20 research outputs found
Impacts of Traffic Reductions Associated With COVID-19 on Southern California Air Quality
On 19 March 2020, California put in place Stay‐At‐Home orders to reduce the spread of SARS‐CoV‐2. As a result, decreases up to 50% in traffic occurred across the South Coast Air Basin (SoCAB). We report that, compared to the 19 March to 30 June period of the last 5 years, the 2020 concentrations of PM_(2.5) and NO_x showed an overall reduction across the basin. O₃ concentrations decreased in the western part of the basin and generally increased in the downwind areas. The NO_x decline in 2020 (approximately 27% basin‐wide) is in addition to ongoing declines over the last two decades (on average 4% less than the −6.8% per year afternoon NO₂ concentration decrease) and provides insight into how air quality may respond over the next few years of continued vehicular reductions. The modest changes in O₃ suggests additional mitigation will be necessary to comply with air quality standards
Source apportionment of ambient particle number concentrations in central Los Angeles using positive matrix factorization (PMF)
In this study, the positive matrix factorization (PMF) receptor model
(version 5.0) was used to identify and quantify major sources contributing
to particulate matter (PM) number concentrations, using PM number size
distributions in the range of 13 nm to 10 µm combined with several
auxiliary variables, including black carbon (BC), elemental and organic
carbon (EC/OC), PM mass concentrations, gaseous pollutants, meteorological,
and traffic counts data, collected for about 9 months between August 2014
and 2015 in central Los Angeles, CA. Several parameters, including particle
number and volume size distribution profiles, profiles of auxiliary
variables, contributions of different factors in different seasons to the
total number concentrations, diurnal variations of each of the resolved
factors in the cold and warm phases, weekday/weekend analysis for each of
the resolved factors, and correlation between auxiliary variables and the
relative contribution of each of the resolved factors, were used to identify
PM sources. A six-factor solution was identified as the optimum for the
aforementioned input data. The resolved factors comprised nucleation,
traffic 1, traffic 2 (with a larger mode diameter than traffic 1 factor),
urban background aerosol, secondary aerosol, and soil/road dust. Traffic
sources (1 and 2) were the major contributor to PM number concentrations,
collectively making up to above 60 % (60.8–68.4 %) of the total number
concentrations during the study period. Their contribution was also
significantly higher in the cold phase compared to the warm phase.
Nucleation was another major factor significantly contributing to the total
number concentrations (an overall contribution of 17 %, ranging from
11.7 to 24 %), with a larger contribution during the warm phase than
in the cold phase. The other identified factors were urban background
aerosol, secondary aerosol, and soil/road dust, with relative contributions
of approximately 12 % (7.4–17.1), 2.1 % (1.5–2.5 %), and 1.1 %
(0.2–6.3 %), respectively, overall accounting for about 15 %
(15.2–19.8 %) of PM number concentrations. As expected, PM number
concentrations were dominated by factors with smaller mode diameters, such
as traffic and nucleation. On the other hand, PM volume and mass
concentrations in the study area were mostly affected by sources with
larger mode diameters, including secondary aerosols and soil/road dust.
Results from the present study can be used as input parameters in future
epidemiological studies to link PM sources to adverse health effects as well
as by policymakers to set targeted and more protective emission standards
for PM
Spatial and temporal variability of sources of ambient fine particular matter (PM<sub>2.5</sub>) in California
International audienceCE 27 oct. 2011, Association Analyser, n° 341278, au Lebon ; AJDA 2011. 209
Spatial and temporal variability of sources of ambient fine particulate matter (PM<sub>2.5</sub>) in California
To identify major sources of ambient fine particulate matter (PM2.5, dp < 2.5 μm) and quantify their contributions
in the state of California, a positive matrix factorization (PMF) receptor
model was applied on Speciation Trends Network (STN) data, collected between
2002 and 2007 at eight distinct sampling locations, including El Cajon,
Rubidoux, Los Angeles, Simi Valley, Bakersfield, Fresno, San Jose, and
Sacramento. Between five to nine sources of fine PM were identified at each
sampling site, several of which were common among multiple locations.
Secondary aerosols, including secondary ammonium nitrate and ammonium
sulfate, were the most abundant contributor to ambient PM2.5 mass at
all sampling sites, except for San Jose, with an annual average cumulative
contribution of 26 to 63%, across the state. On an annual average basis,
vehicular emissions (including both diesel and gasoline vehicles) were the
largest primary source of fine PM at all sampling sites in southern
California (17–18% of total mass), whereas in Fresno and San Jose,
biomass burning was the most dominant primary contributor to ambient
PM2.5 (27 and 35% of total mass, respectively), in general
agreement with the results of previous source apportionment studies in
California. In Bakersfield and Sacramento, vehicular emissions and biomass
burning displayed relatively equal annual contributions to ambient
PM2.5 mass (12 and 25%, respectively). Other commonly identified
sources at all sites included aged and fresh sea salt and soil, which
contributed to 0.5–13%, 2–27%, and 1–19% of the total mass,
respectively, across all sites and seasons. In addition, a few minor sources
were identified exclusively at some of the sites (e.g., chlorine sources,
sulfate-bearing road dust, and different types of industrial emissions).
These sources overall accounted for a small fraction of the total PM mass
across the sampling locations (1 to 15%, on an annual average basis)