Impact of agricultural waste burning in the Shandong Peninsula on carbonaceous aerosols in the Bohai Rim, China

Application of Biomass Smoldering for Rural Building Heating in China: Strengths and Challenges

Biomass smoldering for rural building heating could be a potential choice for bioenergy utilization in China to reduce the pollution caused by agroresidues open burning and to satisfy the increased demand of rural building heating. Its strengths include low pretreatment, transportation, and storage fees of fuel; ease of operation; good fertilizer characteristics of ash; use of latent heat of water vapor; pollution reduction; reduction of pests, weeds, and plant diseases on the farm; etc. However, controls of the burn rate and the gas emission are two challenges of the application, and related solutions of these challenges are discussed.

Nitrogen isotopic composition of NOx from residential biomass burning and coal combustion in North China

Stable nitrogen isotope (δ¹⁵N) technology has often been used as a powerful tool to separate nitrogen oxides (NO_x) produced by residential combustion (i.e., biomass burning and coal combustion) from other sources. However, the insufficient measurement of δ¹⁵N-NO_x fingerprints of these emissions limits its application, especially in North China where residential emissions are significant. This study conducted combustion experiments to determine the δ¹⁵N-NO_x of typical residential fuels in North China, including ten biomass fuels and five types of coal. The results showed that the δ¹⁵N of biomass varied between -6.9‰ and 2.3‰, which was lower than the δ¹⁵N of residential coal (-0.2‰-4.6‰). After combustion, the δ¹⁵N of biomass residues increased greatly, while that of coal residues showed no significant upward trend (p > 0.05). The δ¹⁵N-NO_x produced by biomass burning ranged from -5.6‰ to 3.2‰ (-0.4‰ ± 2.4‰), showing a significant linear relation with δ¹⁵N-biomass. Comparatively, the δ¹⁵N-NO_x derived from residential coal combustion was much higher (16.1‰ ± 3.3‰), ranging from 11.7‰ to 19.7‰. It was not well correlated with δ¹⁵N-coal, and only slightly lower than the estimated δ¹⁵N-NO_x of industrial coal combustion (17.9‰, p > 0.05). These observations indicate that the δ¹⁵N-NO_x of residential coal combustion is a result of the mixture of thermal- and fuel-released NO_x. Based on the isotopic characteristics observed in this study, we analyzed the reported δ¹⁵N-NO_x, and provided more statistically robust δ¹⁵N-NO_x distributions for biomass burning (1.3‰ ± 4.3‰; n = 101) and coal combustion (17.9‰ ± 3.1‰; n = 26), which could provide guidance for scientific studies aiming to quantify the origin of NO_x in North China and in other regions.

Source Apportionment and Toxic Potency of PM2.5-Bound Polycyclic Aromatic Hydrocarbons (PAHs) at an Island in the Middle of Bohai Sea, China

Polycyclic aromatic hydrocarbons (PAHs) have attracted more attention because of their high atmospheric concentration and toxicity in recent decades. In this study, a total of 60 PM2.5 samples were collected from Beihuangcheng Island in Bohai Sea, China, from August 2017 to March 2018 for analyzing 16 congeners of PAHs (Σ16PAHs). Sources of PAHs were apportioned by a positive matrix factorization (PMF) model and the carcinogenic risk due to exposure to the PAHs was estimated by the toxicity equivalent of BaP (BaPeq). The results showed that the average concentration of Σ16PAHs was 35.3 ± 41.8 ng/m3. The maximum concentration of Σ16PAHs occurred in winter, followed by spring and autumn, and summer. The PMF modeling apportioned the PAHs into four sources, coal combustion, biomass burning, vehicle exhaust, and petroleum release, contributing 43.1%, 25.8%, 24.7%, and 6.39%, respectively. The average ΣBaPeq concentration was 2.32 ± 4.95 ng/m3 during the sampling period, and vehicle exhaust was the largest contributor. The finding indicates that more attention should be paid to reduce the emissions from coal combustion and vehicle exhaust because they were the largest contributors to the PAH concentration in PM2.5 and ΣBaPeq concentration, respectively.

Exploring source footprint of Organophosphate esters in the Bohai Sea, China: Insight from temporal and spatial variabilities in the atmosphere from June 2014 to May 2019

Organophosphate esters (OPEs) are still produced and used in large quantities in the world-wide, and the environmental burden and behavior have generated widespread concern, especially in some large-scale waterbodies. This study conducted a comprehensive assessment on the temporal and spatial variabilities and budget of OPEs to trace the source for the Bohai Sea (BS), based on a 5-year seasonal monitoring campaign (June 2014 to May 2019) of 12 atmospheric sites around the BS and our previous studies. The average concentration of Σ₁₀OPEs in atmosphere during the sampling period was 7.65 ± 6.42 ng m^-3, and chlorinated OPEs were the major compounds. The Seasonal-Trend decomposition procedure based on Loess (STL) analyzed that during the 5-year sampling period, the atmospheric concentrations of Σ₁₀OPEs had a slightly increasing trend with a rate of + 0.092 ng m^-3 yr^-1, and the seasonal concentrations had a distinct seasonal distribution. The highest concentration of Σ₁₀OPEs was observed at the sampling site of Dalian, followed by Tianjin, Yantai, and Beihuangcheng. The estimation of the fugacity ratios and air-water gas exchange fluxes established that the concentration levels of two major components of chlorinated OPEs (tris-(2-chloroethyl) phosphate (TCEP) and tris-(1-chloro-2-propyl) phosphate (TCPP)) in the atmosphere were dominated by their volatilization from BS's seawater (1.24 ± 0.46 t yr^-1 for TCEP and 5.15 ± 2.15 t yr^-1 for TCPP), with 73% deriving from the coastal seawater. The budget assessment suggested that the volatile fluxes of TCEP and TCPP accounted for 8% and 29% of their storages (15.6 ± 5.32 t for TCEP and 17.6 ± 6.70 t for TCPP) in the BS seawater, which were mainly contributed by continental river input (20% for TCEP and 42% for TCPP). The efforts indicated that river inputs of TCEP and TCPP needed to be paid more attention for the improvement of environmental quality of the BS.

Potential Risks of PM2.5-Bound Polycyclic Aromatic Hydrocarbons and Heavy Metals from Inland and Marine Directions for a Marine Background Site in North China

Ambient PM_2.5-bound ions, OC, EC, heavy metals (HMs), 18 polycyclic aromatic hydrocarbons (PAHs), 7 hopanes, and 29 n-alkanes were detected at Tuoji Island (TI), the only marine background atmospheric monitoring station in North China. The annual PM_2.5 average concentration was 47 ± 31 μg m^-3, and the average concentrations of the compositions in PM_2.5 were higher in cold seasons than in warm seasons. The cancer and non-cancer risks of HMs and PAHs in cold seasons were also higher than in warm seasons. BaP, Ni, and As dominated the ∑HQ (hazard quotient) in cold seasons, while the non-carcinogenic risk in warm seasons was mainly dominated by Ni, Mn, and As. The ILCR (incremental lifetime cancer risk) values associated with Cr and As were higher in the cold season, while ILCR-Ni values were higher in the warm season. The backward trajectory was calculated to identify the potential directions of air mass at TI. Through the diagnostic ratios of organic and inorganic tracers, the sources of particulate matter in different directions were judged. It was found that ship emissions and sea salt were the main sources from marine directions, while coal combustion, vehicles emissions, industrial process, and secondary aerosols were the main source categories for inland directions. In addition, potential HM and PAH risks from inland and marine directions were explored. The non-cancerous effects of TI were mainly affected by inland transport, especially from the southeast, northwest, and west-northwest. The cancerous effects of TI were mainly simultaneously affected by the inland direction and marine direction of transport.

Study on the Comprehensive Improvement of Ecosystem Services in a China’s Bay City for Spatial Optimization

Ecosystem services are characterized by region and scale, and contribute to human welfare. Taking Yantai city, a typical bay city in China, as the example, its three representative ecosystem services: food supply (FS), carbon sequestration (CS) and water yield (WY) were chosen as study targets. Based on analyzation of six different aspects of the supply and variation characteristic of demand, this study tried to propose advices for comprehensive improvement of ecosystem services for spatial optimization. The results showed that: (1) ecosystem services supply was strong in central and southern areas of Yantai, while the northern coastal areas were relatively weak; (2) synergistic relationships were found of FS-CS, FS-WY and CS-WY both in 2009 and 2015, with the strongest one for FS-WY. Additionally, in the synergistic relationships, each pair of ecosystem services was dominated by one ecosystem service; (3) most of the three pairs of synergistic relationships had the tendency to strengthen with larger scales; (4) four ecosystem demands changing areas were observed and comprehensive improvement suggestions for them were proposed. This work provides a new attempt to improve ecosystem services based on its supply-demand relationship, which will give a baseline reference for related studies in Yantai city, as well as other similar bay cities.

The Research Progress of the Influence of Agricultural Activities on Atmospheric Environment in Recent Ten Years: A Review

In recent years, the industrial emission of air pollution has been reduced via a series of measures. However, with the rapid development of modern agriculture, air pollution caused by agricultural activities is becoming more and more serious. Agricultural activities can generate a large amount of air pollutants, such as ammonia, methane, nitrogen oxides, volatile organic compounds, and persistent organic pollutants, the sources of which mainly include farmland fertilization, livestock breeding, pesticide use, agricultural residue burning, agricultural machinery, and agricultural irrigation. Greenhouse gases emitted by agricultural activities can affect regional climate change, while atmospheric particulates and persistent organic pollutants can even seriously harm the health of surrounding residents. With the increasing threat of agricultural air pollution, more and more relevant studies have been carried out, as well as some recommendations for reducing emissions. The emissions of ammonia and greenhouse gases can be significantly reduced by adopting reasonable fertilization methods, scientific soil management, and advanced manure treatment systems. Regarding pesticide use and agricultural residues burning, emission reduction are more dependent on the restriction and support of government regulations, such as banning certain pesticides, prohibiting open burning of straw, and supporting the recycling and reuse of residues. This review, summarizing the relevant research in the past decade, discusses the current situation, health effects, and emission reduction measures of agricultural air pollutants from different sources, in order to provide some help for follow-up research.

Dual-modelling-based source apportionment of NOx in five Chinese megacities: Providing the isotopic footprint from 2013 to 2014

In China, nitrate (NO₃^-) becomes the main contributor to fine particles (PM_2.5) because the emissions of its precursor, nitrogen oxides (NO_x), were not recognized and controlled well in recent years. In this work, sources, conversion, and geographical origin of NO_x were interpreted combining the isotopic information (δ¹⁵N and δ¹⁸O) of NO₃^- and dual modelling at five Chinese megacities (Beijing, Shanghai, Guangzhou, Wuhan and Chengdu) during 2013-2014. Results showed that the δ¹⁵N-NO₃^- values (n = 512) ranged from -12.3‰ to +22.9‰, and the average δ¹⁸O-NO₃^- value was +83.4‰ ± 17.2‰. The isotopic compositions both had a rising tendency as ambient temperature dropped, attributing largely to the source changes. Bayesian model indicated the percentage for the OH pathway of NO_x conversion had a clear seasonal variation with a higher value during summer (58.0% ± 9.82%) and a lower value during winter (11.1% ± 3.99%); it was also significantly correlated with latitude (p < 0.01). Coal combustion was the most important source of NO_x (31.1%-41.0%), which was geographically derived from North China and other south-central developed regions implied by Potential Source Contribution Function (PSCF). Apart from Chengdu, mobile sources was the second largest contributor to NO_x. This source was extensive but uniformly distributed all around the typical urban agglomerations of China. Biomass burning and microbial processes shared similar source areas, mostly originating from the North China Plain and Sichuan Basin. Based on the NO_x features, we infer that residential coal combustion was the primary source of heavy PM_2.5 pollution in Chinese megacities. Controlling the source categories of these regional priorities would help mitigate atmospheric pollution in these areas.

Nitrous acid in marine boundary layer over eastern Bohai Sea, China: Characteristics, sources, and implications

Nitrous acid (HONO) serves as a key source of hydroxyl radicals and plays important roles in atmospheric photochemistry. In this study, gaseous HONO and related species and parameters were measured in autumn of 2016 at a marine background site on Tuoji Island in eastern Bohai Sea, China. The HONO concentration in marine boundary layer (MBL) was on average 0.20 ± 0.20 ppbv (average ± standard deviation) with a maximum hourly value of 1.38 ppbv. It exhibited distinct diurnal variations featuring with elevated concentrations in the late night and frequent concentration peaks in the early afternoon. During nighttime, the HONO was produced at a fast rate with the NO₂-HONO conversion rate ranging from 0.006 to 0.036 h^-1. The fast HONO production and the strong dependence of temperature implied the enhancement of nocturnal HONO formation caused by air-sea interactions at high temperature. At daytime, HONO concentration peaks were frequently observed between 13:00-15:00. The observed daytime HONO concentrations were substantially higher than those predicted in the photostationary state in conditions of intensive solar radiation and high temperature. Strong or good correlations between the missing HONO production rate and temperature or photolysis frequency suggest a potential source of HONO from the photochemical conversions of nitrogen-containing compounds in sea microlayer. The source intensity strengthened quickly when the temperature was high. The abnormally high concentrations of daytime HONO contributed a considerable fraction to the primary OH radicals in the MBL.

Enhanced and selective adsorption of Hg2+ to a trace level using trithiocyanuric acid-functionalized corn bract

A novel trithiocyanuric acid-modified corn bract (TCA-CCB) was prepared, and its removal properties for Hg²⁺ were investigated. TCA-CCB showed a remarkable absorbability for Hg²⁺ in mixed ion solutions. Adsorption kinetics experiments indicated that the removal of Hg²⁺ on TCA-CCB was quick, with a removal rate of 99.07% within 5 min. In addition, the removal rate of Hg²⁺ exceeded 98% over all pH conditions. The adsorption process can be best described by pseudo-second-order kinetic and Hill isotherm models. The saturated adsorption capacity of TCA-CCB for Hg²⁺ was 390 mg/g. The TCA-CCB could efficiently adsorb Hg²⁺ from the simulated wastewater and reduce the Hg²⁺ concentration from 10 ppm to 12.35 ppb, which was lower than the greatest allowable value of 50 ppb and satisfied the emission standards required by the Chinese government. Moreover, the removal rate of Hg²⁺ was beyond 99% after three cycles. The results of the zeta potential and X-ray photoelectron spectroscopy (XPS) implied that the chelation and ion exchange between amino/thiol groups and Hg²⁺ played a significant role in the improvement of the adsorption properties. The corn bract modified by trithiocyanuric acid exhibits apparent advantages in the removal of Hg²⁺ from ppm to ppb due to its high selectivity, adsorption capacity and stability.

Assessment and quantification of NOx sources at a regional background site in North China: Comparative results from a Bayesian isotopic mixing model and a positive matrix factorization model

Regional sources of nitrogen oxides (NO_x) in North China during summer were explored using both a Bayesian isotopic mixing model and a positive matrix factorization (PMF) model. Results showed that the nitrogen isotope (δ¹⁵N) composition of particulate nitrate (NO₃^-) varied between -8.9‰ and +14.1‰, while the oxygen isotope (δ¹⁸O) composition ranged from +57.4‰ to +93.8‰. Based on results from the Bayesian isotopic mixing model, the contribution of the hydroxyl radical (•OH) NO_x conversion pathway showed clear diurnal fluctuation; values were higher during the day (0.53 ± 0.16) and lower overnight (0.42 ± 0.17). Values peaked at 06:00-12:00 and then decreased gradually until 00:00-06:00 the next day. Coal combustion (31.34 ± 9.04%) was the most significant source of NO_x followed by biomass burning (25.74 ± 2.58%), mobile sources (23.83 ± 3.66%), and microbial processes (19.09 ± 5.21%). PMF results indicated that the contribution from mobile sources was 19.83%, slightly lower as compared to the Bayesian model (23.83%). The PMF model also reported a lower contribution from coal combustion (28.65%) as compared to the Bayesian model (31.34%); however, the sum of biomass burning and microbial processes in the Bayesian model (44.83%) was lower than the aggregate of secondary inorganic aerosol, sea salt, and soil dust in PMF model (51.52%). Overall, differences between the two models were minor, suggesting that this study provided a reasonable source quantification for NO_x in North China during summer.

Oxidative potential of ambient PM2.5 in the coastal cities of the Bohai Sea, northern China: Seasonal variation and source apportionment

Emissions of air pollutants from primary and secondary sources in China are considerably higher than those in developed countries, and exposure to air pollution is main risk of public health. Identifying specific particulate matter (PM) compositions and sources are essential for policy makers to propose effective control measures for pollutant emissions. Ambient PM_2.5 samples covered a whole year were collected from three coastal cities of the Bohai Sea. Oxidative potential (OP) was selected as the indicator to characterize associated PM compositions and sources most responsible for adverse impacts on human health. Positive matrix factorization (PMF) and multiple linear regression (MLR) were employed to estimate correlations of PM_2.5 sources with OP. The volume- and mass-based dithiothreitol (DTT_v and DTT_m) activities of PM_2.5 were significantly higher in local winter or autumn (p < 0.01). Spatial and seasonal variations in DTT_v and DTT_m were much larger than mass concentrations of PM_2.5, indicated specific chemical components are responsible for PM_2.5 derived OP. Strong correlations (r > 0.700, p < 0.01) were found between DTT activity and water-soluble organic carbon (WSOC) and some transition metals. Using PMF, source fractions of PM_2.5 were resolved as secondary source, traffic source, biomass burning, sea spray and urban dust, industry, coal combustion, and mineral dust. Further quantified by MLR, coal combustion, biomass burning, secondary sources, industry, and traffic source were dominant contributors to the water-soluble DTT_v activity. Our results also suggested large differences in seasonal contributions of different sources to DTT_v variability. A higher contribution of DTT_v was derived from coal combustion during the local heating period. Secondary sources exhibited a greater fraction of DTT_v in summer, when there was stronger solar radiation. Traffic sources exhibited a prevailing contribution in summer, and industry contributed larger proportions in spring and winter. Future abatement priority of air pollution should reduce the sources contributing to OP of PM_2.5.

Assessing on toxic potency of PM2.5-bound polycyclic aromatic hydrocarbons at a national atmospheric background site in North China

A total of 76PM_2.5 samples collected at Tuoji Island from November 2011 to January 2013 were used to analyze 15 congeners of polycyclic aromatic hydrocarbons (∑₁₅PAHs) and assess their toxic potency. The average ∑₁₅PAHs was 15.34±8.87ngm^-3, ranging from 4.24 to 40.62ngm^-3 over the sampling period. BkF, BbF, Phe and BaP were dominant PAH congeners, contributing together 60.64% of the ∑₁₅PAH concentration. The highest monthly ∑₁₅PAHs concentration was in January 2012, followed by the next January, which was closely four times greater than the lowest level occurred in July 2012. Wheat straw burning was responsible for the high PAH concentrations in June 2012. The averaged BaP toxicity equivalent (TEQ-BaP) concentration was 2.70±1.88ngm^-3 over the sampling period. BaP and DaA were the largest contributors, which contributed 58.5% and 14.7% of totals, respectively. The high TEQ-BaP and TEQ-BaP value per unit of ∑₁₅PAHs concentration (TEQ-BaP(U)) values occurred in the cold season and the low levels presented in the warm period. The heaviest monthly TEQ-BaP was 5.28±2.84ngm^-3, which appeared in January 2012; the lowest value was 0.86±0.33ngm^-3, which occurred in July 2012. The potential source contribution function (PSCF) showed the occurrence of the high health risk associated with PAHs in the middle of Liaoning and the south of Shandong Peninsula.

Combining Positive Matrix Factorization and Radiocarbon Measurements for Source Apportionment of PM2.5 from a National Background Site in North China

To explore the utility of combining positive matrix factorization (PMF) with radiocarbon (¹⁴C) measurements for source apportionment, we applied PM_2.5 data collected for 14 months at a national background station in North China to PMF models. The solutions were compared to ¹⁴C results of four seasonally averaged samples and three outlier samples. Comparing the most readily interpretable PMF solutions and ¹⁴C results revealed that PMF modeling was well able to capture the source patterns of PM_2.5 with two and three irrelevant source classifications for the seasonal and outlier samples. The contribution of sources that could not be classified as either fossil or non-fossil sources in the PMF solution, and the errors between the modeled and measured concentrations weakened the effectiveness of the comparison. Based on these two factors, we developed an index for selecting the most suitable ¹⁴C measurement samples for combining with the PMF model. Then we examined the potential for coupling PMF modeling and ¹⁴C data with a constrained PMF run using the ¹⁴C data as a priori information. The restricted run could provide a more reliable solution; however, the PMF model must provide a flexible dialog to input the priori restrictions for executing the constraint simulation.

Polyethylenimine-Functionalized Corn Bract, an Agricultural Waste Material, for Efficient Removal and Recovery of Cr(VI) from Aqueous Solution

In this study, polyethylenimine-functionalized corn bract (PEI-CB) was first used to remove aqueous Cr(VI) via the "waste control by waste" concept. The results indicated that PEI-CB had an excellent performance for Cr(VI) removal and the maximum removal capacity was 438 mg/g. The adsorption of Cr(VI) was fitted to the Langmuir model, and kinetics of uptake could be described by a pseudo-second-order rate model well. Amine was proven to be the active center for Cr(VI) adsorption and partial reduction to Cr(III), while removal efficiency was enhanced at a lower pH value and higher temperature. Besides, nanosized Cr₂O₃ with a high purity was obtained by simple calcination of a Cr(VI)-laden adsorbent. Hence, this study provided a novel strategy for Cr(VI) wastewater remediation and pure Cr₂O₃ recovery. Prepared PEI-CB was then a promising alternative of low cost for replacement of the current expensive absorbent of removing Cr(VI) from wastewater from the view of sustainability.

Source apportionment of sediment organic material in a semi-enclosed sea using Bayesian isotopic mixing model

To determine sources of organic material in semi-enclosed Bohai Sea, samples of marine surface sediments, suspended particulates in adjacent rivers and atmospheric deposition were collected and analyzed for grain size composition, total organic carbon(TOC and POC), total nitrogen (TN and PN), and stable isotopic composition (δ¹³C and δ¹⁵N). Measured bulk C/N ratio (5.50-12.28), δ¹³C (-23.59~-19.54‰), and δ¹⁵N (2.80-8.07‰) values of surface sediment organic materials indicated a mixed source of marine and terrestrial contributions. Spatial distribution of organic C, N and their stable isotope composition indicated a land-sea gradient of organic material content and source combination. Using MixMIR model with dual isotopes, it was estimated that relative contributions of marine, riverine, and atmospheric sources to sediment mixture were 69.0%, 9.6%, and 21.4%, respectively. Our results demonstrated the advantage of Bayesian isotope mixing models over the conventional end-member mixing models for source apportionment in coastal seas with complex source origins.

First Assessment of NOx Sources at a Regional Background Site in North China Using Isotopic Analysis Linked with Modeling

Nitrogen oxides (NO_x, including NO and NO₂) play an important role in the formation of atmospheric particles. Thus, NO_x emission reduction is critical for improving air quality, especially in severely air-polluted regions (e.g., North China). In this study, the source of NO_x was investigated by the isotopic composition (δ¹⁵N) of particulate nitrate (p-NO₃^-) at Beihuangcheng Island (BH), a regional background site in North China. It was found that the δ¹⁵N-NO₃^- (n = 120) values varied between -1.7‰ and +24.0‰ and the δ¹⁸O-NO₃^- values ranged from 49.4‰ to 103.9‰. On the basis of the Bayesian mixing model, 27.78 ± 8.89%, 36.53 ± 6.66%, 22.01 ± 6.92%, and 13.68 ± 3.16% of annual NO_x could be attributed to biomass burning, coal combustion, mobile sources, and biogenic soil emissions, respectively. Seasonally, the four sources were similar in spring and fall. Biogenic soil emissions were augmented in summer in association with the hot and rainy weather. Coal combustion increased significantly in winter with other sources showing an obvious decline. This study confirmed that isotope-modeling by δ¹⁵N-NO₃^- is a promising tool for partitioning NO_x sources and provides guidance to policymakers with regard to options for NO_x reduction in North China.

Chemical characteristics and influence of continental outflow on PM1.0, PM2.5 and PM10 measured at Tuoji island in the Bohai Sea

To investigate the chemical characteristics and sources of size-segregated particles in the background region, PM_1.0, PM_2.5 and PM₁₀ samples were collected in Tuoji Island (TI) during the winter of 2014. Water-soluble inorganic ions (WSIIs) including Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺, Cl^-, NO₃^- and SO₄^2-, organic carbon (OC) and elemental carbon (EC) and water-soluble organic carbon (WSOC) were analysed. The average mass concentrations of PM_1.0, PM_2.5 and PM₁₀ were 44.5μg/m³, 62.0μg/m³ and 94.4μg/m³, respectively, and particles were importantly enriched in PM_1.0. Secondary WSIIs (NH₄⁺, NO₃^- and SO₄^2-) were the most abundant species, and their contribution was highest in PM_1.0. The average values of NOR and SOR were more than 0.1 in PM_1.0, suggesting that secondary formation of SO₄^2- and NO₃^- from the gas precursors SO₂ and NO₂ occurred in PM_1.0. Secondary organic carbon accounted for 62.3% in PM_1.0, 61.9% in PM_1.0-2.5 and 48.9% in PM_2.5-10 of OC, formed mainly in the fine mode. The particles concentrations were mainly affected by air mass from the North China Plain, especially the air mass from the southwest of Shandong province, which had low speed and altitude.

Radiocarbon-based impact assessment of open biomass burning on regional carbonaceous aerosols in North China

Samples of total suspended particulates (TSPs) and fine particulate matter (PM2.5) were collected from 29th May to 1st July, 2013 at a regional background site in Bohai Rim, North China. Mass concentrations of particulate matter and carbonaceous species showed a total of 50% and 97% of the measured TSP and PM2.5 levels exceeded the first grade national standard of China, respectively. Daily concentrations of organic carbon (OC) and elemental carbon (EC) were detected 7.3 and 2.5 μg m(-3) in TSP and 5.2 and 2.0 μg m(-3) in PM2.5, which accounted 5.8% and 2.0% of TSP while 5.6% and 2.2% for PM2.5, respectively. The concentrations of OC, EC, TSP and PM2.5 were observed higher in the day time than those in the night time. The observations were associated with the emission variations from anthropogenic activities. Two merged samples representing from south and north source areas were selected for radiocarbon analysis. The radiocarbon measurements showed 74% of water-insoluble OC (WINSOC) and 59% of EC in PM2.5 derived from biomass burning and biogenic sources when the air masses were from south region, and 63% and 48% for the air masses from north, respectively. Combined with backward trajectories and daily burned area, open burning of agricultural wastes was found to be predominating, which was confirmed by the potential source contribution function (PSCF).