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Appropriate nitrogen (N) application increases crop yield, while its unreasonable application results in environmental problem. Determining the appropriate N application rate is the key to sustainable development. Here, the denitrification-decomposition (DNDC) model was used to analyze the effects of N fertilizer on maize yields, economic benefits, nitrate leaching, and nitrous oxide emissions in China. The N application rate for the trade-off between economy and environment at the county scale was further determined. The geodetector model was used to identify the main driving factors and their interactions of the recommended N rate in each agricultural zone. The results showed that the recommended N rate was generally high in the northwest but low in the south, consistent with the spatial patterns of yield potential. However, clay soils with clay ratios greater than 34% in southern China and sandy soils with bulk densities greater than 1.5 g cm

The size-resolved physiochemical properties of aerosols determine their atmospheric lifetime, cloud interactions, and the deposition rate on human respiratory system, however most atmospheric composition studies tend to evaluate these properties in bulk. This study investigated size-resolved constituents of aerosols on mass and number basis, and their droplet activation properties, by coupling a suite of online measurements with an aerosol aerodynamic classifier (AAC) based on aerodynamic diameter (Da) in Pinggu, a suburb of Beijing. While organic matter accounted for a large fraction of mass, a higher contribution of particulate nitrate at larger sizes (Da > 300 nm) was found under polluted cases. By applying the mixing state of refractory black carbon containing particles (rBCc) and composition-dependent densities, aerosols including rBCc were confirmed nearly spherical at Da > 300 nm. Importantly, the number fraction of rBCc was found to increase with Da at all pollution levels. The number fraction of rBC is found to increase from ~3 % at ~90 nm to ~15 % at ~1000 nm, and this increasing rBC number fraction may be caused by the coagulation during atmospheric aging. The droplet activation diameter at a water supersaturation of 0.2 % was 112 ± 6 nm and 193 ± 41 nm for all particles with Da smaller than 1 μm (PM1) and rBCc respectively. As high as 52 ± 6 % of rBCc and 50 ± 4 % of all PM1 particles in number could be activated under heavy pollution due to enlarged particle size, which could be predicted by applying the volume-mixing of substance hygroscopicity within rBCc. As rBCc contributes to the quantity of aerosols at larger particle size, these thickly coated rBC may contribute to the radiation absorption significantly or act as an important source of cloud condensation nuclei (CCN). This size regime may also exert important health effects due to their higher deposition rate.

In this study, an airborne Ka-band Precipitation Cloud Radar (KPR) is used to carry out a cloud observation experiment.By analyzing the attenuation of the snow echo, it is found that during the snowfall, due to the low liquid water content, the KPR attenuation is small on the detection path, and after preliminary comparative analysis, the maximum attenuation correction value is 0.5 dBZ. According to the echo attenuation analysis of mixed precipitation, the melting layer is found to be the key factor affecting the attenuation correction. This study hereby proposes an adaptive echo attenuation correction method based on the melting layer (AEC), and uses the ground-based S-band radar to extract the echo on the aircraft trajectory to verify the correction results. The results show that the echo attenuation correction value above the melting layer is related to the flight position. The aircraft above the melting layer is dominated by ice particles, with small attenuation correction value, the maximum correction amount of 0.13 dBZ; when the aircraft is at and just below the melting layer, a water film is prone to be on the antenna, which leads to serious attenuation of the KPR detection path, with the attenuation correction value 1~2 dBZ. For the precipitation echo below the melting layer, due to the abundant rain and water vapor content, the KPR attenuation is significant with maximum correction value of about 5 dBZ. Compared with the S-band radar, before attenuation correction, the total mean relative error is 15 %, and the correlation coefficient is 0.82; after correction, the total mean relative error is 6 %, and the correlation coefficient is 0.90, indicating the significant improvement of the KPR data quality.

The physical properties of black carbon (BC) including the mass loading, size distribution and mixing state were in-situ characterized by aircraft measurements using a single particle soot photometer (SP2) in the lower troposphere over Beijing area. The flights were conducted in both late spring and winter during the daytime with well-developed planetary boundary layer (PBL). The BC mass in the PBL (BCPBL) in late spring showed no apparent vertical gradient nor correlation with the PBL height (PBLH) due to strong convective mixing; in winter the BCPBL was more concentrated near ground and anti-correlated with the PBLH due to dilution effect of the dominant cleaner northerly air masses at higher altitude. The BC mass loading at height h, C(h) within the PBL can be extended from the surface level (C0) in late spring; for levels above the PBL, C(h) can be parameterized by applying an exponential decline function C(h) = C0*exp(h/hs), with the scale height (hs) of 0.31 ± 0.16 km and 0.66 ± 0.24 km for late spring and winter respectively. This parameterization excluded the profiles for: turbulent conditions when the BC mass was efficiently vented upwards and diluted, expressed as C(h) = C0 up to the top of the PBL; or in periods of strong southerly advection, when the entire column was significantly influenced by regional transport from the polluted south regions. The BC core mass median diameters (MMD) were commonly populated at 205–220 nm in both seasons, with additional mode of MMD ∼195 nm also frequently observed in late spring. The bulk relative coating thickness of BC (coated diameter divided by uncoated core diameter Dp/Dc) in the PBL mostly populated at 2.0–2.2 but at ∼1.2–1.6 in the lower free troposphere (FT). The mass absorption cross section of BC at 550 nm (MAC550), constrained by the SP2 measurements, was largely influenced by the coating thickness, was relatively consistent in the PBL at ∼8.6 m2 g−1, but reduced to 7–7.5 m2 g−1 in the FT or turbulent condition due to decreased coatings. The BC was found to exhibit smaller particle size in the FT but larger in the PBL, which may imply larger BC have been scavenged by low-level clouds. The BC particles trapped in the PBL or regionally transported from polluted region represent the most absorbing element in the particulate matter population and should be particularly considered in evaluating the radiative forcing impact of aerosols over this region.

The size-resolved properties of atmospheric black carbon (BC) importantly determine its absorption capacity and cloud condensation nuclei (CCN) ability. This study reports comprehensive vertical profiles of BC size-related properties over the Beijing area (BJ) and Continental Europe (CE). BC mass loadings over CE were in the range of clean background over BJ. For both planetary boundary layer (PBL) and lower free troposphere, the BC mass median core diameter over BJ during the cold season was 0.21 ± 0.02 μm, larger than the warm season over BJ and CE (0.18 ± 0.01 μm), which may reflect seasonal differences in emissions. The BC coatings were positively correlated with the pollution level, with background BC having a smaller coated count median diameter (0.19 ± 0.01 μm). The modeled absorption enhancement (

Wet scavenging of black carbon (BC) has been subject to large uncertainty, which importantly determines its atmospheric lifetime and indirect forcing impact on cloud microphysics. This study reveals the complex BC‐hydrometeor interactions in mixed‐phase clouds via single particle measurements in the real‐world environment, by capturing precipitation processes throughout cloud formation, cold rain/graupel, and subsequent snow events at a mountain site influenced by anthropogenic sources in wintertime. We found highly efficient BC wet scavenging during cloud formation, with large and thickly coated BC preferentially incorporated into droplets. During snow processes, BC core sizes in the interstitial phase steadily increased. A mechanism was proposed whereby the BC mass within each droplet was accumulated through droplet collision, leading to larger BC cores, which were then released back to the interstitial air through the Wegener‐Bergeron‐Findeisen processes when ice dominated. These results provide fundamental basis for constraining BC wet scavenging.

The transport processes and fate of 137Cs in eastern Chinese seas (ECSs) that consists of the Bohai, Yellow, and East China Seas, have not been well established. In this study, we measured the concentrations of 137Cs in the ECSs water and surface sediments during 2013–2014. Combined with a number of published 137Cs inventory data from drainage basins and sediment accumulation rates in the ECSs, the distribution, sources and budgets of 137Cs in the ECSs were investigated. The 137Cs activity in the water column and surface sediments ranged from 0.03 to 1.92 Bq/m3 and from 0.30 to 5.22 Bq/kg, respectively. No 134Cs signal was observed, suggesting that the Fukushima accident had limited impact on the ECSs during the investigation period. Mass balance of 137Cs suggests that at least 7.4 × 1012 Bq/y of 137Cs imported into the ECSs from the Northwestern Pacific that accounts for 0.7% of the 137Cs transported by the Kuroshio Current, and this value is 5.2 times higher than the sum of atmospheric fallout and total riverine input. The apparent half-lives of 137Cs are estimated to be 15.1 y for the ECS and 7.7 y for the YS. The vertical profiles in the continental shelf edge and the Yangtze River Estuary reveal that the upwelling of the Kuroshio Subsurface Water is the main mechanism of 137Cs import into the ECSs. The high level of 137Cs in oceanic water masses and the low level of 137Cs in riverine and coastal waters make 137Cs a good indicator for tracing water mass movement and interaction. In addition, good correlation between 137Cs activity and mean grain size (φ) indicates that 137Cs can serve as an effective tracer to track dispersal pathways of fine sediments in river-dominated marginal seas.

The representation of volatile organic compound (VOC) deposition and oxidation mechanisms in the context of secondary organic aerosol (SOA) formation are developed in the United Kingdom Chemistry and Aerosol (UKCA) chemistry–climate model. Impacts of these developments on both the global SOA budget and model agreement with observations are quantified. Firstly, global model simulations were performed with varying VOC dry deposition and wet deposition fluxes. Including VOC dry deposition reduces the global annual-total SOA production rate by 2 %–32 %, with the range reflecting uncertainties in surface resistances. Including VOC wet deposition reduces the global annual-total SOA production rate by 15 % and is relatively insensitive to changes in effective Henry's law coefficients. Without precursor deposition, simulated SOA concentrations are lower than observed with a normalised mean bias (NMB) of −51 %. Hence, including SOA precursor deposition worsens model agreement with observations even further (NMB =-66 %). Secondly, for the anthropogenic and biomass burning VOC precursors of SOA (VOCANT∕BB), model simulations were performed by (a) varying the parent hydrocarbon reactivity, (b) varying the number of reaction intermediates, and (c) accounting for differences in volatility between oxidation products from various pathways. These changes were compared to a scheme where VOCANT∕BB adopts the reactivity of a monoterpene (α-pinene), and is oxidised in a single-step mechanism with a fixed SOA yield. By using the chemical reactivity of either benzene, toluene, or naphthalene for VOCANT∕BB, the global annual-total VOCANT∕BB oxidation rate changes by −3 %, −31 %, or −66 %, respectively, compared to when using α-pinene. Increasing the number of reaction intermediates, by introducing a peroxy radical (RO2), slightly slows the rate of SOA formation, but has no impact on the global annual-total SOA production rate. However, RO2 undergoes competitive oxidation reactions, forming products with substantially different volatilities. Accounting for the differences in product volatility between RO2 oxidation pathways increases the global SOA production rate by 153 % compared to using a single SOA yield. Overall, for relatively reactive compounds such as toluene and naphthalene, the reduction in reactivity for VOCANT∕BB oxidation is outweighed by accounting for the difference in volatility of RO2 products, leading to a net increase in the global annual-total SOA production rate of 85 % and 145 %, respectively, and improvements in model agreement (NMB of −46 % and 56 %, respectively). However, for benzene, the reduction in VOCANT∕BB oxidation is not outweighed by accounting for the difference in SOA yield pathways, leading to a small change in the global annual-total SOA production rate of −3 %, and a slight worsening of model agreement with observations (NMB =-77 %). These results highlight that variations in both VOC deposition and oxidation mechanisms contribute to substantial uncertainties in the global SOA budget and model agreement with observations.

A numerical simulation and a wind tunnel experiment are performed to investigate the flow field and pollutant dispersion in a two dimensional (2-D) ideal urban street canyon with roofs installed in a viaduct at different heights. Two typical roof shapes are taken into consideration: double flat (DF) and double triangular (DT). The simulation results show that when the height of the viaduct is at 0.875H–0.98H for DF and at 0.71H–0.988H for DT, the main flow field in the canyon will be reversed compared to initial flow field. This reversing phenomenon will aggravate pollution for DF and significantly mitigate pollution for DT compared to levels without a viaduct. The wind tunnel experiment is qualitatively consistent with the numerical simulation results which indicates that this reversing phenomenon is not just theoretical. A mechanism is proposed whereby the viaduct obstructing airflow is the key reason for the flow field reversion.

To investigate the transport and formation mechanism of pollution in Beijing, this study explored the vertical profiles of aerosol properties using aircraft measurement during a regional transport (RT) pollution event from 10th to 12th December 2016. The aerosol chemical composition and size distribution were characterized. Different vertical structures exhibited during three periods (defined as before RT, during RT, and after RT) for this pollution event. Before RT, PM2.5 and black carbon (BC) mass loading were at low level in the mixing layer (ML) when the clean northerly air mass dominated. During RT, an elevated aerosol layer, in which BC and PM2.5 mass concentrations were about 1.5 times higher than that at the ground level, was found in the upper ML (at 400–900 m) over Beijing. This elevated aerosol layer was advected by the prevailing southwesterly air mass which transported the pollutants from the intensively polluted southwestern region over Beijing. These aerosols through RT featured with pronounced secondary compositions and large coatings on BC particles. After RT, the pollutants were significantly diluted by the prevailing NW air mass, whereas the aerosol concentration almost maintained in the near surface, leading to notable vertical gradient. The continued surface pollution may result from the low wind speed and secondary aerosol formation in the next day. This study suggests that only the ground observation could not fully explain the pollution event, but the variation of vertical structure of aerosol properties should be considered to elucidate the formation mechanism of pollution over Beijing.

In this study, we investigated the levels of 12 priority polycyclic aromatic hydrocarbons (PAH12) pollutants, bioaccessible PAH12, and sorption sink for PAH12 by a silicone sheet of indoor dust samples, which were collected from teachers' offices (n = 17), students' offices (n = 17), laboratory (n = 11), and experimental center (n = 9), using an in vitro digestive model. In PAH12, bioaccessible PAH12, and sorption sink PAH12, benzo[b]fluoranthene (BbF), phenanthrenes (Phe), and fluoranthene (FLA) were labeled respectively the most significant PAHs (6.61 ± 4.42 μg/g, 0.16 ± 0.11 μg/g, and 0.08 ± 0.06 μg/g) after indoor dust ingestion, whereas the proportions of anthracene (Ant), benzo(g,h,i)perylene (BghiP), and BghiP (0.34 ± 0.17, 0.03 ± 0.03 and 0.01 ± 0.01 μg/g) were low. Based on benzo[a]pyrene- equivalent carcinogenic concentrations, the mean daily exposure of bioaccessible PAH12 and sorption sink for PAH12 by indoor dust ingestion was 4.07 × 10−3 ± 1.73 × 10−3 and 3.23 × 10−3 ± 1.36 × 10−3 μg/day in the experimental center; 4.01 × 10−3 ± 2.05 × 10−3 and 1.46 × 10−3 ± 6.72 × 10−4 μg/day in students' offices; 8.25 × 10−4 ± 2.33 × 10−4 and 5.15 × 10−4 ± 1.37 × 10−4 μg/day in laboratory; and 7.05 × 10−4 ± 4.12 × 10−5 and 2.82 × 10−4 ± 4.36 × 10−5 μg/day in teachers' offices, respectively. Our results indicated that the passive transfer fraction of PAH12 (44.07%–67.36% in this case) is therefore large and needs to be considered in exposure and risk assessments.

Content caching in the device-to-device (D2D) cellular networks can be utilized to improve the content delivery efficiency and reduce traffic load of cellular networks. In such cache-enabled D2D cellular networks, how to cache the diversity contents in the multiple cache-enabled mobile terminals, namely, the caching deployment, has a substantial impact on the network performance. In this paper, a user preference aware caching deployment algorithm is proposed for D2D caching networks. First, the definition of the user interest similarity is given based on the user preference. Then, a content cache utility of a mobile terminal is defined by taking the transmission coverage region of this mobile terminal and the user interest similarity of its adjacent mobile terminals into consideration. A general cache utility maximization problem with joint caching deployment and cache space allocation is formulated, where the special logarithmic utility function is integrated. In doing so, the caching deployment and the cache space allocation can be decoupled by equal cache space allocation. Subsequently, we relax the logarithmic utility maximization problem, and obtain a low complexity near-optimal solution via a dual decomposition method. Compared with the existing caching placement methods, the proposed algorithm can achieve significant improvement on cache hit ratio, content access delay, and traffic offloading gain.

Iodirne-129 is useful for tracking water mass movement in the ocean. In this study, the concentration of iodine isotopes in seawater of the East China Sea (ECS) in October 2013 were analyzed to investigate the spatial and vertical distribution of 129I and 127I to understand water mass exchange. Results showed that the 129I/127I atomic ratios varied with the water mass, with higher values of (10-20) × 10-11 in the coastal regions and lower values of b8 × 10−11 offshore. Inventories of 129I were estimated to be (0.23–1.7) × 1012 atoms m−2 (n = 18) in upper 100 m waters, which is comparable to those of other regions without being contaminated by the nuclear accidents or nuclear reprocessing facilities. The total amount of 129I in the ECS water column was estimated to be 88 g in which over 90% is attributed to the oceanic input (e.g., West Pacific) via the Kuroshio Current (KC). The contributions of 129I from Changjiang (Yangtze River) terrestrial watershed (b7.5%) and atmospheric fallout (b2.7%) were small. Those from the Fukushima accident were negligible during this investigation. The 129I/127I ratios versus salinity distribution showed the range and stratification of the Changjiang, Yellow Sea, and KC waters in the ECS. Our study shows that the Changjiang fresh water could be transported to the North Jiangsu coast in October; the Taiwan Warm Current water could intrude to Northern part of the Changjiang Estuary (32°N). Besides, our results suggest that the 129I/127I profile is useful to indicate the seawater mixing process in ocean marginal systems.

The epigenetic modification of DNA or RNA may have relationship with the development of diabetic nephropathy (DN). We designed to develop a liquid chromatography mass spectrometry (LC–MS) coupled with mobile phase additive sensitization method for the analysis of the dissociative epigenetic modified nucleosides in serum of patients from different periods of DN with the health comparison. Serum samples were collected from 43 healthy volunteers and 156 patients, which divided into four groups. A succinic acid enhanced LC–MS/MS strategy was developed for the quantitative analysis of seven nucleosides in serum samples. The signal intensity of seven nucleosides increased three to seven times, respectively. A series of statistical analysis were carried out to demonstrate the dynamic changes of modified nucleosides in four groups. This method showed good specific, accuracy, and stability. The results were calibrated and presented through the formation of m6A/C, I/C, 5-mdC/C, 5-mC/C, pseU/U to eliminate the individual and age differences. The m6A/C, I/C, and pseU/U were found having the dynamic changes in four groups (p

The oxidation of polycyclic aromatic hydrocarbons (PAHs) determines their lifetime, toxicity and consequent environmental and climate impacts. The residential solid fuel burning composes of a substantial fraction of PAH emissions; however, their oxidation rate is yet to be explicitly understood, which is complicated by the contrasting emission factors under different combustion conditions and their subsequent evolution in the atmosphere. Here we used a plume evolution chamber using ambient oxidants to simulate the evolution of residential solid fuel burning emissions under real-world solar radiation, and then to investigate the oxidation process of the emitted PAHs. Contrasting oxidation rate of PAHs was found to be influenced by particles with or without presence of substantial amount of black carbon (BC). In the flaming burning phase, which contained 46% of BC mass fraction and 8% of organic aerosol (OA) internally mixed with BC, the larger PAHs (with 4-7 rings) was rapidly oxidized 12% for every hour of evolution under solar radiation; however, the larger PAHs from smoldering phase tended to maintain unmodified during the evolution, when 95% of OA was externally mixed with only minor fraction of BC (5%). This may be ascribed to the complex morphology of BC, allowing more exposure for the internally-mixed OA to the oxidants; in contrast with those externally-mixed OA which was prone to be coated by condensed secondary substances. This raises an important consideration about the particle mixing state in influencing the oxidation of PAHs, particularly the coating on PAHs which may extend their lifetime and environmental impacts.

Residential coal combustion (RCC) emission exhibited obvious daily variation, while no real-time estimation of air pollutants from RCC has been reported, as the shortages of corresponding activity dataset and emission factors with high time resolution. A real-time monitoring platform for RCC emission was established. Hourly emission factors of 18 typed of TEs from eleven kinds of chunk coals and nine kinds of honeycomb coals burning in China were obtained. The monthly and hourly coal consumption amounts were calculated with reference and our field survey. Then the hourly TEs emission inventories from RCC were established in China. GEOS-Chem and Risk Quotients Models were utilized to map the spatialized health risks of hazardous elements, including the gridded hazard index and carcinogenic risk. The result indicated that the EFs of TEs would be underestimated if the tests only consider flaming conditions. Cu, K, Ca, Zn, and Co were the top five elements from RCC, with corresponding emission amounts as 1397.7, 1054.0, 676.0, 623.5 and 420 tons in 2017, respectively. K, Ti, Fe, Sn, and Sb showed hourly peak values under flaming dominated periods, accounting for 48.2%, 45.9%, 31.8%, 42.8%, and 33.8% of their daily emissions. Other elements (e.g., V, Co, As, Hg and Pb) exhibited higher emissions under smoldering dominated period in nighttime, accounting for 22.2%, 32.9%, 27.6%, 34.7%, and 28.4% of their daily emissions. TEs emission from RCC closely follows the habits of human daily cooking and heating activity. The national HI were lower than the acceptable level (HI ≤ 1) except Sichuan Province (up to 1.2). Higher carcinogenic risks (≥1 × 10-6) occurred in parts of Sichuan, Shanxi, Hunan and Hubei, which were up to 2.0 × 10-5. The high-resolution TEs emission inventories could be useful for future modeling works on the formation and evolution of air pollution and are helpful for human exposure assessment.

Cloud particles have different shapes in the atmosphere. Research on cloud particle shapes plays an important role in analyzing the growth of ice crystals and the cloud microphysics. To achieve an accurate and efficient classification algorithm on ice crystal images, this study uses image-based morphological processing and principal component analysis, to extract features of images and apply intelligent classification algorithms for the Cloud Particle Imager (CPI). Currently, there are mainly two types of ice-crystal classification methods: one is the mode parameterization scheme, and the other is the artificial intelligence model. Combined with data feature extraction, the dataset was tested on ten types of classifiers, and the highest average accuracy was 99.07%. The fastest processing speed of the real-time data processing test was 2,000 images/s. In actual application, the algorithm should consider the processing speed, because the images are in the order of millions. Therefore, a support vector machine (SVM) classifier was used in this study. The SVM-based optimization algorithm can classify ice crystals into nine classes with an average accuracy of 95%, blurred frame accuracy of 100%, with a processing speed of 2,000 images/s. This method has a relatively high accuracy and faster classification processing speed than the classic neural network model. The new method could be also applied in physical parameter analysis of cloud microphysics.

The atmospheric chemistry in complex air pollution remains poorly understood. In order to probe how environmental conditions can impact the secondary organic aerosol (SOA) formation from biomass burning emissions, we investigated the photooxidation of 2,5-dimethylfuran (DMF) under different environmental conditions in a smog chamber. It was found that SO

The physical and chemical properties of black carbon (BC) and organic aerosols are important for predicting their radiative forcing in the atmosphere. During the Soot Aerodynamic Size Selection for Optical properties (SASSO) project and a EUROCHAMP-2020 transnational access project, different types of light absorbing carbon were studied, including BC from catalytically stripped diesel exhaust, a flame burner, a colloidal graphite standard (Aquadag), and from controlled flaming wood combustion. Brown carbon (BrC) was also investigated in the form of organic aerosol emissions from wood burning (pyrolysis and smouldering) and from the nitration of secondary organic aerosol (SOA) proxies produced in a photochemical reaction chamber. Here we present insights into the physical and chemical properties of the aerosols, with optical properties being presented in subsequent publications. The dynamic shape factor (χ) of BC particles and material density (ρm) of organic aerosols were investigated by coupling a charging-free Aerodynamic Aerosol Classifier (AAC) with a Centrifugal Particle Mass Analyzer (CPMA) and Scanning Mobility Particle Sizer (SMPS). The morphology of BC particles was captured by transmission electron microscopy (TEM). For BC particles from the diesel engine and flame burner emissions, the primary spherule sizes were similar, around 20 nm. With increasing particle size, BC particles adopted more collapsed/compacted morphologies for the former source but tended to show more aggregated morphologies for the latter source. For particles emitted from the combustion of dry wood samples, the χ of BC particles and the ρm of organic aerosols were observed in the ranges 1.8–2.17 and 1.22–1.32 g/cm3, respectively. Similarly, for wet wood samples, the χ and ρm ranges were 1.2–1.85 and 1.44–1.60 g/cm3, respectively. Aerosol mass spectrometry measurements show no clear difference in mass spectra of the organic aerosols in individual burn phases (pyrolysis or smouldering phase) with the moisture content of the wood samples. This implies that the effect moisture has on the organic chemical profile of wood burning emissions is through changing the durations of the different phases of the burn cycle, not through the chemical modification of the individual phases. In this study, the incandescence signal of a Single Particle Soot Photometer (SP2) was calibrated with three different types of BC particles and compared with that from an Aquadag standard that is commonly used to calibrate SP2 incandescence to a BC mass. A correction factor is defined as the ratio of the incandescence signal from an alternative BC source to that from the Aquadag standard, and took values of 0.82 (or 0.79), 0.88 and 0.84–0.91 for the BC particles emitted from the diesel engine running under hot (or cold idle) conditions, the flame burner and wood combustion, respectively. These correction factors account for differences in instrument response to BC from different sources compared to the standardised Aquadag calibration and are more appropriate than the common value of 0.75 recommended by Laborde et al. (2012b) when deriving the mass concentration of BC emitted from diesel engines. Quantifying the correction factor for many types of BC particles found commonly in the atmosphere may enable better constraints to be placed on this factor depending on the BC source being sampled, and thus improve the accuracy of future SP2 measurements of BC mass concentrations.

Accurate source markers, source profiles and species-based emission factors (EFs) are currently the key limitations for source apportionment and emission inventory researches. Fine particles (PM2.5) were collected from stack gases of eight types of stationary sources with a dilution sampling system. The mass percentages and EFs of 89 kinds of chemical species in PM2.5 including water-soluble ions, elements, carbonaceous species and molecular organic species were obtained. Results showed that water-soluble ions (8%–54%) and elements (5%–45%) were the dominant chemical species. Palmitic acid (0.19%–0.62%) and stearic acid (0.21%–0.59%) were the most abundant organic species. PM2.5 source profiles of the eight sources were different from each other with the coefficient of divergence values all higher than 0.4. The addition of organic species could help to further distinguish them. The indicatory chemical components and specific species ratios were obtained by both a statistical equation and randomForest. These indicatory chemical components (e.g. F− for glass factory) and species ratios (e.g. K+/Mg2+ & OC/Mg for pharmaceutical factory) improved the current knowledges of their indicatory performance in source identification of ambient PM2.5. The EFs of PM2.5 from the eight stationary sources ranged from 0.019 to 51.6 kg t−1 of fuel used. The EFs of PM2.5 from the pharmaceutical factory were about 70–2600 times higher than other seven types of sources due to the lack of dust-removing devices. Certain EFs measured in this study were about 10–36,000 times lower than corresponding EFs estimated in previous studies which didn't perform field measurements, indicating the necessity for improving emission inventories continuously. This study contributes to identifying emission sources of PM2.5 especially for subtypes of stationary sources and to establishing species-based emission inventories.

Mitigating environmental pollution and sustaining grain production have been foundational issues in sustainable development, however, ascertaining the optimal balance remains poorly investigated. This study used the Soil and Water Assessment Tool (SWAT) model to simulate crop growth and nitrogen loss, established the mapping relationship between nitrogen input to yield and water quality, and proposed a general method to determine a nitrogen application strategy for high yield and low pollution at a basin scale. Lake Xiaoxingkai basin, which is the primary maize producing area in China as well as an internationally important wetland distribution area, was used as a case study. First, we designed application scenarios for 10 base fertilizers (B1–B10) and 10 topdressing fertilizers (T1–T10) and evaluated their combined effects of maize growth to identify the critical nitrogen fertilizer rates determined under fixed and dynamic base/topdressing ratios. Then, the critical base and topdressing fertilizer rates were determined. Based on the mapping relationship between nitrogen fertilizer rate and nitrogen loss, we then revealed water quality at the basin outlet under the critical base and topdressing fertilizer rates. Finally, we proposed alternative nitrogen application strategies for high yield and low pollution while considering the different preferences of decision-makers for the economy, agriculture, and environment. We found that adjusting the ratio of base to topdressing fertilizer may create a win-win situation for agriculture and the environment, which will provide a scientific basis for sustainable development.

Primary organic aerosols (POAs) are a major component of PM2.5 in winter polluted air in the North China Plain (NCP), but our understanding of the atmospheric aging processes of POA particles and the resulting influences on their optical properties is limited. As part of the Atmospheric Pollution and Human Health in a Chinese Megacity (APHH-Beijing) program, we collected airborne particles at an urban site (Beijing) and an upwind rural site (Gucheng, Hebei province) in the NCP during 13–27 November 2016 for microscopic analyses. We confirmed that large numbers of light-absorbing spherical POA (i.e., tarball) and irregular POA particles with high viscosity were emitted from domestic coal and biomass burning at the rural site and were further transported to the urban site during regional wintertime hazes. During the heavily polluted period (PM2.5 > 200 µg m−3), more than 60 % of these burning-related POA particles were thickly coated with secondary inorganic aerosols (named as core–shell POA–SIA particles) through the aging process, suggesting that POA particles can provide surfaces for the heterogeneous reactions of SO2 and NOx. As a result, during the heavily polluted period, their average particle-to-core diameter ratios at the rural and urban sites increased to 1.60 and 1.67, respectively. Interestingly, we found that the aging process did not change the morphology and sizes of POA cores, indicating that the burning-related POA particles are quite inert in the atmosphere and can be transported over long distances. Using Mie theory we estimated that the absorption capacity of these POA particles was enhanced by ∼ 1.39 times in the heavily polluted period at the rural and urban sites due to the “lensing effect” of secondary inorganic coatings. We highlight that the lensing effect on burning-related POA particles should be considered in radiative forcing models and authorities should continue to promote clean energy in rural areas to effectively reduce primary emissions.

Secondary organic aerosol (SOA) produced by atmospheric oxidation of primary emitted precursors is a major contributor to fine particulate matter (PM(2.5)) air pollution worldwide. Observations during winter haze pollution episodes in urban China show that most of this SOA originates from fossil-fuel combustion but the chemical mechanisms involved are unclear. Here we report field observations in a Beijing winter haze event that reveal fast aqueous-phase conversion of fossil-fuel primary organic aerosol (POA) to SOA at high relative humidity. Analyses of aerosol mass spectra and elemental ratios indicate that ring-breaking oxidation of POA aromatic species, leading to functionalization as carbonyls and carboxylic acids, may serve as the dominant mechanism for this SOA formation. A POA origin for SOA could explain why SOA has been decreasing over the 2013–2018 period in response to POA emission controls even as emissions of volatile organic compounds (VOCs) have remained flat.

Microplastics have become global emerging issue and received widespread attention in recent years. Due to their chemical persistence, plastic particles can be broken into smaller items but accumulated for long time in the environment like sediment. However, limited by current detection technologies, the distribution and characteristics of small-sized microplastics in coastal sediment remain uncertain. In this study, we established a new method based on micro-Raman spectroscopy for detecting small-sized microplastics, namely multipoint confocal micro-Raman spectrum scanning (MCmRSS). The MCmRSS was first applied in detecting microplastics in the sediment samples collected from three bays of the East China Sea. The minimum size of microplastics was 4 μm and average microplastics concentration was 91 ± 55 items /g dry weight sediment, with fragment and polyethylene as the most common shape and polymer type, respectively. The spatial variation of microplastics was in accordance with the strength of coastal human activities and marine dynamics. In all the microplastic items, the small-sized ones (10 μm) accounted for 67%; and the relationship between microplastic concentration and its size followed a power-exponential equation. Compared with previous studies, the number of microplastics in coastal sediments detected by the MCmRSS increased by 2 orders of magnitude, which was benefited from the advantages of multipoint scanning in the fixed identification areas and high resolution of micro-Raman spectrum. Our findings would summon the re-evaluation of the potential risks of small-sized microplastics in the coastal environment.

Levoglucosan (LG) emitted from non-biomass burning (non-BB) sources has given rise to biased or even unreasonable source identification results when adopting LG as a distinct marker of biomass burning (BB). The estimation of LG emission and its spatiotemporal variation for various sources are the keys to reducing uncertainty. This study first developed a LG emission inventory for China from 25 sub-type sources belonging to eight categories, with a 3 km × 3 km spatial resolution and monthly distribution. The total LG emission in 2014 was 145.7 Gg. Domestic BB and open BB contributed 39.2 and 34.3% of the total emission. Non-BB sources, including municipal solid waste burning (9.7%), firework burning (9.6%), meat cooking (5.4%), domestic coal burning (1.5%), ritual item burning (0.2%), and industrial coal burning (0.1%), contributed to 26.5% of the total emission. LG emission varied spatially and temporally. Non-BB sources have a significant spatiotemporal impact on BB source contributions, even in high BB emission regions or in sowing, harvesting, and winter heating seasons. The local BB contributions have been substantially overestimated by 4.28-369% in previous studies, wherein LG was solely referred to as the BB source. By 2018, LG emission from BB might decrease to 63.9% of its total emission. This high-resolution LG emission inventory can be greatly useful for source identification studies in China. It also supports future research on the modeling of smoke aging and pollution control.

Additional file 2: Fig. S1. Relative expression levels of selected genes determined by qRT-PCR.

The hygroscopicity and ability of aerosol particles to act as cloud condensation nuclei (CCN) is important in determining their lifetime and role in aerosol-cloud interactions, thereby influencing cloud formation and climate. Previous studies have used the aerosol hygroscopic properties measured at the ground to evaluate the influence on cloud formation in the atmosphere, which may introduce uncertainty associated with aerosol hygroscopicity variability with altitude. In this study, the CCN behaviour and hygroscopic properties of daily filter collections of PM2.5 from three different heights (8, 120, 260 m) on a tower in Beijing were determined in the laboratory using water, water/methanol and methanol as the atomization solvents. Whilst there was substantial temporal variability in particle concentration and composition, there was little obvious difference in aerosol CCN and hygroscopic behaviour at different heights, although the planetary boundary layer height (PBLH) reduced to below the tower height during the nighttime, suggesting that use of surface hygroscopicity measurements is sufficient for the estimation of aerosol particle activation in clouds. Additionally, the critical coating thickness (in terms of mass ratio of coating/refractory BC, MRc) defining the BC transition between being hydrophobic to hydrophilic, was determined by combining hygroscopic tandem differential mobility analyser (H-TDMA), centrifugal particle mass analyzer (CPMA) and single particle soot photometer (SP2) measurements. The MRc of 250 nm BC-containing particles increased from a background value of between 0.8 and 1.6 to around 4.6 at the onset of the growth event of nanoparticles, decreasing monotonically back to the background level as the event progressed. This indicates that large particles do not act as an effective pre-existing condensation sink of the hygroscopic vapours during the nanoparticle growth events, leading to the 250 nm BC particles requiring more coating materials to transition between being hydrophobic and hydrophilic. These findings show that large particles may be less important in suppressing the new particle formation and subsequent growth in the atmosphere.

Commercial shipping is considered as an important source of air pollution and cloud condensation nuclei (CCN). To assess the climatic and environmental impacts of shipping, detailed characterization of ship plumes near the point of emission and understanding of ship plume evolution further downwind are essential. This airborne measurement study presents the online characterization of particulate phase ship emissions in the region of Western Europe in 2019 prior to new international sulfur emission controls becoming enacted. More than 30 ships from both the sulfur emission control area (SECA) in the English Channel and the open sea (OS) are measured and compared. Ships within the SECA emitted much less sulfate (SO4) compared with those at OS. When shifted to a lower apparent fuel sulfur content (FSC) at similar engine loads, the peak of the fresh ship emitting the particle number size distribution shifted from around 60-80 nm in diameter to below 40 nm in diameter. The emission factors (EFs) of sulfate are predicted to decrease by around 94% after the 2020 regulation on ship sulfur emission in the open ocean. The EFs of refractory black carbon (rBC) and organic compounds (Org) do not appear to be directly affected by the lower sulfur contents. The total number concentration for condensation nuclei (CN) >2.5 nm and >0.1 μm are predicated to be reduced by 69 and 56%, respectively. Measured plume evolution results indicate that the S(IV) to S(VI) conversion rate was around 23.4% per hour at the beginning of plume evolution, and the CCN and CN >2.5 nm ratio increased with plume age primarily due to condensation and coagulation. We estimate that the new sulfur emission regulation will lead to a reduction of more than 80% in CCN from fresh ship emissions. The ship-emitted EFs results presented here will also inform emission inventories, policymaking, climate, and human health studies.

Currently solving the severe particle pollution in autumn and winter is the key to further improve the air quality of China. The source contributions and transboundary transport of fine particles (PM2.5) in pollution episodes are closely related to large-scale or synoptic-scale atmospheric circulation. Under different synoptic conditions, how to effectively reduce emissions to control haze pollution is rarely reported. In this study, we classify the synoptic conditions over Central China from 2013 to 2018 by using Lamb-Jenkension method and the NCEP/NCAR FNL operational global analysis data. The effectiveness of emission control to reduce PM2.5 pollution during winter haze episodes under potential synoptic controls is simulated by GEOS-Chem model. Among the ten identified synoptic patterns, four types account for 87 % of the total pollution days. Two typical synoptic modes of them are characterized by small surface wind speed and stable weather conditions/high relative humidity (A/C-type) over Central China due to a high-pressure system/a southwest trough low-pressure system, blocking pollutants dispersion. Sensitivity simulations show that these two heavy pollution processes are mainly contributed by local emission sources with ~82 % for A-type and ~85 % for C-type, respectively. The other two patterns lead to pollution of transportation characteristics affected by northerly/southerly winds (NW/SW-type), carrying air pollution from northern/southern China to Central China. The contribution of pollution transportation from North/South China is 36.9 %/7.6 % of PM2.5 and local emission sources contribute 41 %/69 %. We also estimate the effectiveness of emission reduction in these four typical severe pollution synoptic processes. By only reducing SO2 and NOx emission and not controlling NH3, the enhanced nitrate counteracts the effect of sulfate reduction on PM2.5 mitigations with less than 4% decrease in PM2.5. In addition, to effectively mitigate haze pollution in NW/SW-type synoptic controlled episodes, local emission control actions should be in coordination with regional collaborative actions.

Light-absorbing carbonaceous aerosols (LACs), including black carbon and light-absorbing organic carbon (brown carbon, BrC), have an important role in the Earth system via heating the atmosphere, dimming the surface, modifying the dynamics, reducing snow/ice albedo, and exerting positive radiative forcing. The lifecycle of LACs, from emission to atmospheric evolution further to deposition, is key to their overall climate impacts and uncertainties in determining their hygroscopic and optical properties, atmospheric burden, interactions with clouds, and deposition on the snowpack. At present, direct observations constraining some key processes during the lifecycle of LACs (e.g., interactions between LACs and hydrometeors) are rather limited. Large inconsistencies between directly measured LAC properties and those used for model evaluations also exist. Modern models are starting to incorporate detailed aerosol microphysics to evaluate transformation rates of water solubility, chemical composition, optical properties, and phases of LACs, which have shown improved model performance. However, process-level understanding and modeling are still poor particularly for BrC, and yet to be sufficiently assessed due to lack of global-scale direct measurements. Appropriate treatments of size- and composition-resolved processes that influence both LAC microphysics and aerosol–cloud interactions are expected to advance the quantification of aerosol light absorption and climate impacts in the Earth system. This review summarizes recent advances and up-to-date knowledge on key processes during the lifecycle of LACs, highlighting the essential issues where measurements and modeling need improvement.

Primary organic aerosol (POA) is a major component of PM2.5 in the winter polluted air in the North China Plain (NCP), but our understanding on the atmospheric aging process of POA particles and the resulting influences on their optical properties is limited. As part of the Atmospheric Pollution and Human Health in a Chinese Megacity (APHH-Beijing) programme, we collected airborne particles at an urban site (Beijing) and an upwind rural site (Gucheng, Hebei province) in the NCP during 13–27 November 2016 for microscopic analyses. We confirmed that a distinct group of spherical or irregular POA particles with high viscosity, defined as primary organic tar (POT) particles, was emitted from the domestic coal and biomass burning at the rural site and was further transported to the urban site during the regional wintertime hazes. During the heavily polluted period (PM2.5 > 200 μg m−3), more than 60 % of the POT particles were thickly coated with secondary inorganic aerosols (named as core–shell POT-SIA particle) through the aging process, suggesting that POT particles can provide surfaces for the heterogeneous reactions of SO2 and NOx. As a result, their average particle-to-core ratios at the rural and urban sites in the heavily polluted period increased to 1.60 and 1.67, respectively. Interestingly, we found that the aging process did not change the morphology and sizes of the POT cores, indicating that POT particles are quite inert in the atmosphere and can be transported long distances. We using the Mie theory estimated that the light absorption of individual POT particles was enhanced by ~ 1.39 times in the heavily polluted period at the rural and urban sites due to the lensing effect of secondary inorganic coatings. We highlight that the lensing effect on POT particles should be considered in radiative forcing models and the governments should continue to promote clean energy in rural areas to effectively reduce primary emissions.