Source apportionment of carbonaceous aerosol in different regions of the world.

摘要

To improve the understanding of carbonaceous aerosol sources, methods for source apportionment were developed, applied, and assessed in diverse atmospheres worldwide. Locations of study ranged from polluted megacities to rural locations in South Asia, central Mexico, and the United States. Apportionment focused on organic and elemental carbon (OC and EC), of interest for its contributions to ambient aerosol mass and impacts on radiative and climate forcing. Advances in source apportionment via this work include the ability (i) to focus on climate-relevant aerosol components, (ii) to function in a wide-range of geographic locations, (iii) to gain information about sources in need of further characterization, and (iv) to distinguish between primary and secondary sources.For heavily urbanized megacities, like Mexico City and Lahore, Pakistan, the chemical mass balance (CMB) modeling approach to source apportionment was adequate in accounting for the majority of primary organic aerosol. In the South Asian regional haze impacting Maldives high EC levels were the focus of source apportionment. Sources of EC were evaluated using multi-variant positive matrix factorization (PMF) based on trace metal species. To assess the role of biofuel contributors at atmospheric EC, source profiles were developed for biofuel burning in residential stoves widely-used in South Asia. These profiles were applied in a source apportionment sensitivity study carbonaceous aerosol in the foothills of the Kathmandu Valley.Estimates of secondary organic aerosol (SOA) contributions to ambient aerosol were enhanced by the development of two methods. The first method estimated SOA as the water-soluble OC not apportioned to primary sources by CMB modeling. The second method incorporated SOA tracer species into CMB modeling using tracer-to-OC ratios drawn from the literature. Comparison of SOA composition and sources across different air sheds revealed striking differences, indicating that secondary precursors and formation mechanisms varied by region. Spatial differences in carbonaceous aerosol sources were used in conjunction with new chemical characterization techniques to elucidate the origins of high-molecular weight organic aerosols and humic-like substances (HULIS) detected using liquid-chromatography tandem mass spectrometry. Throughout this work, various approaches to source apportionment were assessed for their utility and comprehensiveness in different parts of the world.