A pervasive and persistent Asian dust event over North America during spring 2010: lidar and sunphotometer observations

Abstract

Among the many well-documented cases of springtime trans-Pacific transport of crustal dust from Asia to North America (significant events include those of 1998, 2001, and 2005), the events of March and April 2010 were extraordinary both in the extent of the dust distribution and in the unique meteorological conditions that caused the dust layers in the free troposphere to linger and be detectable across Canada and the Northern United States for over a month. This study focuses on extending previous research by combining data from CORALNet lidars in Vancouver, BC and Egbert, ON with AERONET sunphotometer retrievals and model results from HYSPLIT and NAAPS to monitor the arrival and distribution of dust layers across North America. This is the first documented instance of lidar detection of Asian dust from the Egbert CORALNet installation, where layers identified as dust using depolarization ratios corresponded with retrievals of coarse mode optical depth at the co-located AEROCAN/AERONET site. In Vancouver dust layer depolarization ratios varied from 0.27 for dust above 6 km to less than 0.10 for the first 1.5–2 km above the surface. Similar layers of elevated dust exhibited much lower bulk depolarization ratios for all altitudes in Egbert, ON where maximum depolarization ratios stayed below 0.15 for all layers from 2–8 km with no clear variation with altitude, or over time. The relative lack of variation is an indication that as the dust particles aged the rate of change in chemical composition and optical properties slowed. HYSPLIT back trajectories performed throughout the free troposphere above these sites showed a majority of air parcels originating from Central Asia on the days in question. Using these techniques, it was shown that elevated layers of aerosol reaching the west coast of North America as early as 17 March also included dust from the same Central Asian sources, extending the known duration of the 2010 event by almost a full month

Spatial and seasonal variability in fine mineral dust and coarse aerosol mass at remote sites across the United States

“…Interestingly, the spring Asian FD influence may have extended as far east as the Boundary Waters and Northeast regions, where a spring decoupling in FD and CM was also observed (Figure ). Asian dust impacts in the northeast previously have been observed [ Debell et al ., ; Cottle et al ., ], as well as dust transport from the Southwest [ Park et al ., ]. All regions in the East experienced a seasonal decoupling of FD and CM, with the mid‐South, Southeast, Appalachia, and Ohio River Valley regions having strong FD maxima in summer, likely associated with North African dust transport.…”

Frequency and Character of Extreme Aerosol Events in the Southwestern United States: A Case Study Analysis in Arizona

“…A suite of previous studies discussing source attribution of aerosol to long-range transport from Asia to North America have relied on NAAPS. For example, Cottle et al [ 31 ] used NAAPS with HYSPLIT back-trajectories, and sunphotometer and lidar data to show that springtime dust plumes from Asia reached North America. Wu et al [ 32 ], more recently, used NAAPS and remotely-sensed data from CALIPSO to study a trans-Pacific Asian dust event and its impact on the east coast of the United States.…”

Dust Aerosols Detected Using a Ground-Based Polarization Lidar and CALIPSO over Wuhan (30.5°N, 114.4°E), China

“…Enough time is provided for the dust particles to externally and internally mix with other urban aerosols. Cottle et al [57] observed the maximum volume depolarization ratio within the dust layers reduced substantially from 0.27 over Vancouver to 0.15 over Egbert by the time the dust layers travelled across North America during April 2010. They explained this finding that was the result of continued loss of dust, external mixing with the background aerosol layer or more likely a combination of both.…”