Local and Regional Contributions to Black Carbon Aerosols in a Mid-Sized City in Southern Brazil

ABSTRACT

Black carbon (BC) concentrations were monitored at three sites (suburban, street canyon and urban rooftop) in a mid-sized Brazilian city, from August 2014 to January 2015. The suburban site presented weak diurnal cycles, suggesting little influence of motorized traffic, but distinctively large 95^th percentile concentrations, reaching values as large as 11.04 and 3.34 µg m^–3 in the evenings of the dry and wet season (respectively), likely attributable to local waste burning. Moreover, higher BC concentrations at the suburban site were observed throughout the dry period, primarily caused by long-range transport (LRT) of smoke from the central part of Brazil and neighboring countries, carried by WNW, SSW and NNE winds. Local traffic was by far the most important source of BC in  street canyon, with mean hourly peaks of 5.8 µg m^–3 (at 7:00) and 4.6 µg m^–3 (18:00), coinciding with rush hour periods. The rooftop data showed a mean peak of 1.4 µg m^–3 at 7:00, reflective of traffic on a busy avenue adjacent to the site. Meteorological data clustered into groups of similar air temperature (T_air) and relative humidity (RH) showed that BC concentrations were highest (18.3 µg m^–3) at the suburban site during the evenings of dry (RH ca. 20%) and hot days (maximum T_air ca. 30°C). Diurnal concentrations in the canyon and rooftop were linked to traffic patterns and showed no clear linkage to meteorological conditions.    This study shows that the BC concentrations in the city are highly variable and that air quality diminishes considerably due to sporadic waste burning and LRT of biomass smoke, even in neighborhoods with little motor traffic. While air pollution due to transboundary smoke is more difficult to abate, these results suggest that targeting local backyard burning and traffic volume would lead to a depletion of BC concentrations in the city.