Formation Of Secondary Pollutants Research Articles

Atmospheric oxidation capacity and its contribution tosecondary pollutants formation

<p indent="0mm">Atmospheric oxidation capacity (AOC) is defined as the oxidation reaction rates of primary pollutants in the atmospheric chemical process, which is characterized by the oxidants concentration or the reaction rates. Atmospheric oxidation plays an important role in the formation of secondary pollutants, and works as an important indicator for the study of secondary pollution. Since 2013, the Chinese Government implemented unprecedented strident regulations to improve air quality. Although the overall levels of fine particulate matter (PM_2.5) have dropped considerably throughout China, it remains unclear how secondary pollutants have responded to the emission reductions in view of complex gas-precursor relationship and gas-particle interactions. Previous studies also reported the positive correlation between the AOC level and secondary pollutant concentrations. The updated Community Multi-scale Air Quality (CMAQ) model with the SAPRC 11 photo-chemical mechanism as well as the observation data was applied in this study to investigate the relationship of the secondary pollutants (ozone and secondary aerosols) and their precursors with the major oxidants (HO₂, OH and NO₃ radicals) in years 2013 and 2020 in China. And the process analysis tool was implemented in the CMAQ model to determine the key oxidants budget, which could better understand the primary sources and sinks of these oxidants. This analysis was able to calculate the chemical reaction rates at each integration time step. Radical source reactions were generally photolysis reactions, and the sink reactions removed radicals through the formation of stable products. The anthropogenic emissions were from Multiresolution Emission Inventory for China (MEIC) database, and the biogenic emissions were calculated from the Model of Emissions of Gas and Aerosols from Nature (MEGAN). The meteorology inputs were generated from the Weather Research and Forecasting (WRF) model. The CMAQ model predictions agree well with the observations, with most of the model performance within the criteria. The results show that the AOC level keeps identical from 2013 to 2020 throughout China. In the North China Plain (NCP) and the Pearl River Delta (PRD), the slightly increasing trends of AOC are even reported, which may aggravate the secondary pollution. The enhanced AOC level in the NCP is mainly from the reduced PM_2.5 concentration, which is regarded as the important sink of AOC. In addition, the concentration of major oxidants also represents different regional characteristics. The highest concentrations of HO_{<italic>x</italic>} and NO₃ radical are reported in the Sichuan Basin (SCB) and NCP, respectively. The ozone photolysis and the formation of HNO₃ (OH+NO₂) are reported as the most important AOC primary sources and sinks, respectively. In the NCP, the HONO photolysis is found as an important AOC source, which is consistent with previous studies. The AOC level increases significantly during the high ozone episode (increasing rate up to 475%). Also, the high level of AOC is corresponding to the significant increase of the secondary organic aerosols, indicating its important role in the formation of secondary pollutants. In summer, the reduction of NO_{<italic>x</italic>} emissions can reduce the AOC level. Meanwhile, a more complex response between the NO_{<italic>x</italic>} emissions and AOC level is found in winter. More rational emission reduction ratio of NO_{<italic>x</italic>} and volatile organic compounds (VOCs) should be applied to better control the AOC in China. In the future, more effective AOC control strategies should be established to reduce the PM_2.5 and O₃ coordinately in the 14th Five-Year Plan of China.

Emissions and Secondary Formation of Air Pollutants from Modern Heavy-Duty Trucks in Real-World Traffic-Chemical Characteristics Using On-Line Mass Spectrometry.

Complying with stricter emissions standards, a new generation of heavy-duty trucks (HDTs) has gradually increased its market share and now accounts for a large percentage of on-road mileage. The potential to improve air quality depends on an actual reduction in both emissions and subsequent formation of secondary pollutants. In this study, the emissions in real-world traffic from Euro VI-compliant HDTs were compared to those from older classes, represented by Euro V, using high-resolution time-of-flight chemical ionization mass spectrometry. Gas-phase primary emissions of several hundred species were observed for 70 HDTs. Furthermore, the particle phase and secondary pollutant formation (gas and particle phase) were evaluated for a number of HDTs. The reduction in primary emission factors (EFs) was evident (∼90%) and in line with a reduction of 28–97% for the typical regulated pollutants. Secondary production of most gas- and particle-phase compounds, for example, nitric acid, organic acids, and carbonyls, after photochemical aging in an oxidation flow reactor exceeded the primary emissions (EFAged/EFFresh ratio ≥2). Byproducts from urea-selective catalytic reduction systems had both primary and secondary sources. A non-negative matrix factorization analysis highlighted the issue of vehicle maintenance as a remaining concern. However, the adoption of Euro VI has a significant positive effect on emissions in real-world traffic and should be considered in, for example, urban air quality assessments.

Modeling sensitivities of BVOCs to different versions of MEGAN emission schemes in WRF-Chem (v3.6) and its impacts over eastern China

Abstract. Biogenic volatile organic compounds (BVOCs) simulated by current air quality and climate models still have large uncertainties, which can influence atmospheric chemistry and secondary pollutant formation. These modeling sensitivities are primarily due to two sources. One originates from different treatments in the physical and chemical processes associated with the emission rates of BVOCs. The other is errors in the specification of vegetation types and their distribution over a specific region. In this study, the version of the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) updated by the University of Science and Technology of China (USTC version of WRF-Chem) from the public WRF-Chem(v3.6) is used. The modeling results over eastern China with different versions (v1.0, v2.0, v3.0) of the Model of Emissions of Gases and Aerosols from Nature (MEGAN) in WRF-Chem are examined or documented. Sensitivity experiments with these three versions of MEGAN and two vegetation datasets are conducted to investigate the difference of three MEGAN versions in modeling BVOCs and its dependence on the vegetation distributions. The experiments are also conducted for spring (April) and summer (July) to examine the seasonality of the modeling results. The results indicate that MEGAN v3.0 simulates the largest amount of biogenic isoprene emissions over eastern China. The different performance among MEGAN versions is primarily due to their different treatments of applying emission factors and vegetation types. In particular, the results highlight the importance of considering the sub-grid vegetation fraction in estimating BVOC emissions over eastern China, which has a large area of urbanization. Among all activity factors, the temperature-dependent factor dominates the seasonal change of activity factor in all three versions of MEGAN, while the different response to the leaf area index (LAI) change determines the difference among the three versions in seasonal variation of BVOC emissions. The simulated surface ozone concentration due to BVOCs can be significantly different (ranging from 1 to more than 10 ppbv in some regions) among the experiments with three versions of MEGAN, which is mainly due to their impacts on surface VOCs and NOx concentrations. Theoretically MEGAN v3.0 that is coupled with the land surface scheme and considers the sub-grid vegetation effect should overcome previous versions of MEGAN in WRF-Chem. However, considering uncertainties of retrievals and anthropogenic emissions over eastern China, it is still difficult to apply satellite retrievals of formaldehyde and/or limited sparse in situ observations to constrain the uncertain parameters or functions in BVOC emission schemes and their impacts on photochemistry and ozone production. More accurate vegetation distribution and measurements of biogenic emission fluxes and species concentrations are still needed to better evaluate and optimize models.

RTEII: A new high-resolution (0.1° × 0.1°) road transport emission inventory for India of 74 speciated NMVOCs, CO, NOx, NH3, CH4, CO2, PM2.5 reveals massive overestimation of NOx and CO and missing nitromethane emissions by existing inventories

21 of 30 most polluted cities for particulate matter (PM 2.5 ) are in India, yet the distribution, identity and emissions of volatile organic compounds (VOCs) from traffic, which are PM 2.5 and ozone precursors, remain unknown. Here, we measured emission factors (EFs) of 74 VOCs from a range of Indian vehicle-technology and fuel types. When combined with 0.1 ° × 0.1 ° spatially resolved activity data for the year 2015, toluene (137 ± 39 Gg yr 1 ), isopentane (111 ± 38 Ggyr −1 ), and acetaldehyde (41 ± 6 Ggyr −1 ) were top 3-VOC emissions. Petrol-2-wheelers and LPG-3-wheelers emitted the highest VOCs (EFs> 50 gVOC/L) and had highest secondary pollutant formation potential, so their replacement with electric vehicles would improve air quality. EDGARv4.3.2 and REASv.2.1 emission inventories overestimated total road sector emitted VOCs due to obsolete EFs and activity data, in particular over-estimating ethene, propene, ethyl benzene, 2,2- dimethyl butane, CO, NO x while significantly under-estimating acetaldehyde. Nitromethane emissions were missing from previous inventories and with isocyanic acid and benzene contributed significantly to toxic emissions (summed total ~41 ± 4 Ggyr −1 ). Knowledge of key VOCs emitted from the world's third largest road-network provides critical new data for mitigating secondary pollutant formation over India and will enable more accurate modelling of atmospheric composition over South Asia. • Emission factors of 74 VOCs measured for Indian vehicular categories including LPG and CNG vehicles reveal high acetaldehyde. • 0.1 × 0.1° speciated VOC traffic emission inventory over India with updated activity data shows overestimate by inventories. • Petrol 2-wheelers and LPG 3-wheelers had highest pollutant emissions.

Probing wintertime air pollution sources in the Indo-Gangetic Plain through 52 hydrocarbons measured rarely at Delhi & Mohali

During wintertime, the Indo-Gangetic Plain suffers from severe air pollution affecting several hundred million people. Here we present unprecedented measurements and source analyses of 52 NMHCs (25 alkanes, 16 aromatics, 10 alkenes and one alkyne) in the cities of Delhi and Mohali (300 km north of Delhi) during wintertime (Dec 2016–Jan 2017). NMHCs were measured using a thermal desorption gas chromatograph equipped with flame ionisation detectors with data traceable to WMO standards. The ten most abundant NMHCs that were measured were the same at both Delhi and Mohali: propane, n-butane, acetylene, ethane, toluene, i-butane, ethene, i-pentane, benzene and propene and accounted for >50% of total measured NMHC mass concentration (137 ± 5.8 μg m−3 in Mohali and 239 ± 7.7 μg m−3 in Delhi). Ambient NMHCs and calculated hydroxyl radical reactivity were approximately twice as high in Delhi relative to Mohali, and 2–12 times higher than most other mega-cities, except Lahore and Karachi. Using chemical source signatures, traffic and LPG usage emissions were identified as the major contributor of these reactive NMHCs at both sites during nighttime, with additional minor contributions of garbage burning in Mohali, and evaporative fuel and biomass burning emissions in Delhi. Comparison of NMHC/CO and NMHC/C2H2 ratios over Mohali and Delhi, to other cities, suggested gasoline/petrol-fuelled vehicles were major NMHC emitters within the traffic source. The data from both Mohali and Delhi suggest that a large fraction of the fleet comprised vehicles with older emission control in both Mohali and Delhi. Analyses revealed poor representation of propene, ethene and trimethylbenzenes in the emission inventory (EDGARv4.3.2) over Mohali and Delhi. This study provides key data and new insights into the sources of reactive NMHCs (lifetime < few days) that drive regional wintertime pollution through direct effects and the formation of secondary pollutants.

Local emissions and secondary pollutants cause severe PM2.5 elevation in urban air at the south edge of the North China Plain: Results from winter haze of 2017–2018 at a mega city

Severe haze occurrence in the north of the North China Plain (NCP) is recognized as a consequence of the regional transport of pollutants initially from the south and then the rapid formation of secondary pollutants in the local air. However, the origin of pollutants causing haze in the southern NCP has not yet been elucidated even through careful data observation. Based on the contents of water-soluble inorganic ions in PM2.5 samples collected during two severe haze episodes in Zhengzhou, a mega city located on the southern edge of the NCP, we estimated the contributions of local primary emissions and secondary pollutants to haze occurrence. On average, Na+, K+, and Ca2+ mainly originated from anthropogenic sources, and their anthropogenic fractions had proportions of 97.5%, 93.9%, and 76.5% in their respective total mass. Anions Cl− and SO42− substantially originated from not only produced substantially via secondary formation but also from primary emissions, and their primary proportions in their respective total mass were 51.1% and 30.8%. In contrast, NH4+ and NO3− were dominated by secondary formation. The increase in PM2.5 was mainly caused by the formation of secondary inorganic (29.1%) and organic species (57.2%) and the primary anthropogenic emissions (12.5%). These results indicated that the haze at the southern edge of the NCP was mainly caused by pollutants in the local areas. Compared to the haze in the northern NCP, the haze in the southern NCP edge had a higher PM2.5 mass concentration and a higher proportion of secondary species, but a lower proportion of primary species, indicating the high heterogeneity of winter haze over the NCP.

Characterizing nitrate radical budget trends in Beijing during 2013–2019

Nitrate (NO3) radical is an important oxidant in the atmosphere as it regulates the NOx budget and impacts secondary pollutant formation. Here, a long-term observational dataset of NO3-related species at an urban site in Beijing was used to investigate changes in the NO3 budget and their atmospheric impacts during 2013–2019, in this period the Clean Air Actions Plan was carried out in China. We found that (1) changes in NO3 precursors (NO2 and O3) led to a significant increase in NO3 formation in the surface layer in winter but a decrease in summer; (2) a reduction in NOx promoted thermal equilibrium, favoring the formation of NO3 rather than dinitrogen pentoxide (N2O5). The simultaneous decrease in PM2.5, during these years, further weakened the N2O5 heterogeneous uptake; (3) a box model simulation revealed that both the reactions of NO3 with volatile organic compounds (VOC) and N2O5 uptake were weakened in summer, implying that the policy actions implemented help to moderate secondary aerosol formation caused by NO3 and N2O5 chemistry in summer; and (4) during winter, both NO3 + VOC and N2O5 uptake were enhanced. Specifically, for the N2O5 uptake, the rapid increase in NO3 production, or to some extent, NO3 oxidation capacity, far outweighed the negative shift effect, leading to a net enhancement of N2O5 uptake in winter, which indicates that the action policy implemented led to an adverse effect on particulate nitrate formation via N2O5 uptake in winter. This may explain the persistent winter particulate nitrate pollution in recent years. Our results highlight the systematic changes in the NO3 budget between 2013 and 2019 in Beijing, which subsequently affect secondary aerosol formation in different seasons.

Progress on the vertical observation methods of volatile organic compounds and their applications within the atmospheric boundary layer

<p indent="0mm">Volatile organic compounds (VOCs) are important trace gases in the troposphere that play vital roles in the formation of secondary air pollutants such as ozone and organic aerosol components. An in-depth characterization of the spatiotemporal variability, particularly in three-dimensions, of VOCs in the atmospheric boundary layer is an essential prerequisite for understanding the formation mechanisms of regional pollution episodes. However, vertically resolved VOCs measurements are seldom made during field campaigns due to the limitation of available observation techniques. This review summarizes the progress in vertical observation of VOCs and their applications to the atmospheric boundary layer, focusing on the introduction of platforms for vertical measurement techniques for VOCs, including high-rise buildings, tethered balloons, aircraft, unmanned aerial vehicles (UAVs), and remote sensing. All of these platforms have been used in previous studies and have their respective advantages and disadvantages. High-rise buildings are generally characterized by low altitudes and fixed locations but could serve as long-term platforms for both online and offline VOCs measurements. Tethered balloons, generally used for offline VOCs measurements, have flexible launch locations and altitude ranges. Aircraft can provide platforms for both offline and online VOCs measurements over large spatial scales, but aircrafts are not suitable for long-term observations because of their high operating cost. Similar to tethered balloons, UAVs are used for offline VOCs measurements, while they are much more flexible in utilization and can be launched in complex environments. However, small payload, short flight duration, and availability of airspace are key factors that limit the wide application of UAVs in the field of environmental monitoring. Remote sensing platforms (including ground-based and space-based techniques) could provide vertical measurements of several VOCs species over large temporal and spatial scales. However, the vertical VOCs profiles provided by remote sensing techniques are frequently characterized by large uncertainty. With the rapid development of VOCs measurement techniques (such as UAVs and proton-transfer-reaction time-of-flight mass spectrometry), future studies are expected to obtain vertical VOCs observations with higher spatiotemporal resolutions as well as lower operating costs. Vertical observations of VOCs concentrations could provide valuable opportunities for a thorough analysis of VOCs emissions and variation of their related chemical processes within the atmospheric boundary layer. Therefore, this review also summarizes the progress in applications of vertical VOCs observations in the atmospheric boundary layer, focusing on introducing the key factors influencing VOCs vertical distribution patterns, determination of VOCs emission fluxes, evaluation and calibration of VOCs emission inventories, investigation of the vertical distribution of photochemical ozone production sensitivity, and the vertical distribution of VOCs degradation mechanisms at night. At present, vertical observations are predominantly used to identify impacts of transport and boundary-layer dynamics on the vertical distributions of different VOCs species and to estimate speciated VOCs emissions. However, the vertical variability of the oxidation and degradation mechanisms for different VOCs species and the environmental effects of this variability have been reported in only a few studies. More effort should be made to elucidate how the interactions between VOCs chemistry and vertical transport affect the formation and concentration of secondary air pollutants at ground level. In summary, there is an urgent need to obtain reliable vertical observations of key VOCs species in the atmospheric boundary layer for better investigating the formation mechanisms of regional atmospheric pollution.

Improvement in Modeling of OH and HO2 Radical Concentrations during Toluene and Xylene Oxidation with RACM2 Using MCM/GECKO-A

Due to their major role in atmospheric chemistry and secondary pollutant formation such as ozone or secondary organic aerosols, an accurate representation of OH and HO2 (HOX) radicals in air quality models is essential. Air quality models use simplified mechanisms to represent atmospheric chemistry and interactions between HOX and organic compounds. In this work, HOX concentrations during the oxidation of toluene and xylene within the Regional Atmospheric Chemistry Mechanism (RACM2) are improved using a deterministic–near-explicit mechanism based on the Master Chemical Mechanism (MCM) and the generator of explicit chemistry and kinetics of organics in the atmosphere (GECKO-A). Flow tube toluene oxidation experiments are first simulated with RACM2 and MCM/GECKO-A. RACM2, which is a simplified mechanism, is then modified to better reproduce the HOX concentration evolution simulated by MCM/GECKO-A. In total, 12 reactions of the oxidation mechanism of toluene and xylene are updated, making OH simulated by RACM2 up to 70% more comparable to the comprehensive MCM/GECKO-A model for chamber oxidation simulations.

Explicit modeling of isoprene chemical processing in polluted air masses in suburban areas of the Yangtze River Delta region: radical cycling and formation of ozone and formaldehyde

Abstract. In recent years, ozone pollution has become one of the most severe environmental problems in China. Evidence from observations have showed increased frequency of high O3 levels in suburban areas of the Yangtze River Delta (YRD) region. To better understand the formation mechanism of local O3 pollution and investigate the potential role of isoprene chemistry in the budgets of ROx (OH+HO2+RO2) radicals, synchronous observations of volatile organic compounds (VOCs), formaldehyde (HCHO), and meteorological parameters were conducted at a suburban site of the YRD region in 2018. Five episodes with elevated O3 concentrations under stagnant meteorological conditions were identified; an observation-based model (OBM) with the Master Chemical Mechanism was applied to analyze the photochemical processes during these high O3 episodes. The high levels of O3, nitrogen oxides (NOx), and VOCs facilitated strong production and recycling of ROx radicals with the photolysis of oxygenated VOCs (OVOCs) being the primary source. Our results suggest that local biogenic isoprene is important in suburban photochemical processes. Removing isoprene could drastically slow down the efficiency of ROx recycling and reduce the concentrations of ROx. In addition, the absence of isoprene chemistry could further lead to a decrease in the daily average concentrations of O3 and HCHO by 34 % and 36 %, respectively. Therefore, this study emphasizes the importance of isoprene chemistry in the suburban atmosphere, particularly with the participation of anthropogenic NOx. Moreover, our results provide insights into the radical chemistry that essentially drives the formation of secondary pollutants (e.g., O3 and HCHO) in suburban areas of the YRD region.

Characteristics and Cause Analysis of Heavy Air Pollution in a Mountainous City During Winter

Taking the typical heavy air pollution process in Yangquan from December 26, 2018 to January 20, 2019 as an example, the characteristics and cause analysis of heavy air pollution in a mountainous city in winter were analyzed in this study. The results showed that fine particle mass (PM2.5) was the primary pollutant during the heavy pollution period. The water-soluble ions and carbonaceous components were the main components of PM2.5. The secondary ions of SO42-, NO3-, and NH4+ had the lager contribution to water-soluble ions (87.7%), and the secondary organic carbon (SOC) was the main component of the carbonaceous components (71.6%). The concentration of the secondary ions during the heavy pollution period increased by 5.3 times compared to levels before the heavy pollution period, and was an important component resulting in the fast increase of PM2.5. An analysis of meteorological conditions showed that PM2.5 and its main components had a significantly positive relationship with humidity and a significantly negative relationship with wind speed. And that pollution became stronger with an increase in humidity and a decrease in wind speed. The typical meteorological characteristics of mountainous cities are high relative humidity and large temperature variations, which can accelerate the formation of secondary pollutants and are the main reasons for the rapid aggravation of PM2.5. In addition, the lower average wind speed caused by the relatively closed terrain in mountainous cities makes the diffusion conditions of air pollutants relatively poor, which is one of the reasons for the accumulation of pollutants. The source apportionment results showed that the secondary sources (46.0%) were the most important source of PM2.5, followed by coal combustion (32.6%), vehicle exhaust (19.8%), and fugitive dust (1.6%). Therefore, mountainous cities should pay more attention to controlling secondary components, especially secondary ions.

Characterization of a chemical modulation reactor (CMR) for the measurement of atmospheric concentrations of hydroxyl radicals with a laser-induced fluorescence instrument

Abstract. Precise and accurate hydroxyl radical (OH) measurements are essential to investigate mechanisms for oxidation and transformation of trace gases and processes leading to the formation of secondary pollutants like ozone (O3) in the troposphere. Laser-induced fluorescence (LIF) is a widely used technique for the measurement of ambient OH radicals and was used for the majority of field campaigns and chamber experiments. Recently, most LIF instruments in use for atmospheric measurements of OH radicals introduced chemical modulation to separate the ambient OH radical concentration from possible interferences by chemically removing ambient OH radicals before they enter the detection cell (Mao et al., 2012; Novelli et al., 2014a). In this study, we describe the application and characterization of a chemical modulation reactor (CMR) applied to the Forschungszentrum Jülich LIF (FZJ-LIF) instrument in use at the atmospheric simulation chamber SAPHIR (Simulation of Atmospheric PHotochemistry In a large Reaction Chamber). Besides dedicated experiments in synthetic air, the new technique was extensively tested during the year-round Jülich Atmospheric Chemistry Project (JULIAC) campaign, in which ambient air was continuously flowed into the SAPHIR chamber. It allowed for performing OH measurement comparisons with differential optical absorption spectroscopy (DOAS) and investigation of interferences in a large variety of chemical and meteorological conditions. Good agreement was obtained in the LIF–DOAS intercomparison within instrumental accuracies (18 % for LIF and 6.5 % for DOAS) which confirms that the new chemical modulation system of the FZJ-LIF instrument is suitable for measurement of interference-free OH concentrations under the conditions of the JULIAC campaign (rural environment). Known interferences from O3+H2O and the nitrate radical (NO3) were quantified with the CMR in synthetic air in the chamber and found to be 3.0×105 and 0.6×105 cm−3, respectively, for typical ambient-air conditions (O3=50 ppbv, H2O = 1 % and NO3=10 pptv). The interferences measured in ambient air during the JULIAC campaign in the summer season showed a median diurnal variation with a median maximum value of 0.9×106 cm−3 during daytime and a median minimum value of 0.4×106 cm−3 at night. The highest interference of 2×106 cm−3 occurred in a heat wave from 22 to 29 August, when the air temperature and ozone increased to 40 ∘C and 100 ppbv, respectively. All observed interferences could be fully explained by the known O3+H2O interference, which is routinely corrected in FZJ-LIF measurements when no chemical modulation is applied. No evidence for an unexplained interference was found during the JULIAC campaign. A chemical model of the CMR was developed and applied to estimate the possible perturbation of the OH transmission and scavenging efficiency by reactive atmospheric trace gases. These can remove OH by gas phase reactions in the CMR or produce OH by non-photolytic reactions, most importantly by the reaction of ambient HO2 with NO. The interfering processes become relevant at high atmospheric OH reactivities. For the conditions of the JULIAC campaign with OH reactivities below 20 s−1, the influence on the determination of ambient OH concentrations was small (on average: 2 %). However, in environments with high OH reactivities, such as in a rain forest or megacity, the expected perturbation in the currently used chemical modulation reactor could be large (more than a factor of 2). Such perturbations need to be carefully investigated and corrected for the proper evaluation of OH concentrations when applying chemical scavenging. This implies that chemical modulation, which was developed to eliminate interferences in ambient OH measurements, itself can be subject to interferences that depend on ambient atmospheric conditions.

Non-methane hydrocarbons in the vicinity of a petrochemical complex in the Metropolitan Area of São Paulo, Brazil

Volatile organic compounds (VOCs) are fundamental in the atmospheric reactions, producing tropospheric ozone (O3) and secondary organic aerosols (SOA). We evaluated the hydrocarbons (HCs) near a petrochemical and industrial complex (PIC) in the metropolitan area of Sao Paulo (MASP). Air samples were hourly collected in two different sites during different days, 2016–2017. The most abundant compounds were toluene (1.5 ± 1.1 ppbv), cis-2-hexene (1.4 ± 1.9 ppbv), benzene (0.55 ± 0.66 ppbv), and m+p-xylene (0.58 ± 0.3 ppbv). HC concentrations observed at the BTP site (industrial) were approximately two times higher than those at the UFABC site (traffic). The aromatics presented the highest contribution at BTP (58%) and UFABC (56%). In addition, our comparison with other industrial areas worldwide showed a good agreement in the HC profile with Japan and the USA, suggesting the presence of similar emission sources. BTEX (benzene, toluene, ethylbenzene, m+p- and o-xylenes) correlations and ratios showed that despite vehicular emissions were the main sources of these compounds around PIC, there is the influence from industrial sources among others. Finally, to evaluate the potential impacts associated to PIC emissions, the formation of secondary pollutants was analyzed. Aromatic compounds represented ~98% and ~68% of the total SOA and O3 formation estimation, respectively. The lifetime cancer risk (LCR) for benzene was 5.75 × 10−6 and 4.25 × 10−6 for BTP and UFABC, respectively, which exceeds the US EPA recommendation (<1 × 10−6) and could negatively affect the populations health in this region

Microbial Enzymes Used in Bioremediation

Emerging pollutants in nature are linked to various acute and chronic detriments in biotic components and subsequently deteriorate the ecosystem with serious hazards. Conventional methods for removing pollutants are not efficient; instead, they end up with the formation of secondary pollutants. Significant destructive impacts of pollutants are perinatal disorders, mortality, respiratory disorders, allergy, cancer, cardiovascular and mental disorders, and other harmful effects. The pollutant substrate can recognize different microbial enzymes at optimum conditions (temperature/pH/contact time/concentration) to efficiently transform them into other rather unharmful products. The most representative enzymes involved in bioremediation include cytochrome P450s, laccases, hydrolases, dehalogenases, dehydrogenases, proteases, and lipases, which have shown promising potential degradation of polymers, aromatic hydrocarbons, halogenated compounds, dyes, detergents, agrochemical compounds, etc. Such bioremediation is favored by various mechanisms such as oxidation, reduction, elimination, and ring-opening. The significant degradation of pollutants can be upgraded utilizing genetically engineered microorganisms that produce many recombinant enzymes through eco-friendly new technology. So far, few microbial enzymes have been exploited, and vast microbial diversity is still unexplored. This review would also be useful for further research to enhance the efficiency of degradation of xenobiotic pollutants, including agrochemical, microplastic, polyhalogenated compounds, and other hydrocarbons.

Impact of the COVID-19 pandemic on air pollution in Chinese megacities from the perspective of traffic volume and meteorological factors

During 2020, the COVID-19 pandemic resulted in a widespread lockdown in many cities in China. In this study, we assessed the impact of changes in human activities on air quality during the COVID-19 pandemic by determining the relationships between air quality, traffic volume, and meteorological conditions. The megacities of Wuhan, Beijing, Shanghai, and Guangzhou were selected as the study area, and the variation trends of air pollutants for the period January–May between 2016 and 2020 were analyzed. The passenger volume of public transportation (PVPT) and the passenger volume of taxis (PVT) along with data on precipitation, temperature, relative humidity, wind speed, and boundary layer height were used to identify and quantify the driving force of the air pollution variation. The results showed that the change rates of fine particulate matter (PM2.5), NO2, and SO2 before and during the lockdown in the four megacities ranged from −49.9% to 78.2% (average: −9.4% ± 59.3%), −55.4% to −32.3% (average: −43.0% ± 9.7%), and − 21.1% to 11.9% (average: −10.9% ± 15.4%), respectively. The response of NO2 to the lockdown was the most sensitive, while the response of PM2.5 was smaller and more delayed. During the lockdown period, haze from uninterrupted industrial emissions and fireworks under the effect of air mass transport from surrounding areas and adverse climate conditions was probably the cause of abnormally high PM2.5 concentrations in Beijing. In addition, the PVT was the most significant factor for NO2, and meteorology had a greater impact on PM2.5 than NO2 and SO2. There is a need for more national-level policies for limiting firework displays and traffic emissions, as well as further studies on the formation and transmission of secondary air pollutants.

Nanozeolites from thermoelectric waste for application to wastewater treatment: review

Along the years, nanozeolites have been proved extremely efficient in wastewater treatment. These nanostructured materials have a series of applications such as nanoadsorption, nanocatalysts to heterogenous photocatalyst, membrane separation processes and Fenton-like, showing a good removal of inorganic and organic pollutants. However, conventional synthesis of nanozeolite have some limitations, such as the formation of secondary pollutants by using organic supports or prolonged reaction times. In this context, the present work aims to provide an overview about the application of nanozeolites from coal fly ash in wastewater treatment. For this purpose, Science Direct platform was used, with the descriptors “Zeolite” AND “fly ash” AND “organic pollutants” AND “wastewater”, according to Boolean logic, and limiting to the last 5 years (from January 2015 to September 2020). Then, 22 articles were found being 70% of these studies corresponding to the nanoadsorption technology, 15% to Fenton-like treatment, 10% membrane separation processes, and only 5% to application in heterogenous photocatalysis, like supported catalysts. Therefore, it is possible to identify a wide application of these materials for application in wastewater treatment, being a potential alternative to green nanotechnology with sustainable development.

Nitrogen Oxide Soil Emission Measurements Using Passive Samplers and Static Chamber Method

Nitrogen oxides play a major role in atmospheric chemistry, like primary pollutants, in the formation of secondary air pollutants or greenhouse gases (GHGs). This research study was conducted in the Western Pannonian sub-region of Croatia with the aim to determine the suitability of our internally developed passive sampler and static chamber method for N-NO2 concentration measurement. The aim was also to determine the impact of mineral soil fertilization on the N-NO2 flux during triticale vegetation. The research showed that the method used was suitable. Average daily N-NO2 flux ranged from 2.78 to 5.09 mg ha–1 day–1 depending on phenophase and treatment. Statistically significant differences in N-NO2 flux between two monitored treatments (300 kg N ha–1 and 0 kg N ha–1) were not observed, nor between two investigated phenophases.

Magnetic Hydroxyapatite for Batch Adsorption of Heavy Metals

In this work, magnetic hydroxyapatite or hydroxyapatite-iron (III) oxide (HAp-Fe3O4) composite was used as the adsorbent of heavy metals and the performance was evaluated using the batch test. The presence of heavy metals in the effluent from wastewater discharge can be toxic to many organisms and can even lead to eye burns. Therefore, hydroxyapatite synthesized from the chemical precipitation of calcium nitrate tetrahydrate and diammonium hydrogen phosphate solutions is used to remove heavy metal in aqueous media. Magnetic properties of Fe3O4 can help prevent formation of secondary pollutants caused by the loss of adsorbent. The synthesized HAp-Fe3O4 can remove cadmium, zinc and lead effectively, which is up to 90% removal. Reusability study shows that the adsorbent could retain heavy metal ions even after four cycles. The percentage removal of heavy metals maintains at around 80% after four times of usage. The composite of HAp-Fe3O4 demonstrates good performance and stability which is beneficial for heavy metal removal in the future.

Simulation of primary and secondary particles in the streets of Paris using MUNICH.

High particle concentrations are observed in the streets. Regional-scale chemistry-transport models are not able to reproduce these high concentrations, because their spatial resolution is not fine enough. Local-scale models are usually employed to simulate the high concentrations in street networks, but they often adopt substantial simplifications to determine background concentrations and use simplified chemistry. This study presents the new version of the local-scale Model of Urban Network of Intersecting Canyons and Highways (MUNICH) that integrates background concentrations simulated by the regional-scale chemistry-transport model Polair3D, and uses the same complex chemistry module as Polair3D, SSH-aerosol, to represent secondary aerosol formation. Gas and aerosol concentrations in Paris streets are simulated with MUNICH, considering a street-network with more than 3800 street segments, between 3 May and 30 June. Comparisons with PM10 and PM2.5 measurements at several locations of Paris show that the high PM10 and PM2.5 concentrations are well represented. Furthermore, the simulated chemical composition of fine particles corresponds well to a yearly measured composition. To understand the influence of the secondary pollutant formation, several sensitivity simulations are conducted. Simulations with and without gas-phase chemistry show that the influence of gas-phase chemistry on the formation of NO2 is large (37% on average over May and across all modelled streets), but the influence on condensables is lower (less than 2% to 3% on average at noon for inorganics and organics), but may reach more than 20% depending on the street. The assumption used to compute gas/particle mass transfer by condensation/evaporation is important for inorganic and organic compounds of particles, as using the thermodynamic equilibrium assumption leads to an overestimation of the organic concentrations by 4.7% on average (up to 31% at noon depending on the streets). Ammonia emissions from traffic lead to an increase in inorganic concentrations by 3% on average, reaching 26% depending on the street segments. Not taking into account gas-phase chemistry and aerosol dynamics in the modelling leads to an underestimation of organic concentrations by about 11% on average over the streets and time, but this underestimation may reach 51% depending on the streets and the time of the day.

Impacts of chlorine emissions on secondary pollutants in China

The identified components of fine particulate matter with dynamic diameters less than 2.5 μm (PM2.5) suggests the remarkable increase in Cl− in PM2.5 during autumn and winter over North China. Anthropogenic chlorine emissions, including those from biomass burning, coal combustion and biofuel burning, are the main sources of Cl−, which could potentially affect the formation of secondary pollutants in the troposphere. In this study, we resolve the effect of chlorine emissions on PM2.5 and O3 by using the Weather Research and Forecasting (WRF) model coupled with Chemistry (WRF-Chem model) with an updated chemistry mechanism that includes the gaseous chemistry of chlorine, N2O5 heterogeneous reactions and detailed aqueous chemistry. Additionally, the biomass burning emissions of chlorine are derived from the Fire Inventory of the National Center for Atmospheric Research (NCAR) (FINN), which are considered the main contributor to atmospheric chloride over inland areas. The improved model is able to simulate the atmospheric Cl− in PM2.5 with reasonable agreement with the available observations in China. In addition, this model reduces the mean bias of ground-level PM2.5 concentrations from −7.5% to 3.2% over the BTH area and from −11.6% to −0.4% over the Northeast China Plain (NEP). The model also slightly improves O3 simulations by reducing the mean bias from 25.3% to 23.9% over mainland China. The anthropogenic chlorine emissions are estimated to increase the monthly average PM2.5 by 7.5 μg/m3 (9.1%), whereas ozone decreases slightly by up to 2.1 ppbv (4.3%) in November 2014. The influence of ozone was more significant in summer, reaching 2–8 ppbv over the biomass burning regions in 2014. The increase in Cl− and NH4+ accounted for the impacts on PM2.5, and the decline in O3 could be explained by the cycle between chlorine radicals and gases and changes in precursor concentrations. Our results suggest the importance of chlorine emissions and their chemical processes in the formation of PM2.5 and O3 over high-emission regions in China.