that California somehow classifies the waste produced by cows according to a study conducted in 1938, and now they are trying to decide how to update their classification.
First off, I don't doubt that people could measure cow waste in 1938. It probably isn't that difficult to do. Of course, there might be differences in what you measure, and methods of measuring, but I wouldn't be too surprised if modern techniques gave approximately the same answer for some "control cow." However, I have a strong feeling that today's dairy cows are demonstrably different from those in 1938. Today, dairy cows are raised and used for just a few years before being shipped off to become hamburger or dog food or whatever. These cows don't live like normal cows. They don't wake up each morning, eat some grass, and eventually get milked by some farm hand. They are attached to automatic milking machines, they are forced to continuously produce milk until their production decreases below some threshold, and who knows what kinds of, let's just say medicine, they are given. So, yeah, it is probably nigh time to update that classification.
The article mentions three distinct numbers, ranging from about 6 pounds of waste per year per cow to about 38 pounds per cow per year. This isn't total waste, obviously; if you've ever spent time around cows you'll know they produce about 6 pounds of waste per day, and maybe more. These numbers try to measure the effect on air quality. So that would include the gas cows expel, and some fraction of their solid waste that might end up in the air. I have no clue how they try to measure that, but the range of estimates suggests there is disagreement about how it should be done. The article makes certain to suggest these numbers are "politicized," with environmentalists (whoever they are) favoring the larger number and the dairy industry (or some lawyers who work for some big agri-business) favoring the smaller number.
An interesting tidbit is that the San Joaquin Valley has terrible air quality, and the dairy industry is a giant polluter locally. You can confirm the bad air quality by looking it up, which I did this weekend while investigating a different matter. If the dairies can be shown to be culpable for the pollution, it would be a great step forward to regulate their waste in a more reasonable way. After all, there weren't always 2-million cows being stored in the SJV.