Molecular Chemistry of Nitrogen-Containing Light-Absorbing Compounds in Atmospheric Organic Aerosol
EMSL Project ID
44657
Abstract
Most atmospheric aerosols scatter visible radiation back to space and therefore reduce the amount of solar energy reaching the surface. However, certain types of aerosols absorb visible radiation and lead to local heating in areas where such aerosols are prevalent. More recent measurements have shown that "brown" light-absorbing organic aerosols are widespread in urban and rural environments and may in fact dominate the total aerosol absorption in certain areas. The goal of this proposal is to investigate a new mechanism of formation of "brown carbon" compounds from secondary organic aerosols (SOA), and characterize the relevant chromophores using a combination of field observations and laboratory measurements. Recent experiments at UCI and PNNL have revealed a new potentially important source of "brown carbon" compounds. Specifically, we have relied on methods of high-resolution mass spectrometry (HRMS) to demonstrate that reactions between carbonyl compounds in biogenic SOA and reduced nitrogen compounds such as ammonia and amino acids produce light-absorbing compounds on atmospherically relevant time scales. The most important chromophores are extensively conjugated N-heteroatom species, which appear to be similar in structure to compounds produced by browning of heated foods. In a parallel effort, the Yang group have examined the composition of particulate matter in Shanghai with Aerosol Time-of-Flight Mass Spectrometry (ATOFMS).These measurements have found nitrogen containing compounds, which were consistent with the carbonyl + NH3 chemistry. These types of compounds appear to be widespread in aerosols but their molecular identities remain ill-defined. The proposed research will utilize high resolution mass spectrometry at EMSL coupled with LC separation stage and a photodiode array (PDA) UV/Vis light absorption detector for detailed analysis of light-absorbing N-heteroatom organics in aerosols. For broader scope, our research program will establish unique basis for closure studies aimed to reduce the uncertainty associated with the climatic effects of light-absorbing OA. Specific tasks of the proposed work include: LC-UV/VIS detection and high resolution MS-(MSn) analysis of specific chromophores; investigation of the relationship between the molecular composition and light-absorbing properties of the chromophores; analysis of OA collected in laboratory and field studies aiming to improve our understanding of the "brown carbon" chemistry, mechanisms of its formation and atmospheric evolution. We propose a collaborative investigation of the mechanism of formation of light-absorbing N-containing compounds in aerosols. We plan to conduct the following types of experiments: - Collection of aerosol samples in Shanghai, China on days characterized by increased NH3 concentrations and increased SOA concentrations, the conditions favoring the carbonyl+ NH3 chemistry. (Fudan group).
- Laboratory investigation of the SOA aging processes leading to the formation of similar compounds from photooxidation of model anthropogenic and biogenic precursors in presence of ammonium sulfate. (UCI group).
- Characterization of the optical properties and molecular composition of the collected samples with the LC-UVVIS-HRMS analytical platform at EMSL to identify the formulas and likely structures of the relevant chromophores (PNNL group).
Project Details
Project type
Large-Scale EMSL Research
Start Date
2011-10-01
End Date
2012-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Nguyen TB, S Nizkorodov, A Laskin, and J Laskin. 2013. "An approach toward quantification of organic compounds in complex environmental samples using high-resolution electrospray ionization mass spectrometry." Analytical Methods 5(1):72-80. doi:10.1039/c2ay25682g