Smoke plume optical properties and transport observed by a multi-wavelength lidar, sunphotometer and satellite Yonghua Wu * , Lina Cordero, Barry Gross, Fred Moshary, Sam Ahmed Optical Remote Sensing Lab, City College of New York, New York, NY 10031, USA highlights < Smoke plumes optical properties and temporal-spatial distributions are presented. < Intra-continental transport and origins of smoke plumes are investigated. < Influences on the PBL and surface PM2.5 by smoke-plumes are illustrated. article info Article history: Received 18 July 2012 Received in revised form 8 September 2012 Accepted 10 September 2012 Keywords: Smoke Transport Optical properties Lidar Satellite abstract Optical characteristics and long-distance transport of smoke plumes are studied using satellite obser- vations and ground-based remote sensing in New York City. Vertical distribution and column optical properties of aerosol plume are derived from a combination of multi-wavelength lidar and sunpho- tometer measurement. Aloft smoke plumes from two cases are investigated in this paper from U.S. western and south-western forest fires. The smoke source and transport pathway to the U.S. east coast are analyzed by MODIS and CALIOP imageries as well as HYSPLIT backward trajectory analysis. In both cases, the plumes have relatively high optical depth (as much as 1.2 at 500-nm) and Angstrom exponent of up to 1.8, but show different intrusion heights, source regions and transport process. Lidar profiling observations indicate these smoke plumes mixing downward into the planetary-boundary-layer which are coincident with increasing trends of surface PM 2.5 (particulate matter, diameter < 2.5 mm) concentrations. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Forest-fire and biomass burning often inject large amounts of smoke aerosols into the atmosphere, which are elevated to the free troposphere and transported over long distances (Forster et al., 2001; Hoff et al., 2005). Smoke plumes can also subside into the planetary-boundary-layer (PBL) during the transport (Colarco et al., 2004; Colette et al., 2008; Duck et al., 2007). Observations indicate that aerosol plumes potentially modify cloud physical, chemical and optical properties (Kaufman et al., 2005). As such, smoke plumes affect the climate, air quality and visibility in the regional and continental scale. The occurrence, transport and column optical properties of smoke plumes have been extensively investigated by satellite-borne radi- ometers (Kaufman et al., 2003; Kahn et al., 2007). Vertical structure and optical characteristic of aerosol plumes have also been observed by lidar (Müller et al., 2005; Duck et al., 2007). For example, the transport of plumes from California forest fires to the northeastern U.S. was captured by the Geoscience Laser Altimeter System on ICESat (Hoff et al., 2005). In particular, with dual-wavelength Raman lidar measurements, smoke particle size and a high wavelength depen- dence of lidar-ratio (extinction-to-backscatter ratio) were found to be strongly associated with the fire type, strength and transport process (Müller et al., 2005). However, in the daytime, the capability of a Raman lidar in measuring aerosol is largely limited in the lower troposphere because of its inherent weak signal-to-noise ratio (SNR) caused by strong daylight noise (Ferrare et al., 2006). Under this situation, a combination of elastic lidar and sunphotometer measurements can provide the constraint of aerosol extinction and backscatter profile (Pelon et al., 2002) and thereby facilitate the aloft smoke plume retrievals in the daytime measurement. In this study, the combined observations of smoke plumes from a ground-based multi-wavelength lidar, sun/sky radiometer and satellite sensors MODIS (Moderate Resolution Imaging Spectror- adiometer) and CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) on CALIPSO are presented. We focus on two events to retrieve aerosol plumes optical characteristics and track their * Corresponding author. E-mail address: yhwu@ccny.cuny.edu (Y. Wu). Contents lists available at SciVerse ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.atmosenv.2012.09.016 Atmospheric Environment 63 (2012) 32e42