Trans-Pacific dust events observed at Whistler, British Columbia during INTEX-B

I G Mckendry,A M Macdonald,W R Leaitch,Q Zhang,A Van Donkelaar,R V Martin,T Duck

doi:10.5194/acp-8-6297-2008

Abstract

Abstract. The meteorology and physico-chemical characteristics of aerosol associated with two new cases of long range dust transport affecting western Canada during spring 2006 are described. Each event showed enhancements of both sulfate aerosol and crustal material of Asian origin. However, the events were of quite different character and demonstrate the highly variable nature of such events. The April event was a significant dust event with considerable enhancement of fine particle sulfate while the May event was a weaker dust event, also with significant fine particle sulfate enhancement. The latter event was notable in the sense that it was of short duration and was quickly followed by a large increase of organic material likely of regional origin. Comparison of these two events with other documented cases extending back to 1993, suggests that all dust events show coincident enhancements of sulfate and crustal aerosol. However, events vary across a wide continuum based on the magnitude of aerosol enhancements and their sulfate to calcium ratios. At one extreme, events are dominated by highly significant crustal enhancements (e.g. the well-documented 1998 and 2001 "dust" events) while at the other are events with some dust transport, but where sulfate enhancements are of very high magnitude (e.g. the 1993 event at Crater Lake and the 15 May 2006 event at Whistler). Other events represent a "mix". It is likely that this variability is a function of the comparative strengths of the dust and anthropogenic SO2 sources, the transport pathway and in particular the extent to which dust is transported across industrial SO2 sources, and finally, meteorological and chemical processes.

Highlights

During April–May 2006, INTEX-B was focused on the North Pacific with the goal of providing detailed chemical analysis of tropospheric air following a trans-Pacific pathway to the North American continent (e.g. Zhang et al (2008) discuss ozone transport during INTEX-B)
The mobilization and transport of mineral dust from the arid regions of the world is considered of major significance due to the role airborne crustal material plays in the global radiation balance, cloud processes, atmospheric chemistry, oceanic and terrestrial biogeochemical processes, as vectors for microbes, and as a factor influencing local air quality in both “source” and “sink” regions (Prospero et al, 2002)
The mass concentration of coarse particle calcium on 28 April was the second lowest measured during the period, and the increase in coarse particle number concentrations on 28 April is connected to the boundary layer based on the aircraft profiles from that day

Summary

Introduction

During April–May 2006, INTEX-B (the Intercontinental Chemical Transport Experiment) was focused on the North Pacific with the goal of providing detailed chemical analysis of tropospheric air following a trans-Pacific pathway to the North American continent (e.g. Zhang et al (2008) discuss ozone transport during INTEX-B). Zhang et al (2008) discuss ozone transport during INTEX-B) This intensive field campaign, involving ground based, airborne and satellite observations, was prompted by over a decade of observational and modelling studies demonstrating the relatively rapid (especially during springtime) trans-Pacific transport of both crustal material (predominately desert dusts) and anthropogenic pollutants from sources in Eurasia to North America Such pollutants are often mixed into, and interact with, the dust plumes as they pass over urban/industrial sources (LiJones and Prospero, 1998; Heald et al, 2006).

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Conclusion