Abstract
The study focuses on the transport of aerosol particles resulting from biomass burning in central South America towards the megacity of Buenos Aires by the South American Low-Level Jet. In particular, the cases are studied in which the exit area of the Jet reaches the La Plata Basin with no precipitation associated, herein called Chaco Jet 1 (CJ1), which could remove aerosols from the atmosphere on their way towards the city. CJ1 events registered within the five-year period of 2001–2005 are examined along with changes in the optical properties of aerosols over the city from measurements from the Aerosol Robotic Network (AERONET) site. Three-dimensional backward trajectories of CJ1 were obtained to verify the connection between the receptor site and the biomass-burning source region. A cluster analysis of the trajectories allows further characterizing the features and impacts of regionally transported aerosols. A subsample of days on which impacts of the contribution of biomass burning could have occurred, showed a statistically significant increase in aerosol optical depth and Ångström exponent, reflected by an increase in the peak of the derived volume size distribution in the fine fraction size range, which also shifts slightly towards bigger radii. The days with AOD greater than 0.15 show overall behaviour like other urban sites with pollution of different origins. The evaluation of the selected data reveals that higher values of AOD and changes in the Ångström exponent are linked to the dispersion of biomass-burning aerosols. Air mass trajectories coinciding with the CJ1 core present the strongest impact on aerosol characteristics, which can be seen in spectral measurements.
Highlights
Introduction e city of Buenos Aires is located on the southern shore of the Rıo de la Plata river. e city together with the 24 counties of the Greater Buenos Aires (GBA) is the third largest metropolitan area in South America with a population of nearly 13 million inhabitants [1]
Mean Aerosol optical depth (AOD) and its standard deviation are greater during the biomassburning season, which extends from August to October, with slightly higher values in August
E selection of events meeting the set of criteria, i.e., with possible regional transport of biomass-burning products towards Buenos Aires, made it possible to identify a total of 68 days within the five-year period under analysis
Summary
Received 25 January 2019; Revised 23 June 2019; Accepted 22 November 2019; Published 29 December 2019. A preliminary study reported noticeable increases in mean AOD and Angstrom exponent during CJ1 events during the biomass-burning season using AERONET V2.0 data [14]. Studies of the role of the SALLJ in the regional transport of biomass-burning products in 2002 using observational data and modelling tools provided a detailed three-dimensional structure and evolution of the meteorological and aerosol fields [10, 15]. Eck et al [21] showed that biomass burning and urban aerosols exhibit large spectral variations of the Angstrom exponent at moderate to large optical depths due to the dominance of fine mode sized particles. E results reported in the present paper are intended to contribute to the understanding of aerosol optical properties in the atmosphere of Buenos Aires and to document the impact on those properties of regional flow during aerosol transport from remote sources. Gobbi et al [24] assume a bimodal aerosol size distribution, and their analysis of the sensitivity to the refractive index
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