Richard A. VanCuren

Asian aerosols in North America: Frequency and concentration of fine dust

average) are between 0.2 and 1 mg/m 3 and only very rarely exceed 5 mg/m 3 . Our data also indicate that Asian dust is concentrated in an altitude zone ranging from about 500 to 3000 m MSL, consistent with isentropic transport processes previously observed in the western Pacific. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; KEYWORDS: dust, Asia, North America, aerosol, troposphere

Pb Isotopes as an Indicator of the Asian Contribution to Particulate Air Pollution in Urban California

During the last two decades, expanding industrial activity in east Asia has led to increased production of airborne pollutants that can be transported to North America. Previous efforts to detect this trans-Pacific pollution have relied upon remote sensing and remote sample locations. We tested whether Pb isotope ratios in airborne particles can be used to directly evaluate the Asian contribution to airborne particles of anthropogenic origin in western North America, using a time series of samples from a pair of sites upwind and downwind of the San Francisco Bay Area. Our results for airborne Pb at these sites indicate a median value of 29% Asian origin, based on mixing relations between distinct regional sample groups. This trans-Pacific Pb is present in small quantities but serves as a tracer for airborne particles within the growing Asian industrial plume. We then applied this analysis to archived samples from urban sites in central California. Taken together, our results suggest that the analysis of Pb isotopes can reveal the distribution of airborne particles affected by Asian industrial pollution at urban sites in northern California. Under suitable circumstances, this analysis can improve understanding of the global transport of pollution, independent of transport models.

Correction to “Asian aerosols in North America: Frequency and concentration of fine dust”

[1] Using an elemental signature for Asian dust derived from events in April 1998, we probed a long-term set of routine aerosol samples to develop the first empirical assessment of the frequency and intensity of dust transport from Asia to midlatitude North America. Our data reveal a pattern of consistent, frequent transport that contradicts the episodic characterization derived from short-term studies and anecdotal reports. We find that fine (<2.5 mm) Asian dust is a regular component of the troposphere over the eastern Pacific and western North America and is common, at least in spring, across North America. Typical Asian fine dust concentrations (24-hour average) are between 0.2 and 1 mg/m and only very rarely exceed 5 mg/m. Our data also indicate that Asian dust is concentrated in an altitude zone ranging from about 500 to 3000 m MSL, consistent with isentropic transport processes previously observed in the western Pacific.