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

Patricia Krecl,Admir Cre´So Targino

doi:10.4209/aaqr.2015.06.0388

Patricia Krecl, Admir Cre´So Targino

Open Access

https://doi.org/10.4209/aaqr.2015.06.0388

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Abstract

ABSTRACTBlack 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 95th 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 (Tair) 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 Tair 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.

Highlights

IntroductionAir pollution concerns affect large cities and mega-metropolises (populations exceeding 10 million) and mid-sized cities, as urban populations within this category have increased considerably over recent years
Today, air pollution concerns affect large cities and mega-metropolises and mid-sized cities, as urban populations within this category have increased considerably over recent years
We investigated the Black carbon (BC) concentrations at three sites of a mid-sized city in southern Brazil and observed a large spatiotemporal variability in the dataset

Summary

Introduction

Air pollution concerns affect large cities and mega-metropolises (populations exceeding 10 million) and mid-sized cities, as urban populations within this category have increased considerably over recent years. Brazilian mid-sized cities –with populations ranging from 100 to 600 thousand– grew between 2000 and 2007, while small and large cities showed a decline in population (IPEA, 2008). The consequences of air quality deterioration for the urban population is more acute in developing countries with a tendency of operating old and badly-maintained. A complicating factor in accurately assessing the concentration of urban air pollutants is that traffic is concentrated in the city’s inner core, which can comprise a complex configuration of canyons, avenues and parks. The combination of designs, materials and geographical attributes impact the air flow within the urban canopy, affecting the concentration of pollutants in this layer.

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