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Two-year-long high-time-resolution apportionment of primary and secondary carbonaceous aerosols 

in the Los Angeles Basin using an advanced total carbon–black carbon (TC-BC(λ)) method 

Abstract 

In recent years, carbonaceous aerosols (CA) have been recognized as a significant contributor to the concentration of
particles smaller than 2.5 μm(i.e., PM2.5), with a negative impact on public health and Earth's radiative balance. In this
study, we present a method for CA apportionment based on high-time-resolution measurements of total carbon (TC),
black carbon (BC), and spectral dependence of absorption coefficient using a recently developed Carbonaceous Aerosol
Speciation System (CASS). Two-year-long CA measurements at two different locations within California's Los Angeles Basin 

are presented. CA was apportioned based on its optical absorption properties, organic or elemental carbon composition,

and primary or secondary origin.We found that the secondary organic aerosols (SOA), on average, represent >50%of 

CA in the study area, presumably resulting from the oxidation of anthropogenic and biogenic volatile organic components. 

Remarkable peaks of SOA in summer afternoons were observed, with a fractional contribution of up to 90 %. On the other

hand, the peak of primary emitted CA, consisting of BC and primary organic aerosol (POA), contributed >80 % to the CA

during morning rush hours on winter working days. The light absorption of BC dominated over the brown carbon (BrC),

which contributed to 20 % and 10 % of optical absorption at the lower wavelength of 370 nm during winter nights and

summer afternoons, respectively. The highest contribution of BrC, up to 50 %, was observed during the wildfire periods.

Although the uncertainty levels can be high for some CA components (such as split between primary emitted and 

secondary formed BrC during winter nights), further research focused on the optical properties of CA at different locations

may help to better constrain the parameters used in CA.   

Key words 

Brown carbon, Primary organic aerosol, Secondary organic aerosol, Aethalometer, Total carbon analyzer, Carbonaceous aerosol speciation system

▶Sources : Science of Total Environment 848 (2022) 157606