Observations of particulate matter, NO2, SO2, O3, H2S and selected VOCs at a semi-urban environment in the Amazon region

Weather impact on ambient air pollution and its association with land use types/activities over 5,572 municipalities in Brazil

Quantify the impact of meteorological changes on air pollution levels is the aim of numerous recent studies. However, there is still a lack of investigations assessing the influence of land use/activities on the relationship between climate and air quality. In this study, we used a two-stage design to estimate the influence of land use types and activities on the association between weather changes and air pollution (PM2.5, NO2, SO2, O3) over 5572 municipalities in Brazil. To calculate the influence of recent weather change on air pollution concentration for each municipality, we used the "weather penalty" concept. This approach considers differences in linear trend coefficients between two generalized additive models. Then, using quantile regression, we estimated the effect of land use types and activities (8 variables related to transportation, energy generation, and land use) on weather-related increases in ambient air pollution. We found that an increase in PM2.5 was associated to recent weather changes in most municipalities (average increase of 0.07μg/m3per year) and a decrease in NO2 in most municipalities (average decrease of 0.0003 ppb per year). O3 and SO2 had more intense increases associated with weather changes in the North region. Our findings suggest the most robust positive associations between weather penalties on PM2.5 and areas with non-clean energy and oil refineries (average increase of 0.006μg/m3per year and 0.04μg/m3per year, respectively). We also found positive associations between Pasture areas, urban areas, and transportation and the weather penalties of this pollutant. In contrast, forest areas were negatively associated with PM2.5 penalties. We also found that oil refineries, urban areas, and transportation significantly positively influenced weather penalties for SO2 and O3. Overall, the study highlights the importance of considering the influence of land use types and activities on weather-related changes in ambient air pollution.

Ecotoxicological assessments of atmospheric biomonitors exposed to urban pollution in a Brazilian metropolis

Subcellular metal distribution assessments are the most adequate biomonitoring approach to evaluate metal toxicity, instead of total metal assessments This study aimed to assess subcellular metal distributions and associations to the main metal exposure biomarker, metallothionein (MT), in two bromeliad species (Tillandsia usneoides and Tillandsia stricta) exposed established in industrial, urban, and port areas in the metropolitan region of Rio de Janeiro, southeastern Brazil, through an active biomonitoring approach conducted one year. Metals and metalloids in three subcellular fractions (insoluble, thermolabile and thermostable) obtained from the MT purification process were determined by inductively coupled plasma mass spectrometry (ICP-MS). Lower MT concentrations were observed both during the dry sampling periods, associated to the crassulacean acid metabolism (CAM) and during the COVID-19 pandemic, due to reduced urban mobility, decreasing pollutant emissions. The percentage of non-bioavailable metals detected in the insoluble fraction increased throughout the sampling period for both species. Several metals (Cr, Co, Cu, Cd, Mn, Ni, Se, and Zn), most associated with vehicle emissions, the main pollutant source in urban centers, were detected in the thermostable fraction and are, thus, associated with MT through the MT-metal detoxification route. Insoluble metal concentrations were higher in T. stricta, indicating that this species seems less susceptible to cellular metal exposure damage. A potential protective effect of Se and Fe was detected against Pb, suggested by a strong negative correlation, which may be attributed to antioxidant roles and similar uptake routes, respectively.

A novel low sampling rate and cost-efficient active sampler for medium/long-term monitoring of gaseous pollutants

Active sampling is a dependable approach for gaseous pollutants monitoring, offering high accuracy and precision that is unaffected by environmental factors such as wind and temperature in comparison to passive sampling. To measure long-term average concentrations while minimizing the use of materials, a reduced sampling rate is necessary. Thus, this study aims to develop a novel low sampling rate (down to 1 mL/min) and cost-efficient active sampler (LASP) for medium/long-term monitoring of gaseous pollutants. The LASP mainly consisted of a syringe pump, a Y-shaped fitting with two one-way valves, and a control unit for intermittent operation. Results showed that LASP can obtain a sampling rate of less than 1 mL/min and sampling rate exhibited a high level of stability. Daily average concentrations measurements for nitrogen dioxide and formaldehyde by LASP had normalized mean biases of 2.8% and 5.2%, respectively. These numbers were - 5.8% and 6.1% for weekly-average samplings. This study demonstrated applications of LASP in real outdoor (daily-average) and indoor (weekly-average) air quality measurements. It worked well with low noise levels, and without interfering with occupants' daily activities. LASP can assist in improving our ability to monitor air quality and pollutants emissions, thereby supporting health research and policy development. ENVIRONMENTAL IMPLICATION: Gaseous air pollution is an important hazardous factor threatening human health. Medium/long-term air quality monitoring is essential for outdoor and indoor air quality assessment and control. However, air sampler for medium/long-term sampling is lacking. This study developed a novel low sampling rate and cost-efficient active sampler and applied it to medium/long-term air sampling. The sampler can work at a sampling rate of less than 1 mL/min. This technology provides a feasible strategy for medium/long-term monitoring of gaseous air pollutants in both environments and emission hotspots.

Metal Oxide Semiconductor Nanostructure Gas Sensors with Different Morphologies

There is an increasing need for the development of low-cost and highly sensitive gas sensors for environmental, commercial, and industrial applications in various areas, such as hazardous gas monitoring, safety, and emission control in combustion processes. Considering this, resistive-based gas sensors using metal oxide semiconductors (MOSs) have gained special attention owing to their high sensing performance, high stability, and low cost of synthesis and fabrication. The relatively low final costs of these gas sensors allow their commercialization; consequently, they are widely used and available at low prices. This review focuses on the important MOSs with different morphologies, including quantum dots, nanowires, nanofibers, nanotubes, hierarchical nanostructures, and other structures for the fabrication of resistive gas sensors.

Fluxes of H2S and SO2 above a subtropical forest under natural and disturbed conditions induced by temporal land-use change

Hydrogen sulfide (H₂S) is one of predominant biogenic sulfur gases, influencing aerosol formation and climate change. There is considerable uncertainty of the global budget of H₂S due to limited field data, especially in subtropical forests. In addition, an interaction between soil-emitted H₂S and ambient sulfur dioxide (SO₂) might exist within forest ecosystems. In this study, the aerodynamic gradient method was applied to consecutively measure H₂S and SO₂ fluxes above a subtropical forest canopy in Southwest China under natural and disturbed conditions induced by temporal land-use changes. The average H₂S concentration and flux under natural conditions were 0.79 ± 0.07 ppbv and 0.04 ± 0.01 g S m^-2 yr^-1, respectively. The emission was larger than that in most croplands and freshwater wetlands. Vegetation emissions might account for about 26% of the total forest H₂S emissions at this site. The deposition of SO₂ was likely balanced by H₂S oxidization under the forest canopy, with the mean concentration and net flux as 1.23 ± 0.11 ppbv and -0.03 ± 0.10 g S m^-2 yr^-1, respectively. Under disturbed conditions with soils excavation and scattering on the forest floor, simultaneously high emissions of H₂S and SO₂ were observed above the canopy, reaching 5.78 ± 0.16 and 1.60 ± 0.87 g S m^-2 yr^-1, respectively. This suggested that land-use change in subtropical forests might lead to release of legacy S in subsoils to the atmosphere in the form of H₂S and SO₂. Regarding the widely documented large S accumulation and expanding deforestation across subtropical forests, potentially high emissions of H₂S and SO₂ from subtropical forests should be carefully considered in regional air quality control and forest management.

Accelerated toluene degradation over forests around megacities in southern China

Toluene is a typical anthropogenic pollutant that has profound impacts on air quality, climate change, and human health, but its sources and sinks over forests surrounding megacities remain unclear. The Nanling Mountains (NM) is a large subtropical forest and is adjacent to the Pearl River Delta (PRD) region, a well-known hotspot for toluene emissions in southern China. However, unexpectedly low toluene concentrations (0.16 ± 0.20 ppbv) were observed at a mountaintop site in NM during a typical photochemical period. A backward trajectory analysis categorized air masses received at the site into three groups, namely, air masses from the PRD, those from central China, and from clean areas. The results revealed more abundant toluene and its key oxidation products, for example, benzaldehyde in air masses mixed with urban plumes from the PRD. Furthermore, a more than three times faster degradation rate of toluene was found in this category of air masses, indicating more photochemical consumption in NM under PRD outflow disturbance. Compared to the categorized clean and central China plumes, the simulated OH peak level in the PRD plumes (15.8 ± 2.2 × 106 molecule cm-3) increased by approximately 30% and 55%, respectively, and was significantly higher than the reported values at other background sites worldwide. The degradation of toluene in the PRD plumes was most likely accelerated by increased atmospheric oxidative capacity, which was supported by isoprene ozonolysis reactions. Our results indicate that receptor forests around megacities are not only highly polluted by urban plumes, but also play key roles in environmental safety by accelerating the degradation rate of anthropogenic pollutants.

Spatiotemporal characteristics of NO2, PM2.5 and O3 in a coastal region of southeastern China and their removal by green spaces

Understanding the spatio-temporal characteristics of air pollutants is essential to improving air quality. One aspect is the question of whether green spaces can reduce air pollutant concentrations. However, previous studies on this issue have reported mixed results. This study analyzed the spatio-temporal characteristics of NO₂, PM_2.5 and O₃ in Fujian Province, Southeast China in 2015. In order to reduce uncertainties in the conclusions drawn, the effects landscape metrics describing green spaces have on air pollutants have been analyzed using Pearson correlation analysis at six different spatial scales for the four seasons, considering the influence of meteorological conditions. The results show that PM_2.5 and O₃ are major pollutants whose relative importance varies with the seasons. Significant differences in pollutant concentrations were observed in suburban and urban areas, highlighting the importance of ensuring a reasonable spatial distribution of monitoring stations. Moreover, significant correlations between air pollutants and green space landscape patterns during the four seasons were found, revealing increased air pollutant concentrations with increasing landscape fragmentation and reduced connectivity and aggregation. This probably indicates that interconnected green spaces have the potential to improve air quality. Utilizing green space function regulations can alleviate NO₂ and PM_2.5 pollution effectively, but it is still difficult to reduce O₃ concentrations because green spaces are likely to not only serve as sinks for O_3, but can also promote O₃ formation.

Metabolic and physiological alterations indicate that the tropical broadleaf tree Eugenia uniflora L. is sensitive to ozone

Eugenia uniflora L. is an important fruit tree native to tropical South America that adapts to different habitats, thanks to its metabolic diversity and ability to adjust the leaf antioxidant metabolism. We hypothesized that this metabolic diversity would also enable E. uniflora to avoid oxidative damage and tolerate the enhanced ozone (O3) concentrations that have been registered in the (sub)tropics. We investigated whether carbohydrates, polyphenols and antioxidants are altered and markers of oxidative damage (ROS accumulation, alterations in leaf gas exchange, growth and biomass production) are detected in plants exposed to two levels of O₃ (ambient air and twice elevated ozone level in a O₃-FACE system for 75 days). Phytotoxic O₃ dose above a threshold of 0 nmol m^-2 s^-1 (POD0) and accumulated exposure above 40 ppb (AOT40) were 3.6 mmol m^-2 and 14.898 ppb h at ambient, and 4.7 mmol m^-2 and 43.881 ppb h at elevated O₃. Twenty-seven primary metabolites and 16 phenolic compounds were detected in the leaves. Contrary to the proposed hypothesis that tropical broadleaf trees are relatively O₃ tolerant, we concluded that E. uniflora plants are sensitive to elevated O₃ concentrations. Experimental POD0 values were lower than the critical levels for visible foliar O₃, because of low stomatal conductance. In spite of this low stomatal O₃ uptake, we found classic O₃ injury, e.g. reduction in carbohydrates and fatty acids concentrations; non-significant changes in the polyphenol profile; inefficient antioxidant responses; increased contents of ROS and indicators of lipid peroxidation; reductions in stomatal conductance, net photosynthesis, root/shoot ratio and height growth. However, we also found some compensation mechanisms, e.g. increased leaf concentration of polyols for protecting the membranes, and increased leaf number for compensating the decline of photosynthetic rate. These results help filling the knowledge gap about tropical tree responses to O₃.

Avoidable mortality by implementing more restrictive fine particles standards in Brazil: An estimation using satellite surface data

A growing number of epidemiological studies have been affirming the linking between fine particles (PM_2.5) and deaths due to diverse causes as a result of long-term exposure. This work demonstrates the benefits of improving air quality policies by evaluating the impact of PM_2.5 in terms of avoidable mortality due to all causes, cardiopulmonary causes, and lung cancer, between 2014 and 2018, for 5570 Brazilian cities. Satellite annual surface PM_2.5 concentrations were compared with available monitoring measurements and used as the baseline scenario. Each phase of the Brazilian air quality legislation (CONAMA 491/2018) was used as a control scenario. The satellite PM_2.5 annual surface levels were slightly lower than the monitoring concentrations, with an average mean bias of -2.7 μg/m³. No annual mean PM_2.5 concentration above 20 μg/m³ was observed in any city in 2014 and 2018. In 2016, 23% of cities exceeded the annual mean concentration of 10 μg/m³. A weak positive correlation was found between city-level PM_2.5 and population, vehicle fleet, number of fire outbreaks, urban area size, Growth Domestic Product per capita, Human Development Index, and life expectancy. During the five years, a total of 48,700 ± 7570 deaths due to all causes, 24,100 ± 3260 due to cardiopulmonary causes, and 1780 ± 435 due to lung cancer could be avoided if the maximum PM_2.5 annual concentration of 10 μg/m³ was not exceeded. Less restrictive standards lead to much lower avoidable deaths. For example, considering the maximum annual concentration of 20 μg/m³, 1335 ± 175 deaths due to all causes could be avoided between 2015 and 2017. Our results indicate the importance of adopting more restrictive air quality standards in Brazil. If the current levels do not protect life as they should be, an effort regarding control emissions, monitoring, and modeling is essential to construct an effective air quality management for the country, aiming to comprehend the current PM_2.5 concentration and to achieve lower standards.

COVID-19 lockdown induced air pollution reduction over India: A lesson for future air pollution mitigation strategies

Air pollution is one of the biggest problems worldwide and needs to be addressed potentially with the implementation of updated stringent policies and legislative laws. The nationwide lockdown imposed to prevent the COVID-19 outbreak, has given us a unique opportunity to understand the contribution of anthropogenic emissions to the total atmospheric pollutant burden on a global as well as regional scale. Thus, in the present study, we try to investigate the impact of COVID-19 induced lockdown on common ambient air pollutants (i.e., PM_2.5, NO₂, and SO₂) concentration over 22 cities in India using in-situ measurement under a network of Centre Pollution and Control Board (CPCB). A significant reduction in the mean mass concentration of all the studied air pollutants (i.e., PM_2.5, NO₂, and SO₂) (nearly 10–70%) is found during different phases of lockdown which reached within the National Ambient Air Quality Standard (i.e., NAAQS). The reduction in studied air pollutants is more prominent during the first phase of lockdown (mainly NO₂) which could be due to the complete shutdown of industrial activities. The outcome of the present study will be helpful for policymakers to design cost-effective and accurate air pollution mitigation strategies for the development of a sustainable environment. The study also suggests that well-planned short-term and periodical lockdown could be an alternative effective tool of air pollution mitigation.

CO2, CO, hydrocarbon gases and PM2.5 emissions on dry season by deforestation fires in the Brazilian Amazonia

The rate of deforestation in Brazil increased by 29% between 2015 and 2016, resulting in an increase of greenhouse gas emissions (GHG) of 9%. Deforestation fires in the Amazonia are the main source of GHG in Brazil. In this work, amounts of CO₂, CO, main hydrocarbon gases and PM_2.5 emitted during deforestation fires, under real conditions directly in Brazilian Amazonia, were determined. A brief discussion of the relationship between the annual emission of CO₂ equivalent (CO_2,eq) and Paris Agreement was conducted. Experimental fires were carried out in Western Amazonia (Candeias do Jamari, Rio Branco and Cruzeiro do Sul) and results were compared with a previous fire carried out in Eastern Amazonia (Alta Floresta). The average total fresh biomass on the ground before burning and the total biomass consumption were estimated to be 591 ton ha^-1 and 33%, respectively. CO₂, CO, CH₄, and non-methane hydrocarbon (NMHC) average emission factors, for the four sites, were 1568, 140, 8, and 3 g kg^-1 of burned dry biomass, respectively. PM_2.5 showed large variation among the sites (0.9-16 g kg^-1). Emissions per hectare of forest were estimated as 216,696 kg of CO₂, 18,979 kg of CO, 1,058 kg of CH₄, and 496 kg of NMHC. The average annual emission of equivalent CO₂ was estimated as 301 ± 53 Mt year^-1 for the Brazilian Amazonia forest. From 2013, the estimated CO_2,eq showed a trend to increase in Amazon region. The present study is an alert and provides important information that can be used in the development of the public policies to control emissions and deforestation in the Brazilian Amazonia.

Competitive adsorption of gaseous aromatic hydrocarbons in a binary mixture on nanoporous covalent organic polymers at various partial pressures

Covalent-organic polymers (COPs) are recognized for their great potential for treating diverse pollutants via adsorption. In this study, the sorption behavior of benzene and toluene was investigated both individually and in a binary mixture against two types of COPs possessing different -NH₂ functionalities. Namely, the potential of COPs was tested against benzene and toluene in a low inlet partial pressure range (0.5-20 Pa) using carbonyl-incorporated aromatic polymer (CBAP)-1-based diethylenediamine (EDA) [CD] and ethylenetriamine (DETA) [CE]. The maximum adsorption capacity and breakthrough values of both COPs showed dynamic changes with increases in the partial pressures of benzene and toluene. The maximum adsorption capacities (A_max) of benzene (as the sole component in N₂ under atmospheric conditions) on CD and CE were in the range of 24-36 and 33-75 mg g^-1, respectively. In contrast, with benzene and toluene in a binary mixture, the benzene A_max decreased more than two-fold (range of 2.7-15 and 6-39 mg g^-1, respectively) due to competition with toluene for sorption sites. In contrast, the toluene A_max values remained consistent, reflecting its competitive dominance over benzene. The adsorption behavior of the targeted compounds (i.e., benzene and toluene) was explained by fitting the adsorption data by diverse isotherm models (e.g., Langmuir, Freundlich, Elovich, and Dubinin-Radushkevich). The current research would be helpful for acquiring a better understanding of the factors affecting competitive adsorption between different VOCs in relation to a given sorbent and across varying partial pressures.