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 (Canadian Operational Research Aerosol Lidar Network) lidars in Vancouver, BC, and Egbert, ON, with AERONET (AErosol RObotic NETwork) sunphotometer retrievals and model results from HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) and NAAPS (Navy Aerosol Analysis and Prediction System) 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 volume 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 layers of dust were transported across North America the rates of change in their 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

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Abstract. Forest fires in Northern California and Oregon were responsible for two significant regional scale aerosol transport events observed in southern British Columbia during summer 2008. A combination of ground based (CORALNet) and satellite (CALIPSO) lidar, sunphotometry and high altitude chemistry observations permitted unprecedented characterization of forest fire plume height and mixing as well as description of optical properties and physicochemistry of the aerosol. In southwestern BC, lidar observations show the smoke to be mixed through a layer extending to 5-6 km a.g.l. where the aerosol was confined by an elevated inversion in both cases. Depolarization ratios for a trans-Pacific dust event (providing a basis for comparison) and the two smoke events were consistent with observations of dust and smoke events elsewhere and permit discrimination of aerosol events in the region. Based on sunphotometry, the Aerosol Optical Thicknesses (AOT) reached maxima of ∼0.7 and ∼0.4 for the two events respectively. Dubovikretrieval values of r eff,f during both the June/July and August events varied between about 0.13 and 0.15 µm and confirm the dominance of accumulation mode size particles in the forest fire plumes. Both Whistler Peak and Mount Bachelor Observatory data show that smoke events are accompanied by elevated CO and O 3 concentrations as well as elevated K + /SO 4 ratios. In addition to documenting the meteorology and physic-chemical characteristics of two regional scaleCorrespondence to: I. McKendry (ian@geog.ubc.ca) biomass burning plumes, this study demonstrates the positive analytical synergies arising from the suite of measurements now in place in the Pacific Northwest, and complemented by satellite borne instruments.

A ground-based lidar system that has been deployed in Whistler, British Columbia, Canada, since the spring of 2010 provides a means of evaluating vertical aerosol structure in a mountainous environment. This information is used to help to determine when an air chemistry observatory atop Whistler Mountain (2182 m MSL) is within the free troposphere or is influenced by the valley-based planetary boundary layer (PBL). Three case studies are presented in which 1-day time series images of backscatter data from the lidar are analyzed along with concurrent meteorological and air-chemistry datasets from the mountaintop site. The cases were selected to illustrate different scenarios of diurnal PBL evolution that are expected to be common during their respective seasons. The lidar images corroborate assumptions about PBL influence as derived from analysis of diurnal trends in water vapor, condensation nuclei, and ozone. Use of all of these datasets together bolsters efforts to determine which atmospheric layer the site best represents, which is important when evaluating the provenance of air samples.

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