AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Spatially and Seasonally Resolved Estimate of the Global Organic Matter to Organic Carbon Ratio Inferred from Aerosol Mass Spectrometer Measurements and Satellite-Derived Ground-Level Nitrogen Dioxide Concentrations
Abstract Number: 211 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Particulate organic matter (OM) is of intense interest for air quality and climate research, but the relationship between OM and organic carbon (OC) remains poorly constrained. We present a novel method to estimate the spatially and seasonally resolved global OM/OC ratio. First, we develop a parameterization for the OM/OC ratio using the hydrocarbon-like organic aerosol (HOA) fraction of total OM measured globally with the Aerosol Mass Spectrometer (AMS). Second, we use ground-level NO$_2 concentrations derived from the Ozone Monitoring Instrument (OMI) satellite sensor to serve as a proxy for fresh emissions that have a high HOA fraction. The combination of these two methods yields predictions of OM/OC from NO$_2 measurements. We use two-thirds of a database of AMS field measurements (47 observations) to formulate a prediction model of the OM/OC ratio; evaluation of the full NO$_2 --> OM/OC relationship with the remaining data yields significant agreement (r = 0.76, slope = 0.96, n = 21). The global OM/OC ratio ranges from 1.3 to 1.9 (micro-gram/micro-gram Carbon), with distinct spatial variation that clearly reflects the difference between urban and rural regions. The seasonal OM/OC ratio has a summer maximum and a winter minimum over regions dominated by high combustion emissions. This parameterization could be included into models for estimating the OM/OC ratio using the simulated NO$_x or NO$_2 concentrations.