Study: Los Angeles Air a Lot Cleaner, in One Respect

The amount of one particular class of smog-forming chemicals in Los Angeles' air has dropped by a surprising amount, according to a study published yesterday in the Journal of Geophysical Research. The concentration of volatile organic compounds (VOCs), an important component in the creation of smog, has dropped by approximately 98% in the L.A. Basin's airshed over the last half-century, from 100 parts per billion (ppb) in 1960 to 2ppb in 2010.

VOCs are a major contributor to ground-level ozone, a serious health hazard that can cause or worsen asthma and other respiratory ailments, as well as damaging the vegetation in forests and deserts downwind.

Most VOCs in L.A.'s air get there by way of automobile tailpipes, and the researchers who published the study credit improvements in auto technology for the steady improvement. "The reason is simple: Cars are getting cleaner," said the study's lead author Carsten Warneke, Ph.D., of the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder.

Warneke et al's research, funded in large part by the National Oceanic and Atmospheric Administration (NOAA), found that since 1960 the concentration of VOCs has dropped by an average of 7.5% per year over the five-decade period since. What makes the decline even more surprising is that over the same period, gasoline use in the area has nearly tripled. In 1960, Angelenos consumed somewhere in the neighborhood of 137 million barrels of gasoline: in 2010, that figure was around 364 million barrels.

If measured chemical-by-chemical rather than totalling VOCs as a group, the data show not all VOCs are dropping. Ethane and propane, whose sources are mainly non-automotive, have declined less dramatically; ethanol, increasingly used as a fuel additive, has actually increased in atmospheric concentration. Still, Warnecke says he expects the decline in VOCs to continue due to new, more efficient vehicles and the retirement of aging clunkers.

Angelenos who've been here since the 1960s will remember well when you often couldn't see the Hollywood Hills from Wilshire (see L.A.'s Smoggy Past, in Photos). If the trends Warnecke and his colleagues describe continue, smoggy days like those may increasingly be relegated to the past.