Characterization of Fine Particulate Matter Emitted from the Resuspension of Road and Pavement Dust in the Metropolitan Area of São Paulo, Brazil

Effects of boundary layer variations on physicochemical characteristics of aerosols in mid-low-altitude regions

Variations in the height of the boundary layer have a critical impact on the vertical transport of near-surface aerosols. Variations can affect the interactions between aerosols and clouds/fog by altering the scattering and absorption of solar radiation, significantly changing radiative forcing, convective precipitation, and regional climate. In this study, we simultaneously monitored air pollution and meteorological factors in a flat urban area (YunTech site, 50 m asl) and its peripheral mountainous region (MeiShan site, 980 m asl), analyzed the characteristics of pollutants under different atmospheric conditions, and explored the differences in the chemical reaction mechanisms of aerosols at various altitudes, aiming to clarify the evolution of the boundary layer in urban and suburban areas and its impact on the transport of pollutants. The results show that even without anthropogenic emissions, urban ground-level pollutants could be transported to peripheral mountainous areas through boundary layer height variations and local circulations, such as mountain-valley breezes. The PM2.5 concentration was higher at the urban site (average 31.14 ± 14.82μgm-3) and could be transported aloft by valley winds, leading to the gradual accumulation of daytime PM2.5 with an afternoon peak at the mountain site. Moreover, the nitrogen oxidation rate (NOR = [NO3-]/[NO3-] + [NO2]) exhibited clear site variations, the mountain site (average 0.41 ± 0.20) was higher than the urban site (average 0.19 ± 0.07), likely due to the atmospheric environment with thick clouds/fog and strong oxidation capacity in the mountain area. Our study has verified that aerosol characteristics, origins, formation pathways and transport mechanisms at the two measurement sites are significantly different under different conditions, which provides a theoretical basis for future air pollution prevention and regional climate research.

A benchmark dataset for binary segmentation and quantification of dust emissions from unsealed roads

The generation of reference data for machine learning models is challenging for dust emissions due to perpetually dynamic environmental conditions. We generated a new vision dataset with the goal of advancing semantic segmentation to identify and quantify vehicle-induced dust clouds from images. We conducted field experiments on 10 unsealed road segments with different types of road surface materials in varying climatic conditions to capture vehicle-induced road dust. A direct single-lens reflex (DSLR) camera was used to capture the dust clouds generated due to a utility vehicle travelling at different speeds. A research-grade dust monitor was used to measure the dust emissions due to traffic. A total of ~210,000 images were photographed and refined to obtain ~7,000 images. These images were manually annotated to generate masks for dust segmentation. The baseline performance of a truncated sample of ~900 images from the dataset is evaluated for U-Net architecture.

Estimation of Pollution Levels and Assessment of Human Health Risks from Potentially Toxic Metals in Road Dust in Mymensingh City of Bangladesh

The assessment of toxic metals pollution in road dust in Mymensingh city, Bangladesh and its impact on the health risk of human exposure to toxic metals, is inadequate. A comprehensive investigation was conducted in different land use areas, i.e., commercial areas (CA), medically facilitated areas (MFA), residential areas (RA), and park areas (PA), to determine levels of Cr (chromium), Mn (manganese), Ni (nickel), Co (cobalt), Cu (copper), Zn (zinc), As (arsenic), Cd (cadmium), and Pb (lead) using inductively coupled plasma mass spectroscopy (ICP-MS). We planned to use different pollution indices, such as the geoaccumulation index (Igeo), contamination factor (CF), degree of contamination (Cdeg), ecological risk (Er), pollution load index (PLI), and enrichment factor (EF), to measure the level of contamination in the road dust of Mymensingh City. The average concentration (mg/kg) ranges of toxic metals in the road dust at different land use areas of Mymensingh City were: Cr (40.8–85.5), Mn (370.7–589.2), Co (6.2–8.7), Ni (22.7–34.2), Cu (29.5–72.2), Zn (236.2–467.1), As (4.9–6.29), Cd (0.32–1.07), and Pb (27.4–81.7), respectively. The CF and PLI results showed that the road dust in these zones was contaminated with toxic metals. The indicator Igeo revealed that CA was found to be ‘moderately to heavily contaminated’ ranked with Zn and Cd. Calculation of EF indicated that Cu, Zn, As, Cd, and Pb were highly enriched, while others were moderately enriched. According to the Cdeg findings, CA, MFA, and RA have very high degrees of contamination (Cdeg ≥ 24), while PA was classified as having a considerable degree of contamination (12 ≤ Cdeg < 24). The Er index showed that only Cd posed a ‘medium potential ecological risk’ to a ‘high ecological potential risk’ in road dust. The most common route of exposure was ingestion. The study indicated that the hazard quotient (HQ) and hazard index (HI) in CA, MFA, RA, and PA were less than one for children and adults, which were at a noncarcinogenic risk. The only exception was for children exposed to manganese (HI > 1) in all land use areas. In the research area, no significant carcinogenic health risk was observed for Cr, Ni, As, Cd, and Pb.

Chemical characterization of PM2.5 from region highly impacted by hailstorms in South America

The chemical composition of particulate material plays an important role in the atmosphere, providing cloud and ice nuclei for storm development. This study aims to evaluate and infer the sources of ions, metals, and metalloids in the fine atmospheric particulate matter (PM_2.5) from triple border Paraná, Santa Catarina (Brazil), and northeastern Argentina, which is among those with the highest hail incidence in the world. Among the ions, the concentrations presented the following sequence in decreasing order: [Formula: see text]> K⁺> [Formula: see text]> [Formula: see text]> Ca²⁺> Cl^-> Na⁺> Mg²⁺. Regarding the metals and metalloid concentrations, the order was of S > Si > Al > Fe > P > Ti, Cr, Cu, and Zn > Br > Mn, and Ni. The main sources, supported by positive matrix factorization results, are soil and agricultural activities, as well as vehicular emissions due to the agricultural machinery and the displacement of residents. Besides, the influence of aerosols from biomass burning and industrial activities was observed, possibly come from long-distance transport. The composition of PM_2.5 presents one or more elements considered present ice nuclei (IN) activity, such as Al, Mn, Cu, Co, Ni, and V (in form of oxides), corroborating with other studies, also, with high hail incidence. However, further studies are needed to verify the role of aerosol characteristics in the formation of IN and, consequently, hail.

Spatial Distribution and Chemical Composition of Road Dust in Two High-Altitude Latin American Cities

Road dust (RD) resuspension is one of the main sources of particulate matter in cities with adverse impacts on air quality, health, and climate. Studies on the variability of the deposited PM10 fraction of RD (RD10) have been limited in Latin America, whereby our understanding of the central factors that control this pollutant remains incomplete. In this study, forty-one RD10 samples were collected in two Andean cities (Bogotá and Manizales) and analyzed for ions, minerals, and trace elements. RD10 levels varied between 1.8–45.7 mg/m2, with an average of 11.8 mg/m2, in Bogotá and between 0.8–26.7 mg/m2, with an average of 5.7 mg/m2, in Manizales. Minerals were the most abundant species in both cities, with a fraction significantly larger in Manizales (38%) than Bogotá (9%). The difference could be explained mainly by the complex topography and the composition of soil derived from volcanic ash in Manizales. The volcanic activity was also associated with SO4−2 and Cl−. Enrichment factors and principal component analysis were conducted to explore potential factors associated to sources of RD10. Elements such as Cu, Pb, Cr, Ni, V, Sb, and Mo were mainly associated with exhaust and non-exhaust traffic emissions.

Edible weeds: Are urban environments fit for foraging?

Foraging wild-growing edible plants (WEPs) is a re-emerging practice with increasing popularity worldwide, including in urban areas. However, in cities, this practice raises questions about the safety of foraging these plants for human consumption, due to the potential exposure of plants to higher levels of pollutants. In this study, the concentration of 12 elements (Al, V, Cr, Mn, Co, Ni, Zn, As, Rb, Cd, Ba and Pb) in three different WEPs (Amaranthus spp., Plantago tomentosa and Taraxacum officinale) were determined according to different traffic categories in the municipality of São Paulo. Additionally, plants were sampled within the inner areas of three municipal parks in the same study region. Different gradients of elemental concentrations were obtained according to the traffic categories. Freeways presented higher concentrations of several elements than local roads or parks. For the WEPs collected along freeways and some plants along arterial roads, the concentrations of Pb exceeded safety levels for human consumption. Our data suggest that foraging in large urban centres should be performed preferentially in low-traffic areas.

Evaluating Atmospheric Pollutants from Urban Buses under Real-World Conditions: Implications of the Main Public Transport Mode in São Paulo, Brazil

The broad expanse of the urban metropolitan area of São Paulo (MASP) has made buses, the predominant public transport mode for commuters in the city. In 2016, the bus fleet in the MASP reached 56,354 buses and it was responsible for more than 12 million daily trips. Here, we evaluate for the first time, the emission profile of gaseous and particulate pollutants from buses running on 7% biodiesel + 93% petroleum diesel and their spatial distribution in the MASP. This novel study, based on four bus terminal experiments, provides an extensive analysis of atmospheric pollutants of interest to public health and climate changes, such as CO2, CO, NOx, VOCs, PM10, PM2.5 and their constituents (black carbon (BC) and elements). Our results suggest that the renovation of the bus fleet from Euro II to Euro V and the incorporation of electric buses had a noticeable impact (by a factor of up to three) on the CO2 emissions and caused a decrease in NO emissions, by a factor of four to five. In addition, a comparison with previous Brazilian studies, shows that the newer bus fleet in the MASP emits fewer particles. Emissions from the public transport sector have implications for public health and air quality, not only by introducing reactive pollutants into the atmosphere but also by exposing the commuters to harmful concentrations. Our findings make a relevant contribution to the understanding of emissions from diesel-powered buses and about the impact of these new vehicular technologies on the air quality in the MASP.

WRF-SMOKE-CMAQ modeling system for air quality evaluation in São Paulo megacity with a 2008 experimental campaign data

Atmospheric pollutants are strongly affected by transport processes and chemical transformations that alter their composition and the level of contamination in a region. In the last decade, several studies have employed numerical modeling to analyze atmospheric pollutants. The objective of this study is to evaluate the performance of the WRF-SMOKE-CMAQ modeling system to represent meteorological and air quality conditions over São Paulo, Brazil, where vehicular emissions are the primary contributors to air pollution. Meteorological fields were modeled using the Weather Research and Forecasting model (WRF), for a 12-day period during the winter of 2008 (Aug. 10th-Aug. 22nd), using three nested domains with 27-km, 9-km, and 3-km grid resolutions, which covered the most polluted cities in São Paulo state. The 3-km domain was aligned with the Sparse Matrix Operator Kernel Emissions (SMOKE), which processes the emission inventory for the Models-3 Community Multiscale Air Quality Modeling System (CMAQ). Data from an aerosol sampling campaign was used to evaluate the modeling. The PM₁₀ and ozone average concentration of the entire period was well represented, with correlation coefficients for PM₁₀, varying from 0.09 in Pinheiros to 0.69 in ICB/USP, while for ozone, the correlation coefficients varied from 0.56 in Pinheiros to 0.67 in IPEN. However, the model underestimated the concentrations of PM_2.5 during the experiment, but with ammonium showing small differences between predicted and observed concentrations. As the meteorological model WRF underestimated the rainfall and overestimated the wind speed, the accuracy of the air quality model was expected to be below the desired value. However, in general, the CMAQ model reproduced the behavior of atmospheric aerosol and ozone in the urban area of São Paulo.

Reduced ultrafine particle levels in São Paulo's atmosphere during shifts from gasoline to ethanol use

Despite ethanol’s penetration into urban transportation, observational evidence quantifying the consequence for the atmospheric particulate burden during actual, not hypothetical, fuel-fleet shifts, has been lacking. Here we analyze aerosol, meteorological, traffic, and consumer behavior data and find, empirically, that ambient number concentrations of 7–100-nm diameter particles rise by one-third during the morning commute when higher ethanol prices induce 2 million drivers in the real-world megacity of São Paulo to substitute to gasoline use (95% confidence intervals: +4,154 to +13,272 cm⁻³). Similarly, concentrations fall when consumers return to ethanol. Changes in larger particle concentrations, including US-regulated PM2.5, are statistically indistinguishable from zero. The prospect of increased biofuel use and mounting evidence on ultrafines’ health effects make our result acutely policy relevant, to be weighed against possible ozone increases. The finding motivates further studies in real-world environments. We innovate in using econometrics to quantify a key source of urban ultrafine particles.

The biofuel ethanol has been introduced into urban transportation in many countries. Here, by measuring aerosols in São Paulo, the authors find that high ethanol prices coincided with an increase in harmful nanoparticles by a third, as drivers switched from ethanol to cheaper gasoline, showing a benefit of ethanol.