AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Long-Term Trends in Chemical Composition of PM2.5 in the South Coast Air Basin: A Focus on Time-integrated and Continuous Carbon Measurements
FARAZ ENAYATI AHANGAR, Sina Hasheminassab, Payam Pakbin, Andrea Polidori, Aaron Katzenstein, Jason Low, South Coast Air Quality Management District
Abstract Number: 736 Working Group: Carbonaceous Aerosol
Abstract Implementation of stringent regulations on stationary and mobile sources at the local, state, and federal levels over the past two decades has resulted in a substantial reduction of ambient PM2.5 concentrations in the South Coast Air Basin (SCAB). This study quantifies the trends in total mass and chemical constituents of ambient PM2.5 concentration for the period of 2004 to 2018, utilizing long-term measurements at routine monitoring stations in urban and rural areas of the SCAB. The main focus of this study is the carbonaceous species in PM2.5 (i.e., elemental/black and organic carbon (EC, BC, OC, respectively)).
Since diesel PM (DPM) cannot be measured directly, EC is generally used as a surrogate to estimate diesel PM. The regulatory efforts to reduce diesel emissions has resulted in significant reductions in EC emissions from the diesel fleet in the SCAB. Thus, time-integrated EC may no longer be a suitable tracer for estimating the health impacts of diesel emissions as well as assessing the relative impacts of diesel emissions and biomass burning (e.g. wildfires and residential wood combustion) on local and regional air quality and will require further investigation. This is particularly important for apportioning the impacts of short-lived air quality events such as wildfires which can fluctuate significantly across years. The light-absorbing carbon content of PM can be measured with much higher time resolution using optical methods (operationally defined as BC) and address this issue. In this study, we investigated the relationship between time-resolved BC (measured by Aethalometer AE33) and time-integrated thermal EC at different locations between 2012 and 2018. This study highlights the advantage of having high time-resolution measurements in localized air quality monitoring as well as long-term trend assessments.