Determination of chemical species in individual aerosol particles using ultrathin window EPMA

The determination of low-Z elements such as carbon, nitrogen, and oxygen in individual atmospheric aerosol particles is of interest in studying enviro nmental pollution. By the application of a newly developed EPMA technique, which employs either windowless or thin-window EDX detector, chemical compo sitions, including the low-Z components, of individual particles can quanti tatively be elucidated. The determination of low-Z elements in individual e nvironmental particles allows to improve the applicability of the single pa rticle analysis; many environmentally important atmospheric particles, e.g. sulfates, nitrates, ammonium, and carbonaceous particles, contain low-Z el ements, which cannot be characterized using conventional energy dispersive- EPMA (ED-EPMA). Furthermore, the diversity and the complicated heterogeneit y of atmospheric particles in chemical compositions can be investigated in details, using the new EPMA technique. This work demonstrates that the quan titative determination of chemical species in individual particles is possi ble using ultrathin window EPMA coupled with Monte Carlo based quantificati on. Using the new EPMA method, molar concentrations of major chemical speci es in individual environmental particles can be determined. For example, th e molecular concentrations of ammonium sulfate and nitrate in single partic le were analyzed for particles internally mixed with ammonium sulfate and n itrate species. When particles are composed of several chemical species so that the number of equations is smaller than the number of chemical species to be determined, the quantitative analysis of each chemical species can b e ambiguous; however, many particles are composed of one or two major chemi cal species, and thus this technique could provide direct observation of at mospheric chemistry for airborne particles in more detail.