Dry Deposition Fluxes Research Articles

Deposition characteristics, source identification and potential risk assessment on soil of atmospheric potentially toxic elements dry deposition in Shenyang, China

Compared with atmospheric bulk/wet deposition, dry deposition has lacked evaluation for a long time. A new method was used to determine and evaluate the atmospheric potentially toxic elements (PTEs) dry deposition at the urban site (US) and the rural site (RS) from early 2019 to February 2022 in Shenyang, China. The dry deposition fluxes of most PTEs were greater at the US than the RS (p < 0.01), with the exception of those of Cd and Pb. We also found that atmospheric Cr dry deposition was more severe in Shenyang with respect to the global scale, especially in the urban area (36.29 mg/(m2·yr)). Based on the principal component analysis and correlation analysis, Cd and Pb in the urban area originated from transportation, whereas Ni, Cu, Cr and Zn originated from natural processes and other anthropogenic activities that could produce airborne dust. Additionally, Cd and Pb at the RS came from road traffic, Cr, Cu and Zn originated from other human activities, and Ni was mostly of natural origin. According to the predictions based on the potential risk assessment model, the contamination risk for PTEs in the surface soils of development land under the influence of atmospheric deposition would be low in the long term, but the risk for Cd in agricultural land warrants more attention because it was predicted to exceed the risk screening value within 3 years. Furthermore, atmospheric deposition and the application of pig manure could lead to a rapid increase in the Cd concentration in experimental fields.

Dry deposition fluxes, source, and potential ecological impact of amino acids in the Danjiangkou Reservoir of China's South-to-North water transfer project

As a nitrogen source for biological growth, amino compounds can participate in global nitrogen cycle processes and directly impact ecosystems. Dry deposition samples were collected from September 2020 to August 2021 from the Danjiangkou Reservoir of the South-to-North Water Transfer Project. The dry deposition characteristics of amino acids in the reservoir area were analyzed, their sources were resolved, and the potential ecological impacts were evaluated. The results showed that the dry deposition flux of dissolved free amino acids was 0.48 kg N ha−1 yr−1 and that of dissolved combined amino acids was 1.09 kg N ha−1 yr−1 in Danjiangkou Reservoir. The dominant amino acid fractions were glutamic acid and aspartic acid. Agricultural activities, coal combustion, and primary biogenic particles influenced the amino acid deposition in the reservoir area. The potential source areas for amino acid deposition mainly influenced the northeast, southwest, northwest, and south of the reservoir. The amounts of amino acids entering the water bodies via dry deposition was 85.72 t N yr−1, contributing 0.83 g C m−2 yr−1 of new production to the reservoir water bodies. To summarize, this research depicted that the potential ecological impact of dry deposition of amino acids on artificial freshwater lakes should not be overlooked.

Amino acids in the water-soluble and water-insoluble fractions of the aerosols at a forested site in Japan

In order to clarify the concentration levels and sources of the water-insoluble amino acids (WIAA) in aerosols that have been received little attention in previous studies and to discuss their potential impact on nitrogen deposition, the WIAA in the coarse-mode (d = 2.0–10 μm) and fine-mode (d < 2.0 μm) aerosols were measured at a forested site in Japan together with the water-soluble free and combined amino acids. The sum of the WIAA showed more than a 6-times higher concentration than that of the water-soluble amino acids in the coarse-mode range and a similar concentration to that in the fine-mode range, which suggests a significant contribution of the WIAA to the amino acids pool in aerosols. The WIAA were predominantly partitioned into the coarse-mode range. The concentration of the coarse-mode WIAA was the highest in the summer and a strong correlation was found between the coarse-mode WIAA and nss-K+ concentrations. These results suggest that plant debris and the associated materials are important sources for the coarse-mode WIAA and the increase in the suspension of these particulate materials caused the enhancement of the WIAA in the summer. Remarkably higher concentrations of the coarse-mode WIAA than the water-soluble amino acids would be caused by these particulate materials. In the fine-mode range, on the other hand, the concentration of the WIAA was the highest in the spring and strongly correlated with the fine-mode nss-K+ concentrations. The fine-mode WIAA would be mainly derived from the biomass burning particles. The coarse-mode WIAA were estimated to significantly contribute to the dry deposition flux of the total nitrogen. The present study implies a potential impact of the WIAA in the coarse aerosols on nitrogen deposition.

Multi-time Scale Variation of Atmospheric Ammonia Concentration and Dry Deposition in a Paddy Rice Region in Subtropical China

Meteorological factors and anthropogenic activities significantly affect atmospheric ammonia （NH3） concentration and its dry deposition. Former studies have examined the spatial and temporal variability in atmospheric NH3 concentrations at monthly scales. However, the characteristics of atmospheric concentrations at finer time scales such as hourly and daily scales and the influencing factors remain unclear. In this study, atmospheric NH3 concentration and related meteorological factors were continuously monitored online for one year in a double cropping rice region in subtropical China, and atmospheric NH3 concentration and its meteorological influencing factors as well as dry deposition were analyzed at different time scales （hourly, daily, and monthly）. The main results were as follows： The annual average daily concentration of NH3 in the rice area varied from 0.01 to 58.0 μg·m-3 （in N, same below）, and the annual average concentration was 5.3 μg·m-3. On the hourly scale, the 24-hour dynamics of atmospheric NH3 concentration showed a unimodal pattern, and the time of the NH3 peak appearance in different seasons was different； the time of the peak that appeared in winter lagged behind that in the other seasons. From the perspective of daily scale, NH3 concentration was mainly affected by fertilization in the paddy fields, peaking at 1-3 days after fertilization and then gradually decreasing. On the monthly scale, NH3 concentration peaked at 12.8 μg·m-3 in July and was the lowest in October at 1.6 μg·m-3. On the hourly scale, NH3 concentration varied seasonally due to the influences of meteorological factors, mainly as follows： NH3 concentration showed significant positive correlations with air temperature and solar radiation in all four seasons and with wind speed in spring and summer, whereas it showed significant negative correlations with relative humidity except in winter. On the daily scale, NH3 concentration showed a significant positive correlation with air temperature, rainfall, and solar radiation, whereas it showed a significant negative correlation with relative humidity. On the monthly scale, no significant correlation existed between each meteorological factor and NH3 concentration. The annual dry deposition flux （in N） calculated from the hourly average NH3 concentration was 8.5 kg·（hm2·a）-1, which was 11.6% higher than the annual flux calculated from the daily average and 12.4% higher than the annual flux calculated from the monthly average. In summary, there were significant daily and seasonal variations in atmospheric NH3 concentration in the paddy rice region in subtropical China, and conducting hourly-scale observations of NH3 concentration can help to reveal the multi-time scale variations in NH3 concentration and to quantify NH3 dry deposition more accurately.

Understanding the role of atmospheric deposition on the environmental load of per- and polyfluoroalkyl substances: A case study in Three Gorges Reservoir, China

Sixty-nine total suspended particle (TSP) samples, paired with forty-eight surface soil samples, covering four seasons from January 2021 to November 2021, were collected from the Three Gorges Reservoir Region (TGRR). Twenty per- and poly-fluoroalkyl substances (PFASs) were analyzed to evaluate their contamination characteristics and understand the role of atmospheric deposition on the environmental loads in TGRR. The annual average concentrations of PFASs in TSP and soil were 37.2 ± 1.22 pg·m−3 and 0.798 ± 0.134 ng·g−1, respectively. For TSP, concentrations were highest in spring and lowest in summer. For soil, it was in autumn and winter, respectively. The seasonality was more influenced by anthropogenic activities than by meteorological conditions or physicochemical parameters of the soil. Positive matrix fractionation (PMF) indicated that, based on annual averages, PFOA-based products (40.2 %) were the major sources of PFASs in TSP, followed by PFOS-based products (25.2 %) and precursor degradation (34.6 %). The highest source contributor for PFASs in spring was precursor degradation (40.9 %), while in other three seasons, it was PFOA-based products (39.9 %, 40.9 % and 52.0 %, respectively). The mean atmospheric dry and wet deposition fluxes of PFASs were estimated at 4.38 ng·m−2·day−1 and 23.5 ng·m−2·day−1, respectively. The contribution of atmospheric deposition to the inventory mass of PFASs in the surface soil was 22.3 %. These findings fill a gap in knowledge regarding the processes and mechanisms of the occurrence, sources and atmospheric deposition of PFASs in the TGRR.

Urban air PCDD/Fs: Dry deposition fluxes and mass transfer coefficients determined using a water surface sampler

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) cause significant environmental concerns. Atmospheric PCDD/Fs permeate water bodies and other ecosystems through wet and dry deposition. In an urban site, dry deposition flux samples of gaseous phase PCDD/Fs were collected by a water surface sampler (WSS) operated between June 2022 and June 2023. There is a conspicuous absence of literature on the direct measurement of dry deposition flux levels in the gaseous phase of PCDD/Fs. In the study, PCDD/Fs in the gas phase reaching the WSS dissolved in the water according to Henry's Law. The PCDD/Fs in the water were transferred to an XAD-2 resin column, sorbing the dissolved PCDD/Fs. The average monthly gas phase dry deposition flux was 34.07 ± 9.35 pg/m2-day (7.35 ± 2.16 pg I-TEQ/m2-day). The highest flux was measured in March (49.53 pg/m2-day), and the lowest was in August (18.64 pg/m2-day). These values indicated the direct flux from air to water. The atmospheric concentration of the gas-phase ranged from 68.38 to 126.88 fg/m3 (13.22–25.01 fg I-TEQ/m3). Dry deposition fluxes and concentrations of atmospheric PCDD/Fs were bigger in the colder months than in the warmer months. This was probably due to a significant increase in residential heating during the colder months, decreased photochemical reactions, and lower mixing heights. Regarding congeners in the dry deposition flux and concentration values in I-TEQ units, 2,3,7,8-TCDD compound predominated with the proportions of 31.61 ± 7.76% and 29.09 ± 12.34%, respectively. Concurrently measured dry deposition flux (Fg) and ambient air concentration (Cg) of PCDD/Fs were considered in the determination of mass transfer coefficient (MTC = Fg/Cg) calculation for each PCDD/F congener. The average MTC for targeted 17 PCDD/Fs was 0.45 ± 0.15 cm/s, and it fluctuated between 0.89 ± 0.30 cm/s for 2,3,7,8-TCDF and 0.2 ± 0.16 cm/s for OCDD.

Depositions of airborne microplastics during the wet and dry seasons in Pathum Thani, Thailand

In this study, microplastics were monitored separately in the wet and dry deposition in the peri-urban area of Thailand. Over eighteen weeks from September 2021 to January 2022, rainwater (wet deposition) and settled microplastics (dry deposition) were systematically collected. Subsequent analyses involved the extraction, quantification, and identification of microplastics through wet peroxide oxidation, density separation, stereomicroscopic visual inspection and Fourier-transform infrared (FTIR) analysis. The results show that the wet deposition flux of microplastics was averaged at 285 numbers/m2/day while the dry deposition flux of microplastics was averaged at 199 numbers/m2/day, contributing to a total deposition flux (dry + wet) of 325 numbers/m2/day. Comparative assessments with prior studies from different locations demonstrated similarities in microplastic numbers, color and polymer types. Notably, this study found a higher microplastic deposition flux during the period when wet deposition existed than the flux during the period with only dry deposition, underscoring the important role of rainfall in adding more removal of microplastics from the atmosphere. These findings provide crucial insights into the dynamics of microplastic deposition in outdoor settings, significantly contributing to understanding the microplastic pollution cycle in the environment.

Aerosol soluble proteins in Asian dust in southwestern Japan

Aerosol proteins, as core biological components of bioaerosols, are garnering increasing attention due to their environmental significance, including their roles in atmospheric processes and associated health risks. However, observational data on the proteins are very limited, leaving their distribution and variation in the atmosphere poorly understood. To investigate the long-distance transport of proteins with Asian dust in the Northern Hemisphere middle latitude westerlies to remote downwind areas, we quantified the soluble proteins in aerosol particles, referred to as aerosol soluble proteins (ASPs), collected in the coastal city of Kumamoto, Japan, during the spring of 2023, when three dust events occurred. The concentration of ASPs ranged from 0.22 to 1.68 μg m−3, with an average concentration of 0.73 ± 0.36 μg m−3 under dust conditions and 0.31 ± 0.05 μg m−3 under non-dust conditions. During the dust periods, the largest concentration of ASPs (1.68 μg m−3) coincided with the peak concentration of suspended particulate matter, and the concentration strongly correlated with the mass concentration of particles larger than 2.5 μm, indicating a close dependence of ASPs on dust particles. Primary estimations indicated a dry deposition flux of ASPs at approximately 1.10 ± 0.87 mg m−2 d−1 under the dust conditions. These results prove that Asian dust efficiently transports proteins, facilitating their dispersion in the atmosphere.

Impact of gas dry deposition parameterization on secondary particle formation in an urban canyon

This study investigates the impact of the parameterization of dry deposition on the local gas-particle partitioning between ammonium nitrate NH4NO3 and its precursor gases (ammonia, NH3 and nitric acid, HNO3) through chemistry-coupled large-eddy simulations on the dispersion of reactive gaseous and particulate pollutant in an idealized street canyon. A key factor in the parameterization of dry deposition is the effective Henry's Law constant H*. Three distinct characterizations of H* are compared: two drawn from existing literature (referred to as Model 1 and Model 2) and one typical of low pH conditions (referred to as Model 3), which could be more representative of urban areas. Model 3 shows contrasting gas-particle partitioning results between NH3, HNO3, and NH4NO3 with Model 1 and Model 2. In detail, the NH4NO3 concentrations in the street of Model 1 and Model 2 are smaller than the background NH4NO3 concentration. However, Model 3 shows higher NH4NO3 concentration in the street than the background NH4NO3 concentration. This is because the dry deposition fluxes of NH3 and HNO3 are higher in Model 1 and Model 2 than in Model 3, resulting in less available NH3 and HNO3 for NH4NO3 formation. These findings highlight the importance of selecting an appropriate H* characterization that is tailored to the specific environmental conditions under investigation.

Contribution of emissions from the oil sands activities in Alberta, Canada to atmospheric concentration and deposition of nitrogen and sulfur species at a downwind site

Oil sands activities in the Athabasca Oil Sands Region in Alberta, Canada, are large sources of atmospheric NOx and SO2. This study investigated the impact of oil sands emissions on the atmospheric deposition of nitrogen and sulfur species at a downwind site, about 350 km from the oil sands facilities. Measurement data are from the Canadian Air and Precipitation Monitoring Network (CAPMoN) from 2015 to 2019, including ambient concentrations of HNO3, pNO3-, NO2, pNH4+, NH3, SO2, pSO42− and base cations, as well as concentrations of NO3−, SO42−, NH4+, and base cations in precipitation. Sector analysis of air mass back trajectories was conducted to distinguish measurements with different air mass origins. Median atmospheric concentrations and dry deposition fluxes of HNO3, pNO3-, NO2, pNH4+, pSO42−, and SO2 on days when the air masses came from the oil sands sector were significantly greater than those with the “Clean” sector by 34–67%, whereas the difference in NH3 concentration was not significant. Contributions of the oil sands emissions to dry deposition fluxes of these species ranged from 3.8 to 13.1%. The precipitation-weighted mean concentrations of NO3−, SO42−, and NH4+ in samples with the oil sands sector were 76 %, 65 % and 81 % greater than those with the “Clean” sector, respectively. Contributions of the oil sands emissions to wet deposition of NO3−, SO42−, and NH4+ were 12.5 ± 8.9 %, 8.7 ± 4.4 %, and 6.0 ± 3.3 %, respectively. The annual total deposition of nitrogen and sulfur were 1.9 kg-N ha−1 and 0.74 kg-S ha−1, respectively, of which 8.0 ± 3.5 % and 8.7 ± 3.6 % were from oil sands emissions. The total deposition of sulfur and nitrogen did not exceed the critical loads (CL) of acidity, but nitrogen deposition exceeded the CLs of nutrient nitrogen in the region.

Atmospheric wet and dry phosphorus deposition in Lake Erhai, China

Lake Erhai is a potentially phosphorus (P)-limited lake and its water quality may have been affected by atmospheric P deposition. However, there have been few studies on atmospheric P deposition in this lake. In this study, we established five wet deposition monitoring sites and two dry deposition monitoring sites around Lake Erhai to quantify the wet and dry deposition of total phosphorus (TP), including dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP) and particulate phosphorus (PP) from July 2022 to June 2023. Wet deposition fluxes of P species were collected by automatic rainfall collection instrument, and dry deposition fluxes were estimated using airborne concentration measurements and inferential models. The results reveal that among the different P components, DOP had the highest contribution (50%) to wet TP deposition (average all sites 12.7 ± 0.7 mg P m2/yr), followed by PP (40%) and DIP (10%). Similarly, DOP (51%) was the major contributor to dry TP deposition (average two sites 2.4 ± 0.9 mg P m2/yr), followed by DIP (35%) and PP (14%). Wet deposition dominated the annual total TP deposition (wet plus dry), accounting for approximately 83%. The key seasons for dry deposition were spring and autumn, which accounted for 64% of the annual total dry TP deposition. In comparison, wet deposition was significantly higher in the summer, accounting for 73% of the annual total wet TP deposition. The results of the potential source contribution function and concentration-weighted trajectories analysis indicate that local source emission and long-range transport from surrounding cities jointly exerted a substantial influence on aerosol P concentrations, particularly in the eastern and northwestern regions of the lake. These findings provide a comprehensive understanding of the different P components in atmospheric deposition, which is beneficial for developing effective strategies to manage the P cycle in Lake Erhai.

Dry deposition fluxes and inhalation risks of toxic elements in total suspended particles in the Bohai Rim region: Long-term trends and potential sources

Long-term changes in dry deposition fluxes (DDF) and health risks for toxic elements (TE) in total suspended particles (TSP) in the Bohai Rim region are important for assessing control effects of pollution sources. Thus, we investigated the trends in DDF and concentrations for TSP and TE and health risks of TE in eight cities in the region from 2011–2020. TSP concentration and DDF showed general downward trends. Compared to the before Clear Air Action Plan (BCAAP, 2011–2012) period, concentration and DDF of TE over the Clear Air Action Plan (CAAP, 2013–2017) period substantially decreased, with the highest decrease rates in Zn, Cd, and Cr. During the study period, non-carcinogenic (HI) and total carcinogenic (TCR) risks for children and adults were 0.09 and 0.04, and 1.54 × 10−5 and 2.65 × 10−5, respectively, with Cr6+ and As being dominant contributors. Compared to the BCAAP period, HI and TCR over the CAAP period decreased by 36.8 % and 32.4 %, respectively. However, their risks increased over the Blue Sky Protection Campaign (BSPC, 2018–2020) period. Potential source contribution function suggested substantial changes in potential risk areas over different control periods, with the BSPC primarily being on land and the Yellow Sea.

Analysis of the global atmospheric background sulfur budget in a multi-model framework

Abstract. A growing number of general circulation models are adapting interactive sulfur and aerosol schemes to improve the representation of relevant physical and chemical processes and associated feedbacks. They are motivated by investigations of climate response to major volcanic eruptions and potential solar geoengineering scenarios. However, uncertainties in these schemes are not well constrained. Stratospheric sulfate is modulated by emissions of sulfur-containing species of anthropogenic and natural origin, including volcanic activity. While the effects of volcanic eruptions have been studied in the framework of global model intercomparisons, the background conditions of the sulfur cycle have not been addressed in such a way. Here, we fill this gap by analyzing the distribution of the main sulfur species in nine global atmospheric aerosol models for a volcanically quiescent period. We use observational data to evaluate model results. Overall, models agree that the three dominant sulfur species in terms of burdens (sulfate aerosol, OCS, and SO2) make up about 98 % stratospheric sulfur and 95 % tropospheric sulfur. However, models vary considerably in the partitioning between these species. Models agree that anthropogenic emission of SO2 strongly affects the sulfate aerosol burden in the northern hemispheric troposphere, while its importance is very uncertain in other regions, where emissions are much lower. Sulfate aerosol is the main deposited species in all models, but the values deviate by a factor of 2. Additionally, the partitioning between wet and dry deposition fluxes is highly model dependent. Inter-model variability in the sulfur species is low in the tropics and increases towards the poles. Differences are largest in the dynamically active northern hemispheric extratropical region and could be attributed to the representation of the stratospheric circulation. The differences in the atmospheric sulfur budget among the models arise from the representation of both chemical and dynamical processes, whose interplay complicates the bias attribution. Several problematic points identified for individual models are related to the specifics of the chemistry schemes, model resolution, and representation of cross-tropopause transport in the extratropics. Further model intercomparison research is needed with a focus on the clarification of the reasons for biases, given the importance of this topic for the stratospheric aerosol injection studies.

Atmospheric deposition studies of microplastics in Central Germany

Emission of microplastics (MP) to the atmosphere, airborne transport, and subsequent deposition are now recognized. However, the temporal and spatial resolution of data on MP pollution and knowledge of their atmospheric behaviour and fate is still very limited. Hence, we investigated MP wet and dry deposition in Central Germany and examined the role of weather conditions on MP contamination levels. Monthly samples of dry and wet deposition were taken over an eight-month period (05/2019-12/2019) and analysed by micro-Fourier-Transform Infrared spectroscopy (µFTIR) down to 11 μm particle size and one dry deposition sample was subjected to Raman analysis to determine plastic particles down to a size of 0.5 μm. MP in a size range from 11 μm to 130 μm were detected in all wet deposition samples and in 4 out of 8 dry deposition samples by µFTIR. Polypropylene particles were found most frequently and accounted for 62% and 54% of all particles in wet and dry deposition samples, respectively. Over the eight-month period, wet deposition of MP slightly dominated at the study site and comprised 59% of the total MP deposition. The MP mean total (wet + dry) deposition flux (DF) was 17 ± 14 MP m− 2 day− 1. Extensive Raman analyses of an exemplary dry deposition sample revealed additional plastic particles in the extended size range from 1 to 10 μm resulting in a deposition flux of 207 MP m− 2 day− 1. Our results suggest that MP analysis by µFTIR down to 11 μm may underestimate DF at least by an order of magnitude. More comprehensive studies on submicron plastics and nanoplastics are needed to fully assess air pollution by plastic particles.

Observation of ozone deposition flux and its contribution to stomatal uptake over a winter wheat field in eastern China

Ground-level ozone (O3) poses a significant threat to food security in China. Therefore, it is imperative to conduct a comprehensive scientific evaluation of the potential hazards posed by O3 to agricultural crops. This study continuously observed variation in meteorological factors, O3 concentration, O3 deposition rate and flux, and quantified the distribution characteristics of O3 deposition flux in stomatal and non-stomatal pathways. Results suggested that the O3 dry deposition rate and flux in winter wheat fields exhibited relatively stable variations at night but pronounced fluctuations during the day. Their mean values were 0.31 cm s−1 and -0.0044 μmol m−2·s−1, respectively, with peak values occurring at 08:30 and 14:00. The cumulative O3 total flux during the main growth season of winter wheat was 26.1 mmol m−2, with stomatal and non-stomatal fluxes accounting for 7.7 mmol m−2 and 18.4 mmol m−2, respectively. The proportions of total O3 flux in stomatal and non-stomatal channels were 29.5% and 70.5%, respectively, with daytime proportions being 39.7% and 60.3%, respectively. These findings provide crucial insights for future accurate assessments of crop yield loss due to O3 at the earth's surface.

Emissions and Atmospheric Dry and Wet Deposition of Trace Metals from Natural and Anthropogenic Sources in Mainland China

Trace metals from natural and anthropogenic sources impact the atmospheric environment and enter the soil through dry and wet atmospheric deposition, ultimately affecting human health. In this study, we established an emission inventory of Pb, As, Cr, and Cd in East Asia (80° E–140° E, 15° N–50° N) for the year 2017, including dust and anthropogenic sources from both land and marine. We modified the Community Multiscale Air Quality (CMAQ) model to provide gridded data on concentrations, as well as dry and wet atmospheric deposition fluxes of metals, with a focus on mainland China. The emissions of Pb, As, Cr, and Cd in East Asia were 19,253, 3415, 3332, and 9379 tons, respectively, in 2017, with 55%, 69%, 25%, and 58% distributed in the fine mode. The spatial distribution of atmospheric concentrations and dry deposition of trace metals was similar to that of emissions, while the spatial distribution of precipitation-related wet deposition was further east and greater in the south than in the north. In mainland China, the average bulk-deposition fluxes of Pb, As, Cr, and Cd were 1036.5, 170.3, 465.9, and 185.0 μg·m−2·year−1, respectively. Our study provides gridded data on trace metals in mainland China, which can be used for assessing air quality, human exposure risks, and metal inputs to soils.

Leaf-Level Bidirectional Exchange of Formaldehyde on Deciduous and Evergreen Tree Saplings.

Gas-phase formaldehyde (HCHO) is formed in high yield from the oxidation of many volatile organic compounds (VOCs) and is commonly used as a constraint when testing the performance of VOC oxidation mechanisms in models. However, prior to using HCHO as a model constraint for VOC oxidation in forested regions, it is essential to have a thorough understanding of its foliar exchange. Therefore, a controlled laboratory setup was designed to measure the emission and dry deposition of HCHO at the leaf-level to red oak (Quercus rubra) and Leyland cypress (Cupressus × leylandii) tree saplings. The results show that HCHO has a compensation point (CP) that rises exponentially with temperature (22-35 °C) with a mean range of 0.3-0.9 ppbv. The HCHO CP results are also found to be independent of the studied tree species and 40-70% relative humidity. Given that HCHO mixing ratios in forests during the daytime are usually greater than 1 ppbv, the magnitude of the CP suggests that trees generally act as a net sink of HCHO. Additionally, the results show that HCHO foliar exchange is stomatally controlled and better matches a reactivity factor (f0) of 0 as opposed to 1 in conventional dry deposition parametrizations. At 30 °C, daytime HCHO dry deposition fluxes are reduced by upward of 50% when using f0 = 0 and a nonzero HCHO CP, although deposition remains the dominant canopy sink of HCHO. A reduced deposition sink also implies the increased importance of the gas-phase photolysis of HCHO as a source of HO2.

Characteristics of Cd Fluxe in Topsoil Around Typical Mining Area in Hezhou, Guangxi

Guangxi is a typical geological high background area in southwest China, where carbonates, black rock series, basic-ultrabasic rock mass, and metal deposits (mineralized bodies) exhibit strong weathering into loam, resulting in higher cadmium (Cd) content in the soil than that in other areas of China. In order to investigate the degree of influence of mining activities on topsoil environmental quality in the area with high geological background, we chose a mining area and control area in Hezhou for this research and systematically carried out a comparative study on Cd transport routes and transport flux density in topsoil. The results showed that the average atmospheric dry and wet deposition flux densities of Cd in the soil of the mining area and control area were 1.87 g·(hm2·a)-1 and 1.52 g·(hm2·a)-1, accounting for 61.5% and 60.3% of the total input flux density, respectively. The flux density of Cd in the soil by fertilization and irrigation was lower. Surface water infiltration was the main avenue of soil Cd output in both the mining area and control area, accounting for 75.4% and 86.6% of the total output flux density, respectively. The harvest output flux density in the mining area was higher than that in the control area, and the Cd content of rice planted in the mining area was higher than the standard, whereas that of maize was safe. On the whole, the net transport flux densities of soil Cd in the mining area and control area were -3.05 g·(hm2·a)-1 and -4.05 g·(hm2·a)-1, both of which showed Cd leaching in the soil. However, the points of high atmospheric deposition flux density and exceeding Cd content in rice were mainly distributed around the mining area, which may have posed a potential threat to the health of local residents. Therefore, it is suggested to control the soil Cd pollution through monitoring and planting structure adjustment.

Improving Simulation of Gas‐Particle Partitioning of Atmospheric Mercury Using CMAQ‐newHg‐Br v2

AbstractMercury (Hg) is a global pollutant whose atmospheric deposition is a major input to the terrestrial and oceanic ecosystems. Gas‐particle partitioning (GPP) of gaseous oxidized mercury (GOM) redistributes speciated Hg between gas and particulate phase and can subsequently alter Hg deposition flux. Most 3‐dimensional chemical transport models either neglected the Hg GPP process or parameterized it with measurement data limited in time and space. In this study, CMAQ‐newHg‐Br (Ye et al., 2018, https://doi.org/10.1002/2017ms001161) was updated to CMAQ‐newHg‐Br v2 by implementing a new GPP scheme and the most up‐to‐date Hg redox chemistry and was run for the northeastern United States over January‐November 2010. CMAQ‐newHg‐Br v2 reproduced the measured spatiotemporal distributions of gaseous elemental mercury (GEM) and particulate bound mercury (PBM) concentrations and Hg wet deposition flux within reasonable ranges and simulated dry deposition flux in agreement with previous studies. The GPP scheme improved the simulation of PBM via increasing winter‐, spring‐ and fall‐time PBM concentrations by threefold. It also improved simulated Hg wet deposition flux with an increase of 2.1 ± 0.7 μgm2 in the 11‐month accumulated amount, offsetting half of the decreasing effect of the updated chemistry (−4.2 ± 1.8 μgm2). Further, the GPP scheme captured the observed Kp‐T relationship as reported in previous studies without using measurement data and showed advantages at night and in rural/remote areas where existing empirical parameterizations failed. Our study demonstrated CMAQ‐newHg‐Br v2 a promising assessment tool to quantify impacts of climate change and emission reduction policy on Hg cycling.

Significant Increase in Ammonia Emissions in China: Considering Nonagricultural Sectors Based on Isotopic Source Apportionment.

Isotopic source apportionment results revealed that nonagricultural sectors are significant sources of ammonia (NH3) emissions, particularly in urban areas. Unfortunately, nonagricultural sources have been substantially underrepresented in the current anthropogenic NH3 emission inventories (EIs). Here, we propose a novel approach to develop a gridded EI of nonagricultural NH3 in China for 2016 using a combination of isotopic source apportionment results and the emission ratios of carbon monoxide (CO) and NH3. We estimated that isotope-corrected nonagricultural NH3 emissions were 4370 Gg in China in 2016, accounting for an increase in the total NH3 emissions from 7 to 31%. As a result, compared to the original NH3 EI, the annual emissions of total NH3 increased by 35%. Thus, in comparison to the simulation driven by the original NH3 EI, the WRF-Chem model driven by the isotope-corrected NH3 EI has reduced the model biases in the surface concentrations and dry deposition flux of reduced nitrogen (NHx = gaseous NH3 + particulate NH4+) by 23 and 31%, respectively. This study may have wide-ranging implications for formulating targeted strategies for nonagricultural NH3 emissions controls, making it facilitate the achievement of simultaneously alleviating nitrogen deposition and atmospheric pollution in the future.