AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Quantifying the Contribution of Primary and Secondary Emissions to Ultrafine Particle Contributions in the United States with the Regional Chemical Transport Model
BENJAMIN MURPHY, Francis Binkowski, Ekbordin Winijkul, Tinja Olenius, Ilona Riipinen, Matthew Alvarado, Matthew Woody, Havala Pye, United States Environmental Protection Agency
Abstract Number: 551 Working Group: Regional and Global Air Quality and Climate Modeling
Abstract Both direct particle emissions and secondary formation and growth from vapor precursors are responsible for increasing ultrafine particle (UFP) concentrations and have impacts on aerosol properties (e.g. bulk surface area). We have updated the Community Multiscale Air Quality (CMAQ) model with new algorithms and data to investigate the contributions of gaseous and particulate sources to UFP concentrations throughout the US.
In a traditional model, new particle formation (NPF) events rely principally on sulfuric acid, charged ions and, more recently, a stabilizing molecule (e.g. NH3, amine, etc) to begin. However, evidence shows that organic compounds are capable of participating with sulfuric acid or, when sulfuric acid concentrations are low, forming particles on their own. Moreover, organic vapors drive the growth of particles to larger sizes in many environments. The new aerosol processing module in CMAQ is designed for robust prediction of particle number sources, sinks, and concentrations, while leveraging the speed and flexibility of modal aerosol techniques, and including state-of-the-art schemes for treating new particle formation (e.g. Atmospheric Cluster Dynamics Code). We have also updated the parameterization of aerosol emissions from a single-distribution approach to a rich dataset of multiple distributions with dependencies on emission source, technology, and fuel.
We apply the new model to observations made throughout the US including California, the mountain west, the southeast US and the northeast US. This combination of sites allows us to characterize the model in urban, suburban, and rural locations, among which the drivers of UFP concentrations are expected to change dramatically. We then quantify the spatio-temporal variation in the contribution of primary/secondary sources to particle number and surface area, two metrics thought to be important for connecting particulate pollution to human health impacts. This exercise improves our understanding of the most effective ways to mitigate the highest UFP concentrations in the US.