Abstract View
High Time-Resolution Measurement of Carbonaceous Aerosol in Central Los Angeles With New TC-BC Method
MARTIN RIGLER, Matic Ivančič, Gašper Lavrič, Sina Hasheminassab, Payam Pakbin, Tony Hansen, Aerosol d.o.o.
Abstract Number: 355
Working Group: Carbonaceous Aerosol
Abstract
Measurements of carbonaceous aerosols are of vital importance for local, regional, and global air quality monitoring. Because of their diverse physical and chemical properties, they directly impact air quality, visibility, cloud nucleation and cloud optical properties, the planetary radiation balance, and public health. The amount of carbon found in carbonaceous aerosols is called total carbon (TC), which is commonly categorized into fractions of organic carbon (OC) and elemental carbon (EC). Particulate OC can be directly emitted to the atmosphere (i.e., primary OC) or can be formed in the atmosphere from gas-to-particle conversion of (semi)volatile organic compounds after oxidation and condensation/nucleation (i.e., secondary OC). The chemical and physical processes associated with secondary organic aerosols (SOA) formation are complex and, therefore, represents a major research challenge in atmospheric science. Highly time-resolved SOA measurement techniques are required to evaluate its impact on atmospheric processes, climate and human health (Hallquist et al., 2009).
Newly developed online TC-BC method (Rigler et al., 2019), which combines an optical method for measuring mass equivalent black carbon (eBC) by the AE33 Aethalometer (Drinovec et al., 2015; Hansen et al., 1984), and a thermal method for total carbon (TC) determination by the Total Carbon Analyzer TCA08 was used for this study. The TC-BC method determines equivalent organic carbon (eOC) fraction of carbonaceous aerosols defined as eOC = TC – eEC, where eEC = b·eBC is equivalent to elemental carbon and the determined proportionality parameter b is a slope of regression analysis between EC and eBC.
In collaboration with the South Coast Air Quality Management District, an air monitoring campaign was conducted at an air monitoring station in central Los Angeles from March 2018 to December 2019. In this study, TCA08 and AE33 were used on 1h time resolution. eOC and eEC results were compared to 24h filter-based carbon measurements (sampled every third day) and other PM and meteorological parameters. In this study the diurnal patterns for eEC and eOC concentrations are compared for different seasons. Both eEC and eOC exhibit considerable daily, monthly and seasonal variations. The effect of morning rush hour peak in eEC is particularly pronounced in colder months, when higher traffic density is coupled with shallower mixing height. During warmer months eOC concentrations exhibit mid-day peak, which is associated with generation of secondary OC through photochemical processes in the atmosphere. Less pronounced peak of eEC in the evening is mostly caused by evening rush hour and a lower mixing height.