According to Adrian Martinez, lawyer for NRDC:
To make up for the lack of credits EPA found to be invalid, the District is now seeking to go back in time to collect reductions in pollution that had previously been a benefit to the air, but will now be administered to allow more pollution. In some cases, the District is proposing they can collect on clean air gains that happened nearly 20 years ago, in an effort to dole out those clean up credits now.
If you wonder how L.A. is still Number One is ozone pollution, look no further than our own regulatory backyard.
Mr. Martinez offers more on his NRDC blog.