Date of Award

8-2009

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Atmospheric Studies

Abstract

Asian dust events during INTEX-B were analyzed by using chemical and physical in situ measurements taken by instruments on board a NASA DC-8 aircraft during the INTEX-B (2006) field campaign. From this analysis, the three following scientific questions about the nature of the Asian dust events were answered: (1) How can we identify which mode dominates in the observed dust plumes, (2) How do the pollutants and Asian dust interact with eac': other to form secondary pollutants, and (3) Has the pollution measured over the remote Pacific increased over the time interval of two previous field experiments (PEM-B 1994 and TRACE-P 2001) that conducted research of Asian dust and pollution over the western remote Pacific.

For the first question, DIAL measurements at 588 and 1064 nm can roughly define the dust/pollution plume boundary. The magnitude of wavelength dependence of the aerosol scattering ratios at 450, 550 and 700 nm as measured by the nephelometer demonstrates whether the plume contains fine mode aerosols; which is believed to be an excellent indicator of whether the Asian dust plume is carrying any pollution along its transport pathway. Based on the wavelength dependence, three types of Asian dust plumes were identified: (a) Type I - a plume dominated by coarse mode aerosol, which is weakly dependent on wavelength (dust), (b) Type II - a plume dominated by fine mode aerosol, which is strongly dependent on wavelength (pollution), and (c) Type III - two plumes that contained a mixture of both Asian dust and pollution.

A HYSPLIT backward trajectory model was used to verily the origins of these dust plumes as crossing through desert regions, regions of large urban populations, as well as mixtures of both. Chemical data derived from ion and gas chromatography was used to show the tracers of dust (calcium ions), aqueous phase pollution (sulfate and nitrate ions) and gas phase pollution (sulfur dioxide).

The second question focused on gas to particulate phase reactions (tine mode to coarse mode pollution conversions) and used the same four plume cases as the first question. Types I and II had 16 and 18 pptv sulfur dioxide, respectively, while Type III had 78 and 93 pptv, respectively. Both the strong dust and strong pollution cases showed a more complete conversion where the two mixture cases suggested incomplete gas to particulate phase reactions at the point where the aircraft intercepted the plume. To answer the third question, a technique adopted by Dibb et al. (1996, 1997, and 2003) was used to show whether pollution has increased over the three field campaigns. Though the data shows an inherent increase, there is no conclusive evidence for a possible pollution increase since no observations from the source regions exist for the purpose of this study. Therefore, the observed increased trends may be due to better sampling techniques and methods developed for the INTEX-B 2006 field campaign.

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