posted on 2021-03-04, 21:32authored byClara
M. Nussbaumer, Ronald C. Cohen
Air quality policy in the Los Angeles
megacity is a guidepost for
other megacities. Over the last 2 decades, the policy has substantially
reduced aerosol (OA) concentrations and the frequency of high aerosol
events in the region. During this time, the emissions contributing
to, and the temperature associated with, high aerosol events have
changed. Early in the record, aerosol concentrations responded to
a variety of different sources. We show that emission control has
been effective with a strong decrease in temperature-independent sources.
As a result, the response of aerosol to temperature has become a dominant
feature of high aerosol events in the basin. The organic fraction
of the aerosol (OA) increases with the temperature approaching 35%
at 40 °C. We describe a simple conceptual model of aerosol in
Los Angeles, illustrating how benzene, toluene, ethylbenzene, and
xylenes (BTEX) and isoprene, along with molecules for which these
are plausible surrogates such as monoterpenes, are sufficient to explain
the observed temperature dependence of PM 2.5.