Search Results (22)

Atmospheric aqueous-phase reactions have been recognized as an important source of secondary organic aerosols (SOAs). However, the unclear reaction kinetics and mechanics hinder the in-depth understanding of the SOA sources and formation processes. This study selected ten different substituted phenolic compounds (termed as PhCs) emitted from biomass burning as precursors, to investigate the kinetics using OH oxidation reactions under simulated sunlight. The factors influencing reaction rates were examined, and the contribution of reactive oxygen species (ROS) was evaluated through quenching and kinetic analysis experiments. The results showed that the pseudo-first-order rate constants (k_obs) for the OH oxidation of phenolic compounds ranged from 1.03 × 10⁻⁴ to 7.85 × 10⁻⁴ s⁻¹ under simulated sunlight irradiation with an initial H₂O₂ concentration of 3 mM. Precursors with electron-donating groups (-OH, -OCH₃, -CH₃, etc.) exhibited higher electrophilic radical reactivity due to the enhanced electron density of the benzene ring, leading to higher reaction rates than those with electron-withdrawing groups (-NO₂, -CHO, -COOH). At pH 2, the second-order reaction rate (k_{PhCs, OH}) was lower than at pH 5. However, the k_obs did not show dependence on pH. The presence of O₂ facilitated substituted phenols’ photodecay. Inorganic salts and transition metal ions exhibited varying effects on reaction rates. Specifically, NO₃⁻ and Cu²⁺ promoted k_{PhCs, OH}, Cl⁻ significantly enhanced the reaction at pH 2, while SO₄²⁻ inhibited the reaction. The k_{PhCs, OH} were determined to be in the range of 10⁹~10¹⁰ L mol⁻¹ s⁻¹ via the bimolecular rate method, and a modest relationship with their oxidation potential was found. Additionally, multiple substituents can suppress the reactivity of phenolic compounds toward •OH based on Hammett plots. Quenching experiments revealed that •OH played a dominant role in phenolic compound degradation (exceeding 65%). Electron paramagnetic resonance confirmed the generation of singlet oxygen (¹O₂) in the system, and probe-based quantification further explored the concentrations of •OH and ¹O₂ in the system. Based on reaction rates and concentrations, the atmospheric aqueous-phase lifetimes of phenolic compounds were estimated, providing valuable insights for expanding atmospheric kinetic databases and understanding the chemical transformation and persistence of phenolic substances in the atmosphere. Full article

Ammonia (NH₃) is an important precursor to airborne fine particulate matter (PM_2.5) which causes significant health issues and can significantly impact terrestrial and aquatic ecosystems through deposition. The largest source of NH₃ emissions in the UK is agriculture, including animal husbandry and NH₃-based fertilizer applications. This study investigates the impact of mitigation measures targeting UK NH₃ emissions from farming activities, focusing on their implications for air quality and nitrogen deposition in 2030. A series of mitigation scenarios—low2030, medium2030, and high2030—were developed through engagement with stakeholders, including farmers, advisers, and researchers, and their impact was modelled using the CMAQ air quality model. These scenarios represent varying levels of the uptake of mitigation measures compared to a baseline (base2030). The results indicate that reductions in total NH₃ emissions across the UK could reach up to 13% under the high2030 scenario (but reaching nearly 20% for some regions). These reductions can lead to significant decreases in NH₃ concentrations in some parts of the UK (up to 22%, ~1.2 µg/m³) but with a mean reduction of 8% across the UK. However, the reductions have a limited effect on fine ammonium particulate (${\mathrm{N}\mathrm{H}}_4^{+}$) concentrations, achieving only modest reductions of up to 4%, with mean reductions of 1.6–1.9% due to a NH₃-rich atmosphere. Consequently, the mitigation measures have minimal impact on secondary inorganic aerosol formation and PM_2.5 concentrations, aligning with findings from other studies in Europe and beyond. These results suggest that addressing the primary sources of PM_2.5 or other PM_2.5 precursors, either alone or in combination with NH₃, may be necessary for more substantial air quality improvements. In terms of nitrogen (N) deposition, reductions in NH₃ emissions primarily affect NH₃ dry deposition, which constitutes approximately two-thirds of reduced nitrogen deposition. Total N deposition declines by 15–18% in source regions depending on the scenario, but national average reductions remain modest (~4%). While the study emphasizes annual estimates, further analyses focusing on finer temporal scales (e.g., daily or seasonal) could provide additional insights into exposure impacts. This research highlights the need for integrated mitigation strategies addressing multiple pollutants to achieve meaningful reductions in air pollution and nitrogen deposition. Full article

Water-soluble inorganic ions (WSIIs) can increase the hygroscopicity of aerosols, which will transform aerosols into larger sizes and reduce visibility by enhancing light scattering. To explore the characteristics of WSII concentrations and their impacts on visibility in a coastal airport, in this study, PM_1.0 samples at two monitoring sites (including airport site and background site) were collect in spring and summer, and 12 species of ions were detected. In general, secondary water-soluble inorganic ions (SNA, including ${\mathrm{SO}}_4^{2-}$, ${\mathrm{NO}}_3^{-}$ and ${\mathrm{NH}}_4^{+}$) and ${\mathrm{Ca}}^{2+}$ were the dominant WSIIs in PM_1.0, contributing about 89% to 95% of the total measured ions. The continental contributions of ${\mathrm{SO}}_4^{2-}$, ${\mathrm{K}}^{+}$, and ${\mathrm{Ca}}^{2+}$ accounted for more than 60% during the whole period, while Na⁺ and ${\mathrm{Cl}}^{-}$ were mainly from marine sources. The source identification showed that airport emissions were a major source at the sampling site and significantly contributed to the levels of sulfate, nitrate, and ammonium. Agricultural activities were the dominant sources impacting visibility in spring, while airport emissions and secondary inorganic aerosols were the main components affecting visibility in summer. Therefore, improving atmospheric visibility in coastal airport areas should focus on reducing the precursors of secondary particulates and reducing biomass-burning activities. Full article

Despite significant improvements in air quality during and after COVID-19 restrictions, haze continued to occur in Zhengzhou afterwards. This paper compares ionic compositions and sources of PM_2.5 before (2019), during (2020), and after (2021) the restrictions to explore the reasons for the haze. The average concentration of PM_2.5 decreased by 28.5% in 2020 and 27.9% in 2021, respectively, from 102.49 μg m⁻³ in 2019. The concentration of secondary inorganic aerosols (SIAs) was 51.87 μg m⁻³ in 2019, which decreased by 3.1% in 2020 and 12.8% in 2021. In contrast, the contributions of SIAs to PM_2.5 increased from 50.61% (2019) to 68.6% (2020) and 61.2% (2021). SIAs contributed significantly to PM_2.5 levels in 2020–2021. Despite a 22~62% decline in NO_x levels in 2020–2021, the increased O₃ caused a similar NO₃⁻ concentration (20.69~23.00 μg m⁻³) in 2020–2021 to that (22.93 μg m⁻³) in 2019, hindering PM_2.5 reduction in Zhengzhou. Six PM_2.5 sources, including secondary inorganic aerosols, industrial emissions, coal combustion, biomass burning, soil dust, and traffic emissions, were identified by the positive matrix factorization model in 2019–2021. Compared to 2019, the reduction in PM_2.5 from the secondary aerosol source in 2020 and 2021 was small, and the contribution of secondary aerosol to PM_2.5 increased by 13.32% in 2020 and 12.94% in 2021. In comparison, the primary emissions, including biomass burning, traffic, and dust, were reduced by 29.71% in 2020 and 27.7% in 2021. The results indicated that the secondary production did not significantly contribute to the PM_2.5 decrease during and after the COVID-19 restrictions. Therefore, it is essential to understand the formation of secondary aerosols under high O₃ and low precursor gases to mitigate air pollution in the future. Full article

Ammonia (NH₃) is a naturally occurring, highly reactive and soluble alkaline trace gas, originating from both natural and anthropogenic sources. It is present throughout the biosphere, yet plays a complicated role in atmospheric acid–base reactions resulting in the formation of inorganic secondary inorganic aerosols (SIAs). While the general mechanisms are recognised, factors controlling the reactions leading to SIA formation are less explored. This review summarises the current knowledge of NH₃ sources, emission and deposition processes and atmospheric reactions leading to the formation of SIA. Brief summaries of NH₃ and SIA long-range transport and trans-boundary pollution, a discussion of precursor species to SIAs (other than NH₃), abiotic and biotic controls and state-of-the-art methods of measurement and modelling of pollutants are also included. In Ireland, NH₃ concentrations remained below National and European Union limits, until 2016 when a rise in emissions was seen due to agricultural expansion. However, due to a lack of continuous monitoring, source and receptor relationships are difficult to establish, including the appointment of precursor gases and aerosols to source regions and industries. Additionally, the lack of continuous monitoring leads to over- and underestimations of precursor gases present, resulting in inaccuracies of the estimated importance of NH₃ as a precursor gas for SIA. These gaps in data can hinder the accuracy and precision of forecasting models. Deposition measurements and the modelling of NH₃ present another challenge. Direct source measurements are required for the parameterization of bi-directional fluxes; however, high-quality data inputs can be limited by local micrometeorological conditions, or the types of instrumentation used. Long-term measurements remain challenging for both aerosols and precursor gases over larger areas or arduous terrains. Full article

Ammonia (NH₃) is one of the main precursors of secondary inorganic aerosols. In 2018, the NH₃ emissions of China’s cereal production (rice, wheat and maize) were estimated to be 3.3 Mt NH₃-N. Numerous NH₃ mitigation strategies have been developed in agriculture to reduce the emissions and improve air quality. However, due to the cost and unfeasibility of some developed techniques, the application of these mitigation measures is relatively slow in cropland. Therefore, developing low-cost, easy-operation, and feasible mitigation measures is an important breakthrough to solve the pollution of ammonia emissions in grain fields. The one-time deep application of nitrogen fertilizer in crop growing season, referred to as one-time application, is a promising ammonia mitigation measure for grain fields. It is a low-cost mode of fertilizer application suitable for grain fields as it saves labor and reduces the input of agricultural machinery. Therefore, incentive policies should be formulated to promote it for wide-range application in the whole country, especially in the areas with serious ammonia pollution, in order to achieve the goal of green and sustainable agricultural production. Full article

In order to explore the characteristics of water-soluble inorganic ions (WSIIs) in the atmosphere of Wanzhou, a small mountainous city in Chongqing, four representative seasonal PM_2.5 samples and gaseous precursors (SO₂ and NO₂) were collected from April 2016 to January 2017. The WSIIs (including Cl⁻, NO₃⁻, SO₄²⁻, Na⁺, NH₄ ⁺, K⁺, Mg²⁺, and Ca²⁺) were analyzed by ion chromatography. During the sampling period, daily PM_2.5 concentration varied from 3.47 to 156.30 μg·m⁻³, with an average value of 33.38 μg·m⁻³, which was lower than the second-level annual limit of NAAQS-China. WSIIs accounted for 55.6% of PM_2.5, and 83.1% of them were secondary inorganic ions (SNA, including SO₄²⁻, NO₃⁻, and NH₄⁺). The seasonal variations of PM_2.5 and WSIIs were similar, with the minimum in summer and the maximum in winter. PM_2.5 samples were the most alkaline in summer, weakly alkaline in spring and winter, and close to neutral in fall. The annual average ratio of NO₃⁻/SO₄²⁻ was 0.54, indicating predominant stationary sources for SNA in Wanzhou. NO₃⁻, SO₄²⁻, and NH₄⁺ mainly existed in the form of (NH₄)₂SO₄ and NH₄NO₃. The results of the principal component analysis (PCA) showed that the major sources of WSIIs in Wanzhou were the mixture of secondary inorganic aerosols, coal combustion, automobile exhaust (49.53%), dust (23.16%), and agriculture activities (9.68%). The results of the backward trajectory analysis showed that aerosol pollution in Wanzhou was mainly caused by local emissions. The enhanced formation of SNA through homogeneous and heterogeneous reactions contributed to the winter PM_2.5 pollution event in Wanzhou. Full article

Ammonia (NH₃) is an important precursor of secondary inorganic aerosols that affect air quality and human health. Livestock production is an essential source of NH₃ emissions, which exceeded half of the total NH₃ emissions in China. However, our understanding of the livestock point NH₃ emissions is still limited, due to the lack of both monitoring and statistical data. In this study, we established a satellite-based approach to estimating livestock point NH₃ emissions by combining satellite observations and digital maps of points-of-interest (POI). Taking a case study in Hebei province over China, 1267 livestock points were identified. The point livestock NH₃ emissions in 2020 ranged from 16.8 to 126.6 kg N ha⁻¹ yr⁻¹, with an average emission of 42.0 kg N ha⁻¹ yr⁻¹. The livestock NH₃ emissions in Hebei showed an overall increasing trend, with a growth rate of 5.8% yr⁻¹ between 2008 and 2020. In terms of seasonal changes, high livestock NH₃ emissions mainly occurred in spring and summer, while low NH₃ emissions were generally in autumn and winter. Satellite-derived point livestock NH₃ emissions in Hebei were 2–4 times that of bottom-up NH₃ emissions (EDGAR), suggesting that current used bottom-up emissions underestimated point livestock NH₃ emissions. This study proposed a framework for the satellite-based estimation of livestock NH₃ emissions, which is of great significance for relevant N management and NH₃ emission reduction policy formulation. Full article

To date, research regarding the changes of the sulfur and nitrogen rates in Wuhan during the summer is limited. In this study, we analyzed the air quality in Wuhan, China, using water-soluble ion, gaseous precursor, and weather data. A Spearman correlation analysis was then performed to investigate the temporal changes in air quality characteristics and their driving factors to provide a reference for air pollution control in Wuhan. The results indicate that SO₂ in the atmosphere at Wuhan undergoes secondary conversion and photo-oxidation, and the conversion degree of SO₂ is higher than that of NO₂. During the summers of 2016 and 2017, secondary inorganic atmospheric pollution was more severe than during other years. The fewest oxidation days occurred in summer 2020 (11 days), followed by the summers of 2017 and 2014 (25 and 27 days, respectively). During the study period, ion neutralization was the strongest in summer 2015 and the weakest in August 2020. The aerosols in Wuhan were mostly acidic and NH₄⁺ was an important neutralizing component. The neutralization factors of all cations showed little change in 2015. K⁺, Mg²⁺, and Ca²⁺ level changes were the highest in 2017 and 2020. At low temperature, high humidity, and low wind speed conditions, SO₂ and NO₂ were more easily converted into SO₄²⁻ and NO₃⁻. Full article

In order to explore the mechanism of haze formation, the meteorological effect and chemical reaction process of the explosive growth (EG) of PM_2.5 were studied. In this study, the level of PM_2.5, water-soluble inorganic ions, carbonaceous aerosols, gaseous precursors, and meteorological factors were analyzed in Shanghai in 2018. The EG event is defined by a net increase of PM_2.5 mass concentration greater than or equal to 100 μg m⁻³ within 3, 6, or 9 h. The results showed that the annual average PM_2.5 concentration in Shanghai in 2018 was 43.2 μg m⁻³, and secondary inorganic aerosols and organic matter (OM) accounted for 55.8% and 20.1% of PM_2.5, respectively. The increase and decrease in the contributions of sulfate, nitrate, ammonium (SNA), and elemental carbon (EC) to PM_2.5 from clean days to EG, respectively, indicated a strong, secondary transformation during EG. Three EG episodes (Ep) were studied in detail, and the PM_2.5 concentration in Ep3 was highest (135.7 μg m⁻³), followed by Ep2 (129.6 μg m⁻³), and Ep1 (82.3 μg m⁻³). The EG was driven by stagnant conditions and chemical reactions (heterogeneous and gas-phase oxidation reactions). This study improves our understanding of the mechanism of haze pollution and provides a scientific basis for air pollution control in Shanghai. Full article

This study explores the drivers of aerosol pH and their impact on the inorganic fraction and mass of aerosol in the S.E. Canadian urban environments of Hamilton and Toronto, Ontario. We find that inter-seasonal pH variability is mostly driven by temperature changes, which cause variations of up to one pH unit. Wintertime acidity is reduced, compared to summertime values. Because of this, the response of aerosol to precursors fundamentally changes between seasons, with a strong sensitivity of aerosol mass to levels of HNO₃ in the wintertime. Liquid water content (LWC) fundamentally influences the aerosol sensitivity to NH₃ and HNO₃ levels. In the summertime, organic aerosol is mostly responsible for the LWC at Toronto, and ammonium sulfate for Hamilton; in the winter, LWC was mostly associated with ammonium nitrate at both sites. The combination of pH and LWC in the two sites also affects N dry deposition flux; NO₃⁻ fluxes were comparable between the two sites, but NH₃ deposition flux at Toronto is almost twice what was seen in Hamilton; from November to March N deposition flux slows down leading to an accumulation of N as NO₃⁻ in the particle phase and an increase in PM_2.5 levels. Given the higher aerosol pH in Toronto, aerosol masses at this site are more sensitive to the emission of HNO₃ precursors compared to Hamilton. For both sites, NO_x emissions should be better regulated to improve air quality during winter; this is specifically important for the Toronto site as it is thermodynamically more sensitive to the emissions of HNO₃ precursors. Full article

Urban and suburban PM_2.5 samples were collected simultaneously during selected periods representing each season in 2019 in Zibo, China. Samples were analysed for water-soluble inorganic ions, carbon components, and elements. A chemical mass balance model and health risk assessment model were used to investigate the source contributions to PM_2.5 and the human health risks posed by various pollution sources via the inhalation pathway. Almost 50% of the PM_2.5 samples exceeded the secondary standard of China’s air quality concentration limit (75 µg/m³, 24 h). Water-soluble inorganic ions were the main component of PM_2.5 in Zibo, accounting for 50 ± 8% and 56 ± 11% of PM_2.5 at the urban and suburban sites, respectively. OC and OC/EC decreased significantly in the past few years due to enhanced energy restructuring. Pearson correlation analysis showed that traffic emissions were the main source of heavy metals. The Cr(VI) concentrations were 1.53 and 1.92 ng/m³ for urban and suburban sites, respectively, exceeding the national ambient air quality standards limit of 0.025 ng/m³. Secondary inorganic aerosols, traffic emissions, and secondary organic aerosols were the dominant contributors to PM_2.5 in Zibo, with the total contributions from these three sources accounting for approximately 80% of PM_2.5 and the remaining 20% attributed to traffic emissions. The non-carcinogenic risks from crustal dust for children were 2.23 and 1.15 in urban and suburban areas, respectively, exceeding the safe limit of 1.0 in both locations, as was the case for adults in urban areas. Meanwhile, the carcinogenic risks were all below the safe limit, with the non-carcinogenic and carcinogenic risks from traffic emissions being just below the limits. Strict control of precursor emissions, such as SO₂, NOx, and VOCs, is a good way to reduce PM_2.5 pollution resulting from secondary aerosols. Traffic control, limiting or preventing outdoor activities, and wearing masks during haze episodes may be also helpful in reducing PM_2.5 pollution and its non-carcinogenic and carcinogenic health impacts in Zibo. Full article

This study investigated the primary emissions and secondary aerosol formation from a gasoline direct injection (GDI) passenger car when operated over different legislative and real-world driving cycles on a chassis dynamometer. Diluted vehicle exhaust was photooxidized in a 30 m³ environmental chamber. Results showed elevated gaseous and particulate emissions for the cold-start cycles and higher secondary organic aerosol (SOA) formation, suggesting that cold-start condition will generate higher concentrations of SOA precursors. Total secondary aerosol mass exceeded primary PM emissions and was dominated by inorganic aerosol (ammonium and nitrate) for all driving cycles. Further chamber experiments in high temperature conditions verified that more ammonium nitrate nucleates to form new particles, forming a secondary peak in particle size distribution instead of condensing to black carbon particles. The results of this study revealed that the absorption of radiation by black carbon particles can lead to changes in secondary ammonium nitrate formation. Our work indicates the potential formation of new ammonium nitrate particles during low temperature conditions favored by the tailpipe ammonia and nitrogen oxide emissions from gasoline vehicles. Full article

High-resolution measurements of sulfur dioxide (SO₂), nitric acid (HNO₃), and hydrochloric acid (HCl) were conducted in Athens, Greece, from 2014 to 2016 via a wet rotating annular denuder system paired with an ion chromatograph. Decreased mean annual levels of SO₂ and HNO₃ (equal to 3.3 ± 4.8 μg m⁻³ and 0.7 ± 0.6 μg m⁻³, respectively) were observed relative to the past, whereas for HCl (mean of 0.4 μg m⁻³ ) no such comparison was possible as the past measurements are very scarce. Regional and local emission sources regulated the SO₂ levels and contributed to both the December and the July maxima of 6.6 μg m⁻³ and 5.5 μg m⁻³, respectively. Similarly, the significant enhancement at noon and during the winter nighttime was due to transported SO₂ and residential heating, respectively. The oxidation of NO₂ by OH radicals and the heterogeneous reactions of HNO₃ on sea salt seemed to drive the HNO₃ and HCl formation, respectively, whereas nighttime biomass burning affected only the former by almost 50%. During summer, the sulfate anions dominated over the SO₂, in contrast to the chloride and nitrate ions that prevailed during the winter and were linked to the aerosol acidity that influences their lifetime as well as their impact on ecosystems. Full article

The formation of inorganic fine particulate matter (i.e., iPM_2.5) is controlled by the thermodynamic equilibrium partitioning of NH₃-NH₄⁺. To develop effective control strategies of PM_2.5, we aim to understand the impacts of changes in different precursor gases on iPM_2.5 concentrations and partitioning of NH₃-NH₄⁺. To understand partitioning of NH₃-NH₄⁺ in the southeastern U.S., responses of iPM_2.5 to precursor gases in four seasons were investigated using field measurements of iPM_2.5, precursor gases, and meteorological conditions. The ISORROPIA II model was used to examine the effects of changes in total ammonia (gas + aerosol), total sulfuric acid (aerosol), and total nitric acid (gas + aerosol) on iPM_2.5 concentrations and partitioning of NH₃-NH₄⁺. The results indicate that reduction in total H₂SO₄ is more effective than reduction in total HNO₃ and total NH₃ to reduce iPM_2.5 especially under NH₃-rich condition. The reduction in total H₂SO₄ may change partitioning of NH₃-NH₄⁺ towards gas-phase and may also lead to an increase in NO₃⁻ under NH₃-rich conditions, which does not necessarily lead to full neutralization of acidic gases (pH < 7). Thus, future reduction in iPM_2.5 may necessitate the coordinated reduction in both H₂SO₄ and HNO₃ in the southeastern U.S. It is also found that the response of iPM_2.5 to the change in total H₂SO₄ is more sensitive in summer than winter due to the dominance of SO₄²⁻ salts in iPM_2.5 and the high temperature in summer. The NH₃ emissions from Animal Feeding Operations (AFOs) at an agricultural rural site (YRK) had great impacts on partitioning of NH₃-NH₄⁺. The Multiple Linear Regression (MLR) model revealed a strong positive correlation between cation-NH₄⁺ and anions-SO₄²⁻ and NO₃⁻. This research provides an insight into iPM_2.5 formation mechanism for the advancement of PM_2.5 control and regulation in the southeastern U.S. Full article