Shangdianzi Research Articles

A quality-assured dataset of nine radiation components observed at the Shangdianzi regional GAW station in China (2013–2022)

Abstract. The New Baseline Surface Radiation (NBSR) system was established at the Shangdianzi (SDZ) regional Global Atmosphere Watch (GAW) station in 2013 to observe nine broadband radiation components, i.e. the global, direct, diffuse, and upwelling shortwave irradiance (GSWI, DSWI, DifSWI, and UpSWI); the photosynthetically active radiation (PAR); the ultraviolet irradiance (UVAI and UVBI); and the down- and upwelling longwave irradiance (DnLWI and UpLWI). To test the 1 min raw radiometric data, a Hybrid Algorithm for Radiation Data Quality Control (HARDQC) is presented in this study based on well-established methods, together with the solar irradiance dataset and the spectral features of the instrument bands. Subsequently, a NBSR dataset, which consists of radiation data at multiple timescales (i.e. 1 min, hourly, daily, monthly, monthly average hourly, and monthly average daily) over 2013–2022, is established and evaluated. Results show that more than 98.7 % of all radiation components passed the physical possibility test. The percentages of those that passed the extremely rare test are greater than 98.6 % for all radiation components except for the DnLWI (97.1 %). The percentages of those that passed the comparison test are greater than 83.3 % (GSWI), 78.3 % (DSWI), 81.7 % (DifSWI), 93.1 % (UpSWI), 88.9 % (PAR), 95.6 % (UVAI), 96.3 % (UVBI), 99.8 % (DnLWI), and 99.7 % (UpLWI), respectively. Due to data logger faults, removal of the instruments for calibration, and lightning strikes, some apparent data gaps in the upwelling radiation components (January 2015–August 2017) and all radiation components (December 2018; July to September 2021) were detected. Despite the existence of a few imperfections in the NBSR dataset, it is still reliable to apply it in many fields such as the validation of satellite products and numerical models, the investigation of relationships between radiation and atmospheric composition, and the detection of changes in the surface fluxes. The dataset described in this paper is available at https://doi.org/10.1594/PANGAEA.963330 (Quan et al., 2023b).

On the Large Variation in Atmospheric CO2 Concentration at Shangdianzi GAW Station during Two Dust Storm Events in March 2021

Dust storms have large impacts on air quality and meteorological elements; however, their relationships with atmospheric greenhouse gases (e.g., CO2) and radiation components remain uncertain. In this study, the co-variation of dust and CO2 concentrations and its possible influencing mechanism are examined using observations at the Shangdianzi (SDZ) regional Global Atmosphere Watch (GAW) station along with simulations of the Vegetation Photosynthesis and Respiration Model coupled with the Weather Research and Forecasting model (WRF-VPRM), during two dust storm events on 15 and 28 March 2021. During these events, hourly CO2 concentrations decreased by 40–50 ppm at SDZ while dust concentrations increased to 1240.6 and 712.4 µg m−3. The elevated dust increased diffusive shortwave irradiance by 50–60% and decreased direct shortwave irradiance by ~60% along with clouds. The dust events were attributed to the passages of two cold front systems over northern China. At SDZ, during the frontal passages, wind speed increased by 3–6 m s−1, and relative humidity decreased by 50–60%. The CO2 variations associated with the frontal systems were captured by the WRF-VPRM despite the overestimated surface CO2 level at SDZ. Biogenic CO2 flux plays an indistinctive role in the large CO2 variation at SDZ, as it is weak during the non-growing season. The cold fronts pushed polluted air southeastward over the North China Plain and replaced it with low-CO2 air from Northwest China, leading to the decline in CO2. These findings demonstrate that mesoscale synoptic conditions significantly affect the regional transport and dispersion of CO2, which can influence the prediction of terrestrial carbon balance on a regional scale.

In Situ Observations of Halogenated Gases at the Shangdianzi Background Station and Emission Estimates for Northern China.

Halogenated gases include ozone-depleting substances and greenhouse gases, such as chlorofluorocarbons, halons, hydrochlorofluorocarbons, hydrofluorocarbons, and perfluorinated gases. In situ atmospheric observations of major halogenated gases were conducted at the Shangdianzi (SDZ) background station, China, from October 2020 to September 2021 using ODS5-pro, a newly developed measurement system. The measurement time series of 36 halogenated gases showed occasional pollution events, where background conditions represented 25% (CH2Cl2) to 81% (CF3Cl, CFC-13) of the measurements. The annual mean background mole fractions of most species at SDZ were consistent with those obtained at the Mace Head station in Ireland. The background conditions were distinguished from pollution events, and the enhanced mole fractions were used to estimate the emissions of four categories of fluorinated gases (F-gases) from northern China using a tracer ratio method. The CO2-equivalent (CO2-equiv) emission of F-gases from northern China reached 181 ± 18 Tg year-1 during 2020-2021. Among the four categories of F-gases estimated, SF6 accounted for the highest proportion of CO2-equiv emissions (24%), followed by HFC-23 (22%), HFC-125 (17%), HFC-134a (13%), NF3 (10%), CF4 (5.9%), HFC-143a (3.9%), HFC-32 (3.4%), and HFC-152a (0.2%).

Measurement report: Variations in surface SO<sub>2</sub> and NO<sub><i>x</i></sub> mixing ratios from 2004 to 2016 at a background site in the North China Plain

Abstract. Strict air pollution control strategies have been implemented in recent decades in the North China Plain (NCP), previously one of the most polluted regions in the world, and have resulted in considerable changes in emissions of air pollutants. However, little is so far known about the long-term trends of the regional background level of NOx and SO2, along with the increase and decrease processes of regional emissions. In this study, the seasonal and diurnal variations of NOx and SO2 as well as their long-term trends at a regional background station in the NCP were characterized from 2004 to 2016. On average, SO2 and NOx mixing ratios were 5.7 ± 8.4 and 14.2 ± 12.4 ppb, respectively. The seasonal variations in SO2 and NOx mixing ratios showed a similar pattern, with a peak in winter and a valley in summer. However, the diurnal variations in SO2 and NOx mixing ratios greatly differed for all seasons, indicating different sources for SO2 and NOx and meteorological effects on their concentrations. Overall, the annual mean SO2 exhibited a significant decreasing trend of −6.1 % yr−1 (R = −0.84, P < 0.01) from 2004 to 2016, which is very close to −6.3 % yr−1 of the annual SO2 emission in Beijing, and a greater decreasing trend of −7.4 % yr−1 (R = −0.95, P < 0.01) from 2008 to 2016. The annual mean of NOx showed a fluctuating rise of +3.4 % yr−1 (R = 0.38, P = 0.40) from 2005 to 2010, reaching the peak value (16.9 ppb) in 2010, and then exhibited an extremely significant fluctuating downward trend of −4.5 % yr−1 (R = 0.95, P < 0.01) from 2010 to 2016. After 2010, the annual mean NOx mixing ratios correlated significantly (R = 0.94, P < 0.01) with the annual NOx emission in North China. The decreasing rate (−4.8 % yr−1, R = −0.92, P < 0.01) of the annual mean NOx mixing ratios from 2011 to 2016 at the Shangdianzi (SDZ) regional atmospheric background station is lower than the one (−8.8 % yr−1, R = −0.94, P < 0.01) for the annual NOx emission in the NCP and in Beijing (−9.0 % yr−1, R = −0.96, P < 0.01). This indicated that surface NOx mixing ratios at SDZ had a weaker influence than SO2 on the emission reduction in Beijing and its surrounding areas in the NCP. The increase in the number of motor vehicles led to an increase in traffic emissions for NOx. This study supported conclusions from previous studies that the measures taken for controlling NOx and SO2 in the NCP in the past decades were generally successful. However, NOx emission control should be strengthened in the future.

Chemical characteristics and source apportionments of volatile organic compounds (VOCs) before and during the heating season at a regional background site in the North China Plain

We investigated the characteristics and sources of volatile organic compounds (VOCs) at a regional background station on the North China Plain from 12 October to 31 December 2017. This study is unique in that emission sources of VOCs and their influence on ozone formation were identified for the first time at a regional background site in North China. The average total mixing ratio of VOCs was 16.0 ± 10.0 ppbv before the heating period (NHP, 12 October to 14 November), and this value was 43% higher than that during the heating period (HP, November 15 to 31 December). Alkanes were the dominant contributors to total VOCs and ranged from 59.9% to 67.1% during the HP and NHP. Relative humidity (RH) and temperature (T) dependence were observed before the HP, and high VOC mixing ratios were observed at relatively low T (−4 °C to 5 °C) and high RH (>60%) conditions and medium T (5 °C < T < 14 °C) and low RH (< 60%) conditions. High mixing ratios of VOCs were observed under RH > 55% and T < −1 °C conditions during the HP. Through bivariate polar plots, medium or low mixing ratios of total VOCs (TVOCs) were found at low wind speeds (<2 m s−1) before the HP, whereas a high mixing ratio was found during the HP, highlighting the important role of local source emissions during the HP. In addition, southwest winds at high wind speeds (>4 m s−1) were essential for the regional transport of pollutants. The contributions of alkenes to LOH (OH radical loss rate) and OFP (ozone formation potential) before and during the HP were as high as 48.8%–62.9% and 49.7% -64.4%, respectively. The OFP and LOH of ethene presented higher levels before and during the HP, elucidating the significant role of alkenes in the formation of O3 at SDZ site. Four emission sources of VOCs, including coal burning, liquefied petroleum gas (LPG) and natural gas (NG) usage, vehicular emissions and gasoline evaporation, were resolved using a positive matrix factorization (PMF) model, with contributions of 45.4%, 15.8%, 23.4% and 15.4%, respectively. The concentration weighted trajectory (CWT) analysis indicated that the main potential source regions were located to the south and southwest of Shangdianzi (SDZ) before the HP, and they were characterized by a narrow pollution band along Hengshui-Baoding-Langfang-Beijing. High CWT values were primarily distributed in a small region in southern SDZ during the HP, emphasizing the role of local emissions and transport from surrounding regions, especially urban areas of Beijing.

Tree-ring Δ14C time series from 1948 to 2018 at a regional background site, China: Influences of atmospheric nuclear weapons tests and fossil fuel emissions

Δ14C values were measured from tree-rings (1948–2018) of Pinus tabuliformis Carr. that grew at the Shangdianzi (SDZ) regional background site in China. The objectives of this study are to establish a record of atmospheric Δ14C, and to evaluate the influences of Chinese atmospheric nuclear tests and fossil carbon emissions on atmospheric Δ14C variations. The SDZ tree-ring Δ14C values are negative before 1956, and increase dramatically in response to global atmospheric nuclear tests, with a peak value of 844.0 ± 4.2‰ in 1964. After the Partial Test Ban Treaty in 1963, the Δ14C values at SDZ decrease exponentially during 1964–2018. The half-life of the Δ14C decrease was protracted by approximately 2.7 yr during 1964–1984, due to Chinese atmospheric nuclear tests as well as Chinese forests as a carbon source during that period. Massive fossil carbon emissions in China lead to the SDZ decrease rate that is about 1.8‰ yr−1 faster than that for the Northern Hemisphere background region during 2000–2010. SDZ Δ14C since 2000 show strong negative correlations with fossil carbon emissions from the Beijing-Tianjin-Hebei (BTH) region (r2 = 0.954) and China (r2 = 0.950), and a 1‰ decrease in SDZ Δ14C indicates an increase of 2.3 ± 0.2 Mt C and 23.3 ± 1.7 Mt C fossil carbon emissions from the BTH region and China, respectively.

Real-time measurements of aromatic hydrocarbons at a regional background station in North China: Seasonal variations, meteorological effects, and source implications

We performed long-term, real-time measurements of BTEX species using the on-line Syntech Spectras GC955 analyzers at a regional background site in the North China Plain (Shangdianzi site), from December 2017 to November 2018. This study is unique in that it is the first long-term measurement of BTEX species in a regional background site in north China. The seasonal averaged mixing ratio of total BTEX ranged from 0.47 ppbv in the summer to 1.44 ppbv in the spring, with the contribution of benzene being the highest at 49–61%, followed by toluene at 25–31%. The maximal values of BTEX in spring were strongly associated with the regional transport under the influence of prevailing southwesterly winds and high WS. The effects of RH and T on the BTEX mixing ratio and composition variations were varied in different seasons. High mixing ratios of BTEX were observed under relatively low T (−15 °C < T < 3 °C) and relatively high RH (60% < RH < 85%) conditions in winter and fall. While significantly low mixing ratios of BTEX were observed under high RH (>85%) and T (>12 °C) conditions during summer. Furthermore, the O3 concentration was generally high (~20–40 ppbv) under dry conditions (RH < 40%) and gradually increased to a high level (>50 ppbv) at high RH (>40%) and T (>12 °C). All BTEX species exhibited evident wind gradients, characterized by high concentrations correlated with winds from the southeast, south, and southwest directions. This was coincided with the results obtained from the concentration weighted trajectory (CWT) analysis, which indicated that the areas with a higher contribution to BTEX concentration were mainly distributed in the south and southwest of Shangdianzi (SDZ). It is worth noting that smaller source areas were found in winter compared with that in other three seasons, owing to the transportation of regional emissions. The significantly lower mean T/B ratios observed during the daytime and nighttime were 0.48 and 0.58, respectively, which implicated the impact of biomass burning at SDZ. The ratios of X/E during the daytime and nighttime were 0.82 and 1.07, respectively, which indicated a relatively more aged air mass at daytime.

Temporal patterns and source regions of atmospheric carbon monoxide at two background stations in China

Atmospheric carbon monoxide (CO) was continuously measured from 2010/2011 to 2017 at Lin'an (LAN) and Shangdianzi (SDZ) background station in the economically developed region in China using cavity ring-down spectrometers. Diurnal variations of CO mixing ratio displayed a bimodal in all seasons, with the peak to trough amplitudes larger than 43.6 ± 18.5 (95% CI) ppb at LAN and 80.5 ± 47.0 ppb at SDZ, reflecting the influence of anthropogenic emissions. Seasonal variation at LAN was in accordance with those observed in the northern hemisphere. Due to the multiple influences of regional sources and meteorological transport, CO at SDZ displayed an abnormal pattern, with a maximum in summer and the minimum in autumn. CO levels decreased at a rate of 16.3 ± 0.3 ppb yr−1 at LAN and 1.3 ± 0.4 ppb yr−1 at SDZ during the six-year period. The 3-day back trajectory by the HYSPLIT model showed that high CO at LAN was mainly from the economically developed regions, including the North China Plain, the Middle-Lower Yangtze Plain and the eastern region of the station. The analysis by concentration-weighted trajectory (CWT) approach indicated that large-scale of strong source regions were uniformly distributed around the LAN site in all seasons. At SDZ, atmospheric CO was severely influenced by monsoons and air masses from the south-southeastern site. Major source areas were identified in megacities such as Beijing, Tianjin, and Tangshan, especially in summer. Consequently, most of the atmospheric CO mole fractions at SDZ could be defined into two subsets, with higher values associated with air masses from the south and lower ones from the north.

Tropospheric NO2 vertical column densities retrieved from ground-based MAX-DOAS measurements at Shangdianzi regional atmospheric background station in China

Ground-basedMulti-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements were performed at Shangdianzi (SDZ) regional atmospheric background station in northern China from March 2009 to February 2011. The tropospheric NO2 vertical column densities (VCDs) were retrieved to investigate the background condition of the Beijing–Tianjin–Hebei developed economic circle in China. The seasonal variation of mean NO2 tropospheric VCDs (VCDTrop) at SDZ is apparent, with the maximum (1.3 × 1016 molec/cm2) in February and the minimum (3.5 × 1015 molec/cm2) in August, much lower than those observed at the Beijing city center. The average daytime diurnal variations of NO2 VCDTrop are rather consistent for all four seasons, presenting the minimum at noon and the higher values in the morning and evening. The largest and lowest amplitudes of NO2 VCDTrop diurnal variation appear in winter and in summer, respectively. The diurnal pattern at SDZ station is similar to those at other less polluted stations, but distinct from the ones at the urban or polluted stations. Tropospheric NO2 VCDs at SDZ are strongly dependent on the wind, with the higher values being associated with the pollution plumes from Beijing city. Tropospheric NO2 VCDs derived from ground-based MAX-DOAS at SDZ show to be well correlated with corresponding OMI (Ozone Monitoring Instrument) satellite products with a correlation coefficient R = 0.88. However, the OMI observations are on average higher than MAX-DOAS NO2 VCDs by a factor of 28%, probably due to the OMI grid cell partly covering the south of SDZ which is influenced more by the pollution plumes from the urban areas.

Potential source regions of air pollutants at a regional background station in Northern China

ABSTRACTUnderstanding the potential source regions of air pollutants and their relative contribution from surrounding areas are of great importance for air pollution control strategies in Northern China. Six years of measurement of air pollutants was conducted from 2005 to 2010 in Shangdianzi (SDZ) regional background station. During the study period, the annual average concentrations of sulfur dioxide (SO2), carbon monoxide (CO), nitrogen dioxide and ozone (Ox), and fine particle matter less than or equal to 2.5 μm (PM2.5) range from 15.7 to 20.0 μg/m3, 577.7 to 856.0 μg/m3, 90.4 to 101.8 μg/m3, and 39.8 to 62.4 μg/m3, respectively. In this work, Potential Source Contribution Function (PSCF) and Trajectory Sector Analysis (TSA) methods are applied to identify locations of sources and their relatively contribution of air pollutants at SDZ. PSCF analysis shows that central Inner Mongolia, north Shanxi, west and south Hebei, and west Liaoning are all potential sources of SO2. The North China Plain (NCP) region, especially south Hebei and north Shandong, are major potential source regions for CO, Ox, and PM2.5. Therefore, reducing anthropogenic emissions from the coal industry, biomass burning, agricultural activities, and vehicles in these areas could be an effective way of controlling air pollution at SDZ. Based on the TSA results, the contributions of SO2, CO, Ox, and PM2.5 from long-distance transport are 5.5 μg/m3, 301.4 μg/m3, 14.8 μg/m3, and 25.8 μg/m3, accounting for approximately 22.6%, 32.3%, 13.1%, and 37.5% of the respective air pollutant concentrations at SDZ.

Comparison of atmospheric CO2 mole fractions and source–sink characteristics at four WMO/GAW stations in China

As CO2 is a primary driving factor of climate change, the mole fraction and source–sink characteristics of atmospheric CO2 over China are constantly inferred from multi-source and multi-site data. In this paper, we compared ground-based CO2 measurements with satellite retrievals and investigated the source–sink regional representativeness at China's four WMO/GAW stations. The results indicate that, firstly, atmospheric CO2 mole fractions from ground-based sampling measurement and Greenhouse Gases Observing Satellite (GOSAT) products reveal similar seasonal variation. The seasonal amplitude of the column-averaged CO2 mole fractions is smaller than that of the ground-based CO2 at all stations. The extrema of the seasonal cycle of ground-based and column CO2 mole fractions are basically synchronous except a slight phase delay at Lin'an (LAN) station. For the two-year average, the column CO2 is lower than ground-based CO2, and both of them reveal the lowest CO2 mole fraction at Waliguan (WLG) station. The lowest (∼4 ppm) and largest (∼8 ppm) differences between the column and ground-based CO2 appear at WLG and Longfengshan (LFS) stations, respectively. The CO2 mole fraction and its difference between GOSAT and ground-based measurement are smaller in summer than in winter. The differences of summer column CO2 among these stations are also much smaller than their ground-based counterparts. In winter, the maximum of ground-based CO2 mole fractions and the greatest difference between the two (ground-based and column) datasets appear at the LFS station. Secondly, the representative areas of the monthly CO2 background mole fractions at each station were found by employing footprints and emissions. Smaller representative areas appeared at Shangdianzi (SDZ) and LFS, whereas larger ones were seen at WLG and LAN. The representative areas in summer are larger than those in winter at WLG and SDZ, but the situation is opposite at LAN and LFS. The representative areas for the stations are different in summer and winter, distributed in four typical regions. The CO2 net fluxes in these representative areas show obvious seasonal cycles with similar trends but different varying ranges and different time of the strongest sink. The intensities and uncertainties of the CO2 fluxes are different at different stations in different months and source-sink sectors. Overall, the WLG station is almost a carbon sink, but the other three stations present stronger carbon sources for most of the year. These findings could be conducive to the application of multi-source CO2 data and the understanding of regional CO2 source–sink characteristics and patterns over China.

Analysis of patterns in the concentrations of atmospheric greenhouse gases measured in two typical urban clusters in China

China is the largest emitter of greenhouse gases, and urban clusters play an essential role in China's carbon emissions because of the country's unbalanced economic development. In this paper, the discrete air sample measurements of atmospheric CO2, CH4, and CO during the period between 2007 and 2013 from Shangdianzi (SDZ) station in Jing-Jin-Ji (JJJ) region and Linan (LAN) station in Yangtze River Delta (YRD) region, respectively, are presented and characterized. By backward trajectory cluster analysis, the low background CO2 mole fraction and similar long-term trends with Waliguan global station (WLG) were observed at SDZ because most of the air masses originate mostly from remote clean terrestrial areas in the north with limited information of anthropogenic emissions. But the background CH4 and CO are influenced mainly by ruminants and rice field emission from the surrounding regions and urban cluster emission in the JJJ region, which lead to the higher CH4 and CO in summer at SDZ. Whereas, the CO2, CH4 and CO background values observed at LAN are higher by the combined effects of long-distance atmospheric transportation from Northern and Central China and urban clusters emission from the YRD region. The observed polluted data at SDZ and LAN are all strongly affected by regional and local anthropogenic emissions, which lead to the higher GHGs concentrations compared to the background data. However, because the air mass transportation from the north is weak in winter and no winter heating is required and vegetation photosynthesis is still stronger in the south of China, the CO2 concentration at LAN is lower than that at SDZ in autumn and winter. The polluted CO value at SDZ is found considerably higher than that at LAN, especially in spring and winter. By analyzing the correlations of observed regional enhanced values of CO2, CH4 and CO at the two stations, we find the significant correlation between them, which means they may share the common-source of anthropogenic emissions from the regional fossil fuel and biomass burning in cold season. Moreover, the high coal-consumption proportion with the low CO2 emissions factors, and much biomass burning with low combustion efficiency in JJJ region lead to the higher slope values of △CO2 and △CO in spring and winter at SDZ and considerably higher than that at LAN. The results can provide a further understanding of regional/local features of atmospheric GHGs under the influence of human activities in the urban clusters in China.

Sources and Characteristics of Regional Background PM1 in North China During the Autumn and Winter Polluted Period

The campaign of investigating the chemical compositions and particle size distributions of NR-PM1(non-refractory PM1) was conducted by using a High Resolution Time of Flight Aerosol Mass Spectrometer(HR-ToF-AMS) at the Shangdianzi(SDZ) regional atmospheric background site(117.07°E, 40.39°N), northeast of Beijing, from October 17th 2015 to January 27th 2016. The results showed that organics was the main component of PM1, and the proportion of nitrate was higher than that of sulfate in autumn and winter. The mean mass-resolved size distributions for the main components displayed accumulation mode. The wider organic peak shape and larger nitrate peak size indicated that the organics contributed to both small and large particles at the beginning of the particle formation, growth and aging processes, while most of nitrate particles preferred to grow into large particles during the aging process. The ratios of elements between OM and OC, O/C and H/C were calculated as 1.91, 0.58 and 1.58 respectively. The slope of Van Krevelen diagram of organic aerosols during polluted episode was -0.21, whose oxidation state was higher than those of other city sites. Nitrate was the major contributor of NR-PM1 during the polluted period, while organics was significantly higher than that during clean period. The results of back trajectories analysis demonstrated that the air masses were complex during the pollution episode. The northwest wind from central Inner Mongolia and Siberia dominated the clean episodes, which was conducive to the spread of pollutants.

Predicting PM2.5 Concentrations at a Regional Background Station Using Second Order Self-Organizing Fuzzy Neural Network

This study aims to develop a second order self-organizing fuzzy neural network (SOFNN) to predict the hourly concentrations of fine particulate matter (PM2.5) for the next 24 h at a regional background station called Shangdianzi (SDZ) in China from 14 to 23 January 2010. The structure of the SOFNN was automatically adjusted according to the sensitivity analysis (SA) of model output and the parameter-learning phase was performed applying a second order gradient (SOG) algorithm. Principal component analysis (PCA) was employed to select the dominating factors for PM2.5 concentrations as the input variables for the SOFNN. It was found that the dominating variables (relative humidity (RH), pressure (Pre), aerosol optical depth (AOD), wind speed (WS) and wind direction (WD)) extracted by PCA agreed well with the characteristics of PM2.5 at SDZ where the PM2.5 concentrations were heavily affected by meteorological parameters and were closely related to AOD. The forecasting results showed that the proposed SOG-SASOFNN performed better than other models with higher coefficient of determination (R2) during both training phase and test phase (0.89 and 0.84, respectively) in predicting PM2.5 concentrations at SDZ. In conclusion, the developed SOG-SASOFNN provided satisfying results for modeling the hourly distribution of PM2.5 at SDZ during the studied period.

Long-term trend of chemical composition of atmospheric precipitation at a regional background station in Northern China.

Understanding the trend of chemical composition of precipitation is of great importance for air pollution control strategies in Northern China. A comprehensive study on the long-term chemical compositions of precipitation was carried out from 2003 to 2014 at the Shangdianzi (SDZ) regional background station in northern China. All samples were analyzed for pH, electrical conductivity and major ions (F-, Cl-, NO3-, SO42-, NH4+, Mg2+, Ca2+, K+ and Na+). The average pH during this period was 4.53±0.35, which is considerably lower than those reported in other background stations in China (Linan, Waliguan and Longfengshan). NH4+, SO42-, Ca2+ and NO3- were the dominant ions in precipitation, with concentrations (volume-weighted mean) of 212.99μeqL-1, 200.20μeqL-1, 116.88μeqL-1 and 98.56μeqL-1, respectively. The ion concentrations at SDZ were much higher than those of other background stations and megacities in China. A significantly increasing trend was observed for NO3- (7.26%year-1), and a decreasing trend was observed for SO42-/NO3-, suggesting that the precipitation of SDZ evolved from a sulfuric acid type to a mixed type dominated by both sulfuric and nitric acid. The source identification indicated that SO42-, NO3-, NH4+ and F- were dominated by secondary sources, Mg2+, Ca2+ and Na+ mostly originated from natural sources, and K+ and Cl- probably associated with anthropogenic sources. Long-range transport of air masses could influence the acidity, electrical conductivity and ion concentrations of precipitation at SDZ. The higher acidity and ion concentrations mainly occurred in the southerly and westerly trajectory pathways and partially in northwest pathways. Anthropogenic pollutants and crustal sources along these pathways were significant contributors to the chemical composition of precipitation in SDZ.

High Contributions of Secondary Inorganic Aerosols to PM2.5 under Polluted Levels at a Regional Station in Northern China

Daily PM2.5 samples were collected at Shangdianzi (SDZ) regional site in Beijing–Tianjin–Hebei (BTH) region in 2015. Samples were subject to chemical analysis for organic carbon (OC), elemental carbon (EC), and major water-soluble inorganic ions. The annual average PM2.5 mass concentration was 53 ± 36 μg·m−3 with the highest seasonal average concentration in spring and the lowest in summer. Water-soluble inorganic ions and carbonaceous aerosols accounted for 34% ± 15% and 33% ± 9%, respectively, of PM2.5 mass on annual average. The excellent, good, lightly polluted, moderately polluted, and heavily polluted days based on the Air Quality Index (AQI) of PM2.5 accounted for 40%, 42%, 11%, 4%, and 3%, respectively, of the year. The sum of the average concentration of sulfate, nitrate, and ammonium (SNA) increased from 4.2 ± 2.9 μg·m−3 during excellent days to 85.9 ± 22.4 μg·m−3 during heavily polluted days, and their contributions to PM2.5 increased from 15% ± 8% to 49% ± 10% accordingly. In contrast, the average concentration of carbonaceous aerosols increased from 9.2 ± 2.8 μg·m−3 to 51.2 ± 14.1 μg·m−3, and their contributions to PM2.5 decreased from 34% ± 6% to 29% ± 7%. Potential source contribution function (PSCF) analysis revealed that the major sources for high PM2.5 and its dominant chemical components were within the area mainly covering Shandong, Henan, and Hebei provinces. Regional pollutant transport from Shanxi province and Inner Mongolia autonomous region located in the west direction of SDZ was also important during the heating season.

Observations of Atmospheric Δ14CO2 at the Global and Regional Background Sites in China: Implication for Fossil Fuel CO2 Inputs.

Six months to more than one year of atmospheric Δ14CO2 were measured in 2014-2015 at one global background site in Waliguan (WLG) and four regional background sites at Shangdianzi (SDZ), Lin'an (LAN), Longfengshan (LFS) and Luhuitou (LHT), China. The objectives of the study are to document the Δ14CO2 levels at each site and to trace the variations in fossil fuel CO2 (CO2ff) inputs at regional background sites. Δ14CO2 at WLG varied from 7.1 ± 2.9‰ to 32.0 ± 3.2‰ (average 17.1 ± 6.8‰) in 2015, with high values generally in autumn/summer and low values in winter/spring. During the same period, Δ14CO2 values at the regional background sites were found to be significantly (p < 0.05) lower than those at WLG, indicating different levels of CO2ff inputs at those sites. CO2ff concentrations at LAN (12.7 ± 9.6 ppm) and SDZ (11.5 ± 8.2 ppm) were significantly (p < 0.05) higher than those at LHT (4.6 ± 4.3 ppm) in 2015. There were no significant (p > 0.05) seasonal differences in CO2ff concentrations for the regional sites. Regional sources contributed in part to the CO2ff inputs at LAN and SDZ, while local sources dominated the trend observed at LHT. These data provide a preliminary understanding of atmospheric Δ14CO2 and CO2ff inputs for a range of Chinese background sites.

Key features of new particle formation events at background sites in China and their influence on cloud condensation nuclei

Long-term continuous measurements of particle number size distributions with mobility diameter sizes ranging from 3 to 800 nm were performed to study new particle formation (NPF) events at Shangdianzi (SDZ), Mt. Tai (TS), and Lin’an (LAN) stations representing the background atmospheric conditions in the North China Plain (NCP), Central East China (CEC), and Yangtze River Delta (YRD) regions, respectively. The mean formation rate of 3-nm particles was 6.3, 3.7, and 5.8 cm–3∙s–1, and the mean particle growth rate was 3.6, 6.0, and 6.2 nm∙h–1 at SDZ, TS, and LAN, respectively. The NPF event characteristics at the three sites indicate that there may be a stronger source of low volatile vapors and higher condensational sink of pre-existing particles in the YRD region. The formation rate of NPF events at these sites, as well as the condensation sink, is approximately 10 times higher than some results reported at rural/urban sites in western countries. However, the growth rates appear to be 1–2 times higher. Approximately 12%–17% of all NPF events with nucleated particles grow to a climaterelevant size (>50 nm). These kinds of NPF events were normally observed with higher growth rate than the other NPF cases. Generally, the cloud condensation nuclei (CCN) number concentration can be enhanced by approximately a factor of 2–6 on these event days. The mean value of the enhancement factor is lowest at LAN (2–3) and highest at SDZ (~4). NPF events have also been found to have greater impact on CCN production in China at the regional scale than in the other background sites worldwide.

Significant increase of surface ozone at a rural site, north of eastern China

Abstract. Ozone pollution in eastern China has become one of the top environmental issues. Quantifying the temporal trend of surface ozone helps to assess the impacts of the anthropogenic precursor reductions and the likely effects of emission control strategies implemented. In this paper, ozone data collected at the Shangdianzi (SDZ) regional atmospheric background station from 2003 to 2015 are presented and analyzed to obtain the variation in the trend of surface ozone in the most polluted region of China, north of eastern China or the North China Plain. A modified Kolmogorov–Zurbenko (KZ) filter method was performed on the maximum daily average 8 h (MDA8) concentrations of ozone to separate the contributions of different factors from the variation of surface ozone and remove the influence of meteorological fluctuations on surface ozone. Results reveal that the short-term, seasonal and long-term components of ozone account for 36.4, 57.6 and 2.2 % of the total variance, respectively. The long-term trend indicates that the MDA8 has undergone a significant increase in the period of 2003–2015, with an average rate of 1.13 ± 0.01 ppb year−1 (R2 = 0.92). It is found that meteorological factors did not significantly influence the long-term variation of ozone and the increase may be completely attributed to changes in emissions. Furthermore, there is no significant correlation between the long-term O3 and NO2 trends. This study suggests that emission changes in VOCs might have played a more important role in the observed increase of surface ozone at SDZ.

Evolution of surface O3 and PM2.5 concentrations and their relationships with meteorological conditions over the last decade in Beijing

In this study, hourly and daily records since 2005 and correlation, regression and composite methods were used to analyze the long-term evolution of surface O3 and PM2.5 concentrations at the rural station of Shangdianzi (SDZ) and urban station of Baolian (BL) over Beijing and their relationships with meteorological conditions. The results show that the mean concentrations of PM2.5 (O3) decreased (increased) at the urban and rural stations over the last decade. The linear trends of the annual mean concentrations of PM2.5 at BL and SDZ were −31.8 ug/m3/10yr (−4.3%/yr) (p < 0.01) and −13.3 ug/m3/10yr (−2.9%/yr) (p < 0.05), respectively. In winter, the mean wind speed (Ws) and relative humidity (RH) were the most closely correlated with O3 at both stations, whereas RH and sunshine hours (S) were most closely correlated with PM2.5. The correlation coefficients and explained variances in spring and autumn were generally less than those in winter and greater than those in summer. Moreover, increase in precipitation can significantly reduce the PM2.5 concentration in both urban and rural areas in Beijing, whereas trace and light precipitation more effectively decreases the O3 concentration. Concentrations of PM2.5 (O3) on haze days increased by 114% (3%) and 162% (20%) compared with that on non-haze days at the urban and rural stations, respectively. This result suggests that haze is a major manifestation of air pollution in Beijing.