Abstract Number: 637 Working Group: Instrumentation and Methods
Abstract Four complementary techniques were used to measure the organic composition of generated and ambient marine aerosol collected during the Western Atlantic Climate Study (WACS) in August 2012. Particles were generated using a model ocean system, the Sea Sweep, and compared to ambient particles. The four techniques used are: (i) Fourier transform infrared (FTIR) spectroscopy which gives organic functional group composition of particles collected on filters; (ii) high resolution time of flight aerosol mass spectrometry (HR-ToF-AMS) that determines the non-refractory mass spectral composition of particles; (iii) light scattering (LS) module of the HR-ToF-AMS (LS-ToF-AMS) that determines single particle mass spectral composition; and (iv) scanning transmission X-ray microscopy with near-edge X-ray absorption fine structure (STXM-NEXAFS) that measures the morphology and organic functional group composition of single particles. The organic mass of marine particles was split into organics with high ratios of oxygen to carbon (O/C), such as hydroxyl functional groups, and those with low O/C, such as alkane functional groups. Using this, the ambient composition compares well across all four techniques with all showing about 50% of the organic mass could have a high O/C. LS-ToF-AMS was used to determine the apparent collection efficiency (CE) of the AMS by comparing the number of particles that both scattered light and had a significant mass spectrum to those that only scattered light. For ambient, this CE was about 50%, consistent with past values. For the generated particles, less than 10% of those detected by light scattering also had associated mass spectra, suggesting that more than 90% were refractory. This is consistent with the fact that more than 80% of the generated submicron particle mass is attributed to sea salt, which is refractory. STXM-NEXAFS measurements show that Sea Sweep particles contain high O/C organics on sea salt, which are refractory and not vaporized by AMS.