| Calculating ambient aerosol surface area concentrations using aerosol light scattering enhancement measurements Publication date: 1 November 2019 Source: Atmospheric Environment, Volume 216 Author(s): Ye Kuang, JiangChuan Tao, WanYun Xu, YingLi Yu, Gang Zhao, ChuanYang Shen, YuXuan Bian, ChunSheng Zhao Abstract
Aerosol surface area concentration () is crucial for studying atmospheric chemical reactions happened in aerosol water or on aerosol surface. However, there is no commercial instrument that can provide direct measurements of ambient . In this paper, we propose a method to calculate ambient based only on measurements of a three-wavelength humidified nephelometer system, which measures aerosol optical properties at three wavelengths under dry state and different relative humidity (RH) conditions. Two critical steps are required in this method: (1) Calculating surface area concentration of ambient aerosols in dry state, , using a trained random forest machine learning model based only on optical properties measured by the “dry” nephelometer. The proposed machine learning method is evaluated with particle number size distributions (PNSD) datasets from eight field campaigns conducted on the North China Plain during different seasons. The square of correlation coefficients between predicted and calculated for PNSD is about 0.99, the average ratio between predicted and calculated is 1.01 and 70% of data points has a relative difference less than 10%. (2) Calculating the surface area growth factor of ambient aerosol particles due to water uptake using the proposed parameterization scheme , and the hygroscopicity parameter can be calculated using measured aerosol light scattering enhancement factor and exponent. The ambient values during two field campaigns which are conducted on the North China Plain (Wangdu campaign and Gucheng campaign, in summer and winter respectively) are calculated using the proposed method. The ambient ranges from 42 to 1871 with an average of 319 during Wangdu campaign, and ranges from 19 to 4156 with an average of 788 during Gucheng campaign. Drastic daily variations of ambient are observed during these two campaigns. The results demonstrate that aerosol hygroscopic growth impacts significantly on variations in ambient especially under high RH conditions. The ranges from near 1 to 4 with an average of 1.4 during Wangdu campaign, and ranges from near 1 to 2.7 with an average of 1.3 during Gucheng campaign. The results indicate that the larger RH, the more sensitive becomes to variations in which highlights that real-time measurements of aerosol hygroscopicity are required for accurate calculations of ambient . The advantage of the proposed method is that the ambient can be obtained solely based on measurements of a three-wavelength humidified nephelometer system, facilitating real-time measurements of ambient and promoting studies in aerosol heterogeneous reactions.
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| Field testing a low-cost passive aerosol sampler for long-term measurement of ambient PM2.5 concentrations and particle composition Publication date: 1 November 2019 Source: Atmospheric Environment, Volume 216 Author(s): Maria D. Castillo, Jeff Wagner, Gary S. Casuccio, Roger R. West, Frank R. Freedman, Holger M. Eisl, Zhong-Min Wang, Jackson P. Yip, Patrick L. Kinney Abstract
While low-cost sensors can be valuable in assessing patterns of exposure to PM2.5 in cities, few sensors are optimal for monitoring long-term averages, the metric most relevant to long-term mortality risk, and none can readily determine particle composition. This study was designed to field-test a low-cost passive sampler (University of North Carolina Passive Aerosol Sampler, UNC-PAS) to measure long-term mass and elemental concentrations of PM2.5 in urban areas. We collected sequential 4-week and 12-week integrated samples over 1 year at eight sites in Boston, New York City and the San Francisco Bay Area with co-located federal reference and/or equivalent PM2.5 samplers. Field blanks and duplicates were included to assess sampling artifacts and precision, respectively. We analyzed filters for PM2.5 concentrations and elemental composition by site and by city using computer-controlled scanning electron microscopy coupled with energy dispersive spectroscopy, combined with theoretical sampling rates based on particle diameter. To improve UNC-PAS performance for submicron, carbonaceous particles typical of urban environments, we developed and evaluated refinements to standard particle analysis methods and deposition calculations. The analysis improvements yielded better performance for samples heavily impacted by wildfires, while the calculation improvements yielded better agreement with continuous and filter data across all sites. We observed good precision, with a single sample error coefficient of variation of 14.2%. Compared with co-located filter and continuous methods, the passive samplers were, on average, accurate to within 13.6% and −1.0%, respectively. Microscopic elemental and morphological analysis of individual particles showed contributions from vehicle combustion, salts, aged salt-carbon mixtures, biogenic spores, fly ash, and wildfire smoke. We conclude that the UNC-PAS can be a useful, complementary approach for long-term community monitoring, with the potential to improve spatial coverage and provide valuable information on composition and sources.
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| Key role of atmospheric water content in the formation of regional haze in southern China Publication date: 1 November 2019 Source: Atmospheric Environment, Volume 216 Author(s): Liuwei Kong, Min Hu, Qinwen Tan, Miao Feng, Yu Qu, Junling An, Yuanhang Zhang, Xingang Liu, Nianliang Cheng, Yijun Deng, Ruixiao Zhai, Zheng Wang Abstract
To elucidate the formation mechanism of haze and the important role of atmospheric humidity in haze formation, comprehensive observations were carried out at regional sites in the Pearl River Delta region of southern China from October 22 to November 6, 2014. Meteorological parameters, chemical compositions, aerosol secondary conversions and aerosol radiative forcing were analyzed. A lower wind speed (WS) and planetary boundary layer (PBL) can inhibit the horizontal and vertical diffusion of pollutants, leading to the accumulation of pollutant concentrations. A higher atmospheric relative humidity (RH) can promote aerosol secondary conversions, leading to an increase in secondary aerosol concentrations. Aerosol scattering hygroscopic growth properties and aerosol single scattering albedo (SSA) also increase with increasing RH, resulting in an increase in aerosol radiative forcing and a decrease in the PBL height, aggravating the formation of meteorological conditions that are not conducive to the dilution of pollutants. Conversely, a higher aerosol concentration also increases aerosol radiative forcing, forming a positive feedback loop. When the RH decreases and the WS increases, the loop enters a negative feedback process to reduce pollutant concentration.
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| Degradation mechanism of propylene carbonate initiated by hydroxyl radical and fate of its product radicals: A hybrid density functional study Publication date: 1 November 2019 Source: Atmospheric Environment, Volume 216 Author(s): Subrata Paul, Jones Deka, Ajanta Deka, Nand Kishor Gour Abstract
Degradation study of propylene carbonate (PC) with atmospheric oxidants are essential to understand its impact on the atmospheric environment and human health. Thus, we have analyzed the reaction mechanism and kinetics of PC with OH radical using quantum chemical study. In this regards, energies and frequencies calculations of all species involved in the possible oxidation channels (abstraction and addition) were performed using M06–2X functional along with 6–311++G (d,p) basis set. Our calculated energy results show that H-abstraction from –CH and –CH2 sites of PC are more dominant reaction channels compared to others. Further kinetic results also indicate that these two H-abstraction channels have a faster reaction rate. The calculated overall rate constant for the reaction was found to be 3.03 × 10−12 cm3 molecule−1 s−1 which is in good agreement with the experimental reported rate constant value (2.52 ± 0.51) × 10−12 cm3 molecule−1 s−1. The contributions of percent branching ratios of these two channels (H-abstraction from –CH and –CH2 sites of PC) were found to be 66% and 27% respectively, while other reaction channels have very small contributions to the overall rate. The atmospheric lifetime of PC for the reaction with OH radicals was found to be 3.8 days. Further, the degradation mechanisms of product radicals were also considered in this work. During this investigation, we found that [1,3]dioxolane-2,4-dione, 5-methy-[1,3]dioxolane-2,4-dione, acetyl formyl carbonate (CH3C(O)OC(O)OCHO, CH3CHO, CH2O and CO2 are the end products. These result also suggest that the formation of CH3C(O)OC(O)OCHO is thermodynamically more favourable end product.
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| Profile of foliar isoprenoid emissions from Mediterranean dominant shrub and tree species under experimental nitrogen deposition Publication date: 1 November 2019 Source: Atmospheric Environment, Volume 216 Author(s): Zhaobin Mu, Joan Llusià, Daijun Liu, Romà Ogaya, Dolores Asensio, Chao Zhang, Josep Peñuelas Abstract
Biogenic volatile organic compounds play important roles in atmospheric chemistry, and their emissions can be greatly influenced by the variations in environmental conditions and physiological activities caused by continuously increasing global nitrogen (N) deposition. However, this influence is still poorly understood, especially in a natural ecosystem. We conducted a one-year (2015–2016) experiment adding N deposition (60 kg N ha−1) with fertilization to a Mediterranean shrubland dominated by Erica multiflora and a Mediterranean forest dominated by Quercus ilex and compared the seasonal and daytime photosynthetic rates (A), stomatal conductances (gs) and rates of isoprenoid emission with control (2015–2016) and pre-treatment (2014–2015) plots. N fertilization increased A in warm weather as soil moisture increased, and assimilation became saturated when the environment was sufficiently favorable, and excess soil N significantly restrained A in cold weather. The plants were much more sensitive to soil water availability than N content and terpene emissions increased synergistically due to heat and drought stress in hot weather. N fertilization did not significantly affect isoprene emission but significantly increased total terpene emissions and decreased the diversity of terpenes. Our results suggest a successful acclimation of plants by emitting more isoprenoids under environmental stress and that N deposition will further stimulate emissions as the Mediterranean region becomes warmer and drier. The results highlight the necessity for predicting the most realistic future of ecosystems under global environmental change and for assessing the impacts of multiple factors acting in concert on plant physiological and ecosystem functioning including biogenic VOC emissions.
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| Impact of rainfall to the effectiveness of pig slurry shallow injection method for NH3 mitigation in a Mediterranean soil Publication date: 1 November 2019 Source: Atmospheric Environment, Volume 216 Author(s): Alberto Sanz-Cobena, Tom H. Misselbrook, Pedro Hernáiz, Antonio Vallejo Abstract
Ammonia emission from fertilized cropping systems is an important concern for stakeholders, particularly in regions with high livestock densities producing large amounts of manure. Application of pig slurries can result in very large losses of N through NH3 volatilization, thus decreasing the N use efficiency (NUE) of the applied manure. Shallow incorporation has been shown to significantly abate these losses. In this field study, we assessed the impact of contrasting weather conditions on the effectiveness of shallow injection to abate NH3 emissions from pig slurry application to a Mediterranean soil. As potential trade-offs of NH3 abatement, greenhouse gas emissions were also measured under conditions of high soil moisture. Compared with surface application of slurry, shallow injection effectively and significantly decreased NH3 losses independently of weather conditions, but reductions of NH3 emission were greater after heavy rainfall. In contrast, under these conditions, shallow injection triggered higher emissions of N2O and CH4. Our findings reinforce the idea that any single-pollutant abatement strategy needs to be designed and assessed in a regional context and considering potential trade-offs in the form of other pollutants.
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| Evaluating on-board sensing-based nitrogen oxides (NOX) emissions from a heavy-duty diesel truck in China Publication date: 1 November 2019 Source: Atmospheric Environment, Volume 216 Author(s): Ying Cheng, Liqiang He, Weinan He, Pei Zhao, Pinxi Wang, Jin Zhao, Kesong Zhang, Shaojun Zhang Abstract
Heavy-duty diesel vehicles (HDDVs) are important sources of urban nitrogen oxides (NOX). Understanding real-world NOX emissions from HDDVs is important because it has been shown that NOX emissions could far exceed the desired limits and impact human health. On-vehicle sensors for real-time emission evaluations have become commercially available, and China has adopted an on-board sensing (OBS) pilot program in Beijing. The OBS system utilizes information from the engine data networks which including real-time NOX concentrations from on-road HDDVs. To evaluate the accuracy of OBS monitoring, one of the vehicles in the OBS pilot program was equipped with a portable emissions measurement system (PEMS) and was evaluated over the course of two days during on-road comparison testing. The vehicle was operated under normal conditions and under conditions simulating a tampered vehicle with no urea for the selective catalytic reduction (SCR) system. A comparison between the OBS and PEMS exhibited good NOX correlations on an instantaneous and moving-average basis. Although large OBS-to-PEMS discrepancies were found in a small portion of instantaneous measurements, the 60-s moving averaged NOX concentrations exhibited good agreements across all the test conditions (Pearson's R > 0.95 and mean relative errors from −13% to +22%). During the tampered SCR simulation, the average vehicle emissions increased from 22 g kg fuel−1 to 48 g kg fuel−1, where both the PEMS and OBS quantified consistent trends. The actual NOX emissions, registered by the OBS over fifteen consecutive days of normal vehicle operation, ranged from 3.29 g km−1 to 6.65 g km−1. A comparison with the PEMS suggests the OBS can effectively and accurately identify high-emitting situations for in-use diesel vehicles. Recommendations are provided to improve the implementation of OBS programs in future applications.
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| Indoor and outdoor airborne bacterial air quality in day-care centers (DCCs) in greater Ahvaz, Iran Publication date: 1 November 2019 Source: Atmospheric Environment, Volume 216 Author(s): Atefeh Harbizadeh, Seyyed Abbas Mirzaee, Azar Dokht Khosravi, Farkhondeh Saleh Shoushtari, Hamed Goodarzi, Nadali Alavi, Kambiz Ahmadi Ankali, Hassan Dehdari Rad, Heidar Maleki, Gholamreza Goudarzi Abstract
Air pollution is considered as one of the major causes of environmental health problems. Young children and infants are more susceptible than adults due to age and higher sensitivity to environmental hazards. The aim of the present study was to an investigation of indoor/outdoor, regional and seasonal variations of airborne bacteria and PM concentrations of six randomly selected child day-care centers (DCCs) in greater Ahvaz. bio-aerosol sampling, PM measurement, and meteorological parameters data capture were performed monthly in DCCs of industrial, high traffic and residential regions during autumn, winter, and spring. The results revealed that the highest and the lowest of indoor and outdoor of mean concentrations of airborne bacteria were observed in the DCCs in the high traffic regions and residential area, respectively. The monthly highest and the lowest mean of culturable bacteria was determined in February (812 CFU/m3) and November (188 CFU/m3), respectively. There is a positive correlation between concentrations of PM and airborne bacteria in the DCCs during the study. The highest mean concentrations of airborne bacteria in indoor air samples were measured in winter season in high traffic and residential regions with 789 CFU/m3 and 646 CFU/m3, respectively, this value for outdoor samples was determined in spring and winter seasons at industrial and residential regions with 335.41 CFU/m3 and 306.34 CFU/m3, respectively. The highest and the lowest indoor/outdoor (I/O) ratio of mean concentrations of bacteria were determined in the autumn and spring at the industrial region with I/O ratio of 23.17 and 1.37, respectively. In the indoor and outdoor conditions of all DCCs, the Gram-positive bacteria were the dominant species which shows higher concentration than Gram-negative bacteria. The dominant bacterial genera were Bacillus spp. and Staphylococcus spp. in air samples. The results of the present study suggest strongly that instead of natural ventilation using windows, use of artificial ventilation and air conditioning systems could improve indoor air quality (IAQ) in the DCCs. Facial air filters and air treatment devices are recommended particularly at the time of dust event days in cities like Ahvaz.
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| Hydration of glycolic acid sulfate and lactic acid sulfate: Atmospheric implications Publication date: 1 November 2019 Source: Atmospheric Environment, Volume 216 Author(s): Narcisse T. Tsona, Lin Du Abstract
Organosulfates constitute an important component of secondary organic aerosols. Due to their polar and hydrophilic nature, organosulfates have the ability to bind with water and their water content may substantially affect the hygroscopicity of aerosols. However, there is poor information on how they interact with water and how their hydrates are distributed in the gas-phase. This study uses electronic structure calculations to investigate the structures and thermodynamics of water uptake by glycolic acid sulfate and lactic acid sulfate in the gas-phase, and the equilibrium distributions of their hydrates at varying degrees of humidity and different temperatures. Given the demonstrated diverse role of neutral and charged species in aerosol formation, the hydration of these organosulfates, both electrically neutral and negatively charged (deprotonated) were investigated. We find that electrically neutral glycolic acid sulfate is more extensively hydrated than its deprotonated counterpart, forming relatively high concentrations of mono-, di-, and tri-hydrates at most tropospheric temperatures and relative humidity, while the latter mostly forms the monohydrate at similar conditions. The opposite situation is observed for lactic acid sulfate where the deprotonated form is the most extensively hydrated, despite their hydrates are formed at low concentrations. However, due to high dissociation constants of organosulfates coupled to their increasing partition to the particle phase with increasing relative humidity, the hydrates of electrically neutral organosulfates studied here would mostly partition into the particle phase and reinforce the effects of their corresponding deprotonated counterparts in altering the hygroscopic properties of aerosol particles. This study can serve as a basis to evaluate the hydration pattern of other organosulfates and assess their implications in aerosol formation.
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| Traffic source impacts on chlorinated polycyclic aromatic hydrocarbons in PM2.5 by short-range transport Publication date: 1 November 2019 Source: Atmospheric Environment, Volume 216 Author(s): Ryosuke Oishi, Yuki Imai, Fumikazu Ikemori, Takeshi Ohura Abstract
Chlorinated polycyclic aromatic hydrocarbons (ClPAHs) are recognized as ubiquitous hazardous pollutants in the environment, whereas their behavior in local areas remains unclear. Additionally, there is limited information on the sources in local areas. Here, we investigated the seasonal trends of ClPAHs associated with fine particles (PM2.5) at two sites near heavy traffic roads to evaluate the local atmospheric behaviors and sources. The annual mean concentrations of total ClPAHs at the north (site A) and south side (site B) across a heavy traffic road were 12.0 and 19.2 pg/m3, respectively. The higher concentration at site B was further emphasized during the winter season; at that time the site was located beneath the wind from the traffic road. In addition, for individual ClPAHs, the behaviors of 8-chlorofluoranthene (8-ClFluor) and 7-chlorobenz[a]anthracene (7-ClBaA) were consistent with the frequency of the north wind, suggesting that 8-ClFluor and 7-ClBaA have the ability to be indicators of vehicle exhaust. Diagnostic ratios using these specific ClPAHs during high-traffic activities provided the specific values to differentiate the impacts.
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Κυριακή 8 Σεπτεμβρίου 2019
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