Greenhouse gas observations from Cabauw Tall Tower (1992–2010)

Abstract. Since 1992 semi-continuous in-situ observations of greenhouse gas concentrations have been performed at the tall tower of Cabauw (4.927° E, 51.971° N, −0.7 m a.s.l.). Through 1992 up to now, the measurement system has been gradually extended and improved in precision, starting with CO2 and CH4 concentrations from 200 m a.g.l. in 1992 to vertical gradients at 4 levels of the gases CO2, CH4, SF6, N2O, H2, CO and gradients at 2 levels for 222Rn. In this paper the measurement systems and measurement results are described for the main greenhouse gases and CO, for the whole period. The automatic measurement system now provides half-hourly concentration gradients with a precision better than or close to the WMO recommendations. The observations at Cabauw show a complex pattern caused by the influence of sources and sinks from a large area around the tower with significant contributions of sources and sinks at distances up to 500–700 km. The concentration footprint area of Cabauw is one the most intensive and complex source areas of greenhouse gases in the world. Despite this, annual mean trends for the most important greenhouse gases, compatible with the values derived using the global network, can be reproduced from the measured concentrations at Cabauw over the entire measurement period, with a measured increase in the period 2000–2009 for CO2 of 1.90 ± 0.1 ppm yr−1, for CH4 of 4.4 ± 0.6 ppb yr−1, for N2O of 0.86 ± 0.04 ppb yr−1, and for SF6 of 0.27 ± 0.01 ppt yr−1; for CO no significant trend could be detected. The influences of strong local sources and sinks are reflected in the amplitude of the mean seasonal cycles observed at Cabauw, that are larger than the mean Northern Hemisphere average; Cabauw mean seasonal amplitude for CO2 is 25–30 ppm (higher value for lower sampling levels). The observed CH4 seasonal amplitude is 50–110 ppb. All gases except N2O show highest concentrations in winter and lower concentrations in summer, N2O observations show two additional concentration maxima in early summer and in autumn. Seasonal cycles of the day-time mean concentrations show that surface concentrations or high elevation concentrations alone do not give a representative value for the boundary layer concentrations, especially in winter time, but that the vertical profile data along the mast can be used to construct a useful boundary layer mean value. The variability at Cabauw in the atmospheric concentrations of CO2 on time scales of minutes to hours is several ppm and is much larger than the precision of the measurements (0.1 ppm). The diurnal and synoptical variability of the concentrations at Cabauw carry information on the sources and sinks in the footprint area of the mast, that will be useful in combination with inverse atmospheric transport model to verify emission estimates and improve ecosystem models. For this purpose a network of tall tower stations like Cabauw forms a very useful addition to the existing global observing network for greenhouse gases.

The ion chemistry and the source of PM2.5 aerosol in Beijing

Abstract. Quantifying historical trends in atmospheric greenhouse gases (GHGs) is important to understanding changes in their budgets and for climate modeling, which simulates historic and projects future climate. Archived samples analyzed using updated measurement techniques and calibration scales can reduce uncertainties in historic records of GHG mole fractions and their trends in time. Here, we present historical measurements of two important GHGs, nitrous oxide (N2O) and sulfur hexafluoride (SF6), collected at the midlatitude Northern Hemisphere station Cape Meares, Oregon (USA, 45.5∘ N, 124∘ W), between 1978 and 1996 in archived air samples from the Oregon Health and Science University – Portland State University (OHSU–PSU) air archive. N2O is the third most important anthropogenically forced GHG behind carbon dioxide (CO2) and methane (CH4). SF6 has a low abundance in the atmosphere, but is one of the most powerful GHGs known. Measurements of atmospheric N2O made during this period are available for select locations, but before mid-1990 they have larger uncertainties than more recent periods due to advancements made in gas chromatography (GC) methods. Few atmospheric SF6 measurements exist pre-1990, particularly in the Northern Hemisphere. The GC system used to measure N2O and SF6 mixing ratios in this work is designed to be fully automated, and is capable of running up to 15 samples per batch. Measurement precision (1σ) of N2O and SF6 is 0.16 % and 1.1 %, respectively (evaluated at 328.7 ppb and 8.8 ppt). Samples were corrected for detector response nonlinearity when measured against our reference standard, with the corrections determined to be 0.14 ppb ppb−1 in N2O and 0.03 ppt ppt−1 in SF6. The mixing ratio of N2O in archived samples is found to be 301.5±0.3 ppb in 1980 and rises to 313.5±0.3 ppb in 1996. The average growth rate over this period is 0.78±0.03 ppb yr−1 (95 % CI). The seasonal amplitude is statistically robust, with a maximum anomaly of 0.3 ppb near April and a minimum near November of −0.4 ppb. Measurements of N2O match well with previously reported values for Cape Meares and other comparable locations. The mixing ratio of SF6 in analyzed samples is found to be 0.85±0.03 ppt in 1980 and rises to 3.83±0.03 ppt in 1996. The average growth rate over this period is 0.17±0.01 ppt yr−1 (95 % CI). The seasonality is statistically robust and has an annual peak amplitude of 0.04 ppt near January and a minimum amplitude of −0.03 ppt near July. These are unique SF6 results from this site and represent a significant increase in the SF6 data available during the 1980s and early 1990s. The mixing ratio and growth rate of SF6 measured compares well to other Northern Hemisphere measurements over this period. From these N2O and SF6 measurements, we conclude that sample integrity is generally robust in the OHSU-PSU air archive for N2O and SF6.

The research of greenhouse gases on the Tibetan Plateau is of great importance since its unique topography as the third pole of our planet and profound response on the climate change. In this study, we compared the concurrent observations of atmospheric carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO) during 2010–2016 from two stations located on the Tibetan Plateau, which are Mt. Waliguan station (WLG), the only World Meteorological Organization/Global Atmosphere Watch global station in the inland of Eurasia, and Shangri‐La station, a Chinese national station (XGLL). Although both stations are located at remote area, the atmospheric CO2, CH4, and CO concentrations are frequently influenced by regional sources, especially for XGLL throughout the year and WLG in summer. Due to the unique topography and regional conditions, the atmospheric CH4 and CO at both stations display different trends with other sites in China, with higher values in summer. The atmospheric CO2, CH4, and CO at the XGLL mainly represent the conditions in regional scale. As the only World Meteorological Organization/Global Atmosphere Watch global station in the inland of Eurasia, the observation results at WLG can be used to represent the conditions on the Tibetan Plateau, but some of them are frequently influenced by the emissions from the cities located on the east or north east, and some even can be affect by emissions from the Ganges basin in autumn and winter, which should be treated with caution. By subtracting the influences of the cities, we updated the growth rate of 2.45 ± 0.02 ppm yr−1 for CO2, 8.2 ± 0.1 ppb yr−1 for CH4, and −0.4 ± 0.1 ppb yr−1 for CO, compared to the prior estimation of 2.31 ± 0.02 ppm yr−1 for CO2, 8.1 ± 0.1 ppb yr−1 for CH4, and −0.6 ± 0.1 ppb yr−1 for CO on the Tibetan Plateau.

Abstract. Results from the Trainou tall tower measurement station installed in 2006 are presented for atmospheric measurements of CO2, CH4, N2O, SF6, CO, H2 mole fractions and radon-222 activity. Air is sampled from four sampling heights (180, 100, 50 and 5 m) of the Trainou 200 m television tower in the Orléans forest in France (47°57'53" N, 2°06'45" E, 131 m a.s.l.). The station is equipped with a custom-built CO2 analyser (CARIBOU), which is based on a commercial non-dispersive, infrared (NDIR) analyser (Licor 6252), and a coupled gas chromatography (GC) system equipped with an electron capture detector (ECD) and a flame ionization detector (FID) (HP6890N, Agilent) and a reduction gas detector (PP1, Peak Performer). Air intakes, pumping and air drying system are shared between the CARIBOU and the GC systems. The ultimately achieved short-term repeatability (1 sigma, over several days) for the GC system is 0.05 ppm for CO2, 1.4 ppb for CH4, 0.25 ppb for N2O, 0.08 ppb for SF6, 0.88 ppb for CO and 3.8 for H2. The repeatability of the CARIBOU CO2 analyser is 0.06 ppm. In addition to the in situ measurements, weekly flask sampling is performed, and flask air samples are analysed at the Laboratoire des Sciences du Climat et de l'Environnement (LSCE) central laboratory for the same species as well for stable isotopes of CO2. The comparison between in situ measurements and the flask sampling showed averaged differences of 0.08 ± 1.40 ppm for CO2, 0.7 ± 7.3 ppb for CH4, 0.6 ± 0.6 ppb for N2O, 0.01 ± 0.10 ppt for SF6, 1.5± 5.3 ppb for CO and 4.8± 6.9 ppb for H2 for the years 2008–2012. At Trainou station, the mean annual increase rates from 2007 to 2011 at the 180 m sampling height were 2.2 ppm yr−1 for CO2, 4 ppb yr−1 for CH4, 0.78 ppb yr−1 for N2O and 0.29 ppt yr−1 for SF6. For all species, the 180 m sampling level showed the smallest diurnal variation. Mean diurnal gradients between the 50 m and the 180 m sampling level reached up to 30 ppm CO2, 15 ppm CH4 or 0.5 ppb N2O during nighttime whereas the mean gradients are smaller than 0.5 ppm for CO2 and 1.5 ppb for CH4 during afternoon.

Abstract. Located in north-east France, the Observatoire Pérenne de l'Environnement (OPE) station was built during the Integrated Carbon Observation System (ICOS) Demonstration Experiment to monitor the greenhouse gases mole fraction. Its continental rural background setting fills the gaps between oceanic or mountain stations and urban stations within the ICOS network. Continuous measurements of several greenhouse gases using high-precision spectrometers started in 2011 on a tall tower with three sampling inlets at 10, 50 and 120 m above ground level (a.g.l.). Measurement quality is regularly assessed using several complementary approaches based on reference high-pressure cylinders, audits using travelling instruments and sets of travelling cylinders (“cucumber” intercomparison programme). Thanks to the quality assurance strategy recommended by ICOS, measurement uncertainties are within the World Meteorological Organisation compatibility goals for carbon dioxide (CO2), methane (CH4) and carbon monoxide (CO). The time series of mixing ratios from 2011 to the end of 2018 are used to analyse trends and diurnal and seasonal cycles. The CO2 and CH4 annual growth rates are 2.4 ppm yr−1 and 8.8 ppb yr−1 respectively for measurements at 120 m a.g.l. over the investigated period. However, no significant trend has been recorded for CO mixing ratios. The afternoon mean residuals (defined as the differences between midday observations and a smooth fitted curve) of these three compounds are significantly stronger during the cold period when inter-species correlations are high, compared to the warm period. The variabilities of residuals show a close link with air mass back-trajectories.

Abstract. Numerous definitions and analytical techniques for elemental (or black) carbon (EC) have been published in the scientific literature, but still no generally accepted interdisciplinary definition exists. EC is not a single chemical compound, but is mainly composed of two parts of carbon contents: combustion residues from pyrolysis and combustion emissions formed via gas-to-particle conversion. Accordingly EC is subdivided into two classes: char and soot. Char is defined as carbonaceous materials obtained by heating organic substances and formed directly from pyrolysis, or as an impure form of graphitic carbon obtained as a residue when carbonaceous material is partially burned or heated with limited access of air. Soot is defined as only those carbon particles that form at high temperature via gas-phase processes. Since the different classes of EC have different chemical and physical properties, their optical light-absorbing properties differ, so that it is essential to differentiate them in the environment. The thermal optical reflectance (TOR) method was used to differentiate between char-EC and soot-EC according to its stepwise thermal evolutional oxidation of different carbon fractions under different temperatures and atmosphere. Char-EC and soot-EC are operationally defined as EC1-OP and EC2+EC3 (EC1, EC2 and EC3 corresponding to carbon fractions evolved at 550, 700 and 800 °C in a 98% He/2% O2 atmosphere, respectively), respectively. One year of observations of the daily and seasonal variations of carbonaceous particles were conducted in Xi'an, China in 2004 to demonstrate the different characteristics of char and soot in the atmosphere. Total carbon (TC), organic carbon (OC), EC and char-EC showed similar seasonal trends, with high concentrations in winter and low concentrations in summer, while soot-EC revealed relatively small seasonal variations, with maximum concentration (1.85±0.72 μg m−3) in spring and minimum concentration (1.15±0.47 μg m−3) in summer. The strong correlation between EC and char-EC (R2 = 0.99) and poor correlation between EC and soot-EC (R2 = 0.31) indicate that previously reported total EC in the literature reflected the distribution characteristics of char only, while overlooking that of soot. However, soot exhibits stronger light-absorbing characteristics than char, and merits greater focus in climate research. The small seasonal variation of soot-EC indicates that soot may be the background fraction in total EC, and is likely to have an even longer lifetime in the atmosphere than previously estimated for total EC, which suggests that soot may has a greater contribution to global warming. While both char-EC/soot-EC and primary OC/EC ratios vary with emission sources, only OC/EC ratio is affected by SOA. Thus char-EC/soot-EC may be a more effective indicator than OC/EC in source identification of carbonaceous aerosol. Comparison of seasonal variations of OC/EC and char-EC/soot-EC ratios in Xi'an confirms this point. However, wet scavenging by snow and rain was more effective for char than for soot and influenced the char-EC/soot-EC ratio, and this factor should be considered in source identification as well.

ABSTRACTWe developed an index to investigate the effect of transboundary air pollution (TAP) on the air quality of Kumamoto City, Japan. We estimated the effect of TAP by using the index and positive matrix factorization (PMF). Polycyclic aromatic hydrocarbons (PAHs) and trace metals were analyzed from the daily samples of the Total Suspended Particles (TSPs) collected seasonally from Oct. 2014 to Aug. 2015. These chemical components exhibited high concentrations in spring and winter, which is consistent with the data in the literature. Pb was identified as the TAP tracer owing to its high concentrations in winter and spring. Indeno(1, 2, 3-cd)pyrene (IcdP) was used as the local emission tracer in Kumamoto on the basis of previous studies. We applied the IcdP/Pb ratio as the index. The index enables the detection of TAP in daily data sets. PMF identified six factors: soil and road dust, biomass and waste burning, heavy oil combustion, fishing boats, vehicle emission, and coal combustion. The average contribution of TAP on the days when transboundary pollution was high was evaluated as being 46%.

The concentrations of atmospheric pollutants PM2.5, O3, SO2, NO2, and CO together with the meteorological factors of temperature （T）, relative humidity （RH）, wind speed, and other relevant data in Tangshan from 2015 to 2021 were collected to study the variation characteristics of PM2.5 and O3 at different periods in Tangshan City in the past seven years and their influencing factors, to discuss the contributions of air mass transport to PM2.5 and O3 pollution, and to reveal the synergistic influence mechanism of PM2.5 and O3 on atmospheric compound pollution by using correlation analysis and backward trajectory cluster analysis techniques. The results showed that PM2.5 concentrations in Tangshan decreased year by year from 2015 to 2021, whereas O3 concentration showed a unimodal trend, with the peak appearing in 2017. Both PM2.5 and O3 concentrations showed obvious seasonal variation trends； PM2.5 was characterized by the highest concentration in winter and the lowest concentration in summer, whereas O3 was characterized by the highest concentration in summer and the lowest concentration in winter. In addition, the diurnal variation in PM2.5 showed a bimodal distribution, with the peak occurring during the morning and evening on weekdays, and O3 showed a unimodal distribution, with the peak value appearing during the period with strong ultraviolet radiation in the afternoon. PM2.5 had a significant positive correlation with SO2, NO2, and CO, whereas O3 had a significant positive correlation with radiation and temperature. Under the different pollution conditions, PM2.5 and O3 were affected by air mass transports from different directions. Being impacted by various factors, the synergistic effect of PM2.5 and O3 on atmospheric compound pollution showed an obvious negative effect in winter, whereas there was an obvious positive effect in spring, summer, and autumn. Under the backgrounds of different pollutions, when the concentration of PM2.5 exceeded 150 μg·m-3, the synergistic effect of PM2.5 and O3 showed an obvious negative effect.

With the intention of contributing to a better understanding of snow depth profiles used in reconstructing the southern hemisphere nitrate background we have measured C1−, , and in firn cores from two coastal Antarctic locations (GvN = Ekströmisen 70°S, 8°W, and Filchner = Filchner-Ronne Ice Shelf 79°S, 57°W). The depth resolution chosen is 2 cm per sample (i.e. 36 and 14 samples per year, respectively).The isotopie composition of the firn cores was concurrently measured, with equally high resolution (deuterium and 18O data, W. Graf, private communication). The GvN core yields an average accumulation rate of 35 cm H2O per year during the period 1979–86, while the Filchner core gives 14 cm H2O per year during the period 1955-80. The net snow accumulation being relatively high allows precise determination of the year to year boundaries, as well as the relative contribution of individual seasons to the total net accumulation. This was achieved by combining the stable isotope data with the chemical tracers nss-sulfate (high concentration in summer) and sea salt (high C1− in autumn and winter). For the two individual locations this procedure allowed assessment of the glacial nitrate concentration seasonality as well as comparing the yearly nitrate deposition.The Filchner location shows a distinct seasonality with maximum concentrations in summer. For nearly half of the years covered we also find higher concentrations in winter. This higher nitrate in winter is always accompanied by high sea salt concentrations. We suggest therefore a mechanism making sea salt aerosol an additional deposition pathway for nitrate in winter. This means that we are not able to link the enhanced winter nitrate deposition to stratospheric denitrification directly. The GvN core does not show significant seasonality. This is presumably due to frequent snow drift events preventing signal conservation.Although the individual accumulation rates differ by a factor of 2.5 the yearly nitrate deposition is in the same range (4-11 kg (km-2 a-1) at both sites. This is caused by the different seasonal modulation of the net snow accumulation. At GvN low nitrate autumn precipitation prevails and keeps the yearly nitrate level constantly low (18-22 ppb). At Filchner, however, a high contribution of summer snow brings the yearly concentration average up to about 30–70 pbb.

Size-resolved filter samples were collected in Sanya every other week from June 2012 to May 2014. The mass concentrations of water-soluble inorganic ions, including anions (Cl-, NO3-, SO42-) and cations (Na+, NH4+, K+, Mg2+, Ca2+) were measured by ion chromatography. The results showed that the total concentrations of measured water-soluble inorganic ions were (8.91±7.27) and (11.34±9.37) μg·m-3 in PM2.1 and PM2.1-9, respectively. In PM2.1, SO42- and NH4+ comprised 72.2% of all water-soluble inorganic ions, while in PM2.1~9, Cl-, Ca2+ and Na+ comprised 67.6% of all water-soluble inorganic ions. In PM2.1, the total concentrations of water-soluble inorganic ions had highest concentrations in winter and lowest concentrations in summer. In PM2.1~9, the total concentrations of water-soluble inorganic ions presented the highest concentrations in summer. SO42- and NH4+ showed bimodal size distributions and the peaks in the fine mode shifted from 0.43-0.65 μm in spring, summer and autumn to 0.65-1.1 μm in winter. NO3-, Na+, Cl-, Ca2+ and Mg2+ were unimodal with the peaks in the coarse mode of 4.7-9.0 μm. K+ showed bimodal size distribution with the fine mode at 0.43-0.65 μm and the coarse mode at 4.7-5.8 μm. PCA analysis showed that water-soluble inorganic ions were mainly affected by the secondary formation, sea salt and soil particles or falling dust.

With the intention of contributing to a better understanding of snow depth profiles used in reconstructing the southern hemisphere nitrate background we have measured C1−, , and in firn cores from two coastal Antarctic locations (GvN = Ekströmisen 70°S, 8°W, and Filchner = Filchner-Ronne Ice Shelf 79°S, 57°W). The depth resolution chosen is 2 cm per sample (i.e. 36 and 14 samples per year, respectively). The isotopie composition of the firn cores was concurrently measured, with equally high resolution (deuterium and 18O data, W. Graf, private communication). The GvN core yields an average accumulation rate of 35 cm H2O per year during the period 1979–86, while the Filchner core gives 14 cm H2O per year during the period 1955-80. The net snow accumulation being relatively high allows precise determination of the year to year boundaries, as well as the relative contribution of individual seasons to the total net accumulation. This was achieved by combining the stable isotope data with the chemical tracers nss-sulfate (high concentration in summer) and sea salt (high C1− in autumn and winter). For the two individual locations this procedure allowed assessment of the glacial nitrate concentration seasonality as well as comparing the yearly nitrate deposition. The Filchner location shows a distinct seasonality with maximum concentrations in summer. For nearly half of the years covered we also find higher concentrations in winter. This higher nitrate in winter is always accompanied by high sea salt concentrations. We suggest therefore a mechanism making sea salt aerosol an additional deposition pathway for nitrate in winter. This means that we are not able to link the enhanced winter nitrate deposition to stratospheric denitrification directly. The GvN core does not show significant seasonality. This is presumably due to frequent snow drift events preventing signal conservation. Although the individual accumulation rates differ by a factor of 2.5 the yearly nitrate deposition is in the same range (4-11 kg (km-2 a-1) at both sites. This is caused by the different seasonal modulation of the net snow accumulation. At GvN low nitrate autumn precipitation prevails and keeps the yearly nitrate level constantly low (18-22 ppb). At Filchner, however, a high contribution of summer snow brings the yearly concentration average up to about 30–70 pbb.

Aim(a) To determine the spatial distributions and levels of major and minor elements, as well as heavy metals, in water, sediment, and biota (plant and fish) in Al-Hammar Marsh, southern Iraq, and ultimately to supply more comprehensive information for policy-makers to manage the contaminants input into the marsh so that their concentrations do not reach toxic levels. (b) to characterize the seasonal changes in the marsh surface water quality. (c) to address the potential environmental risk of these elements by comparison with the historical levels and global quality guidelines (i.e., World Health Organization (WHO) standard limits). (d) to define the sources of these elements (i.e., natural and/or anthropogenic) using combined multivariate statistical techniques such as Principal Component Analysis (PCA) and Agglomerative Hierarchical Cluster Analysis (AHCA) along with pollution analysis (i.e., enrichment factor analysis)MethodsWater, sediment, plant, and fish samples were collected from the marsh, and analyzed for major and minor ions, as well as heavy metals, and then compared to historical levels and global quality guidelines (WHO guidelines). Then, multivariate statistical techniques, such as PCA and AHCA, were used to determine the element sourcing.ResultsWater analyses revealed unacceptable values for almost all physio-chemical and biological properties, according to WHO standard limits for drinking water. Almost all major ions and heavy metal concentrations in water showed a distinct decreasing trend at the marsh outlet station compared to other stations. In general, major and minor ions, as well as heavy metals exhibit higher concentrations in winter than in summer. Sediment analyses using multivariate statistical techniques revealed that Mg, Fe, S, P, V, Zn, As, Se, Mo, Co, Ni, Cu, Sr, Br, Cd, Ca, N, Mn, Cr, and Pb were derived from anthropogenic sources, while Al, Si, Ti, K, and Zr were primarily derived from natural sources. Enrichment factor analysis gave results compatible with multivariate statistical techniques findings. Analysis of heavy metals in plant samples revealed that there is no pollution in plants in Al-Hammar Marsh. However, the concentrations of heavy metals in fish samples showed that all samples were contaminated by Pb, Mn, and Ni, while some samples were contaminated by Pb, Mn, and Ni.Discussion and conclusionsDecreasing of Tigris and Euphrates discharges during the past decades due to drought conditions and upstream damming, as well as the increasing stress of wastewater effluents from anthropogenic activities, led to degradation of the downstream Al-Hammar Marsh water quality in terms of physical, chemical, and biological properties. As such properties were found to consistently exceed the historical and global quality objectives. However, element concentration decreasing trend at the marsh outlet station compared to other stations indicate that the marsh plays an important role as a natural filtration and bioremediation system. Higher element concentrations in winter were due to runoff from the washing of the surrounding Sabkha during flooding by winter rainstorms. Finally, the high concentrations of heavy metals in fish samples can be attributed to bioaccumulation and biomagnification processes.

As an important component of atmospheric aerosols, black carbon (BC) has a great influence on the regional and global radiation balance, climate, and human health due to its small particle size, large specific surface area, and radiative forcing potential. Here, the spatio-temporal characteristics of atmospheric BC were investigated based on modern-era retrospective analysis for research and applications version 2 (MERRA-2) reanalysis data and ground observation data during 1980-2019 in Shanghai, a highly urbanized city in mainland China. The influences of local emissions and regional transmission on regional-scale BC concentrations were examined using the M-K trend test, backward trajectory analysis, and the potential source contribution function (PSCF). The results showed that:① MERRA-2 BC and ground observation datasets showed good consistency (R∈[0.68, 0.72]), indicating that MERRA-2 reanalysis data can be used to reveal long-term changes in ground-level atmospheric BC concentrations; ② Atmospheric BC concentrations in Shanghai over the past 40 years can be divided into three stages:a "low value" stage of slow growth[1980-1986, (1.75±0.17) μg·m-3], a relatively stable "median value" stage[1987-1999, (2.18 ±0.07) μg·m-3], and a fluctuating "high value" stage[2000-2019, (3.07±0.31) μg·m-3]. Seasonally, Shanghai's BC concentrations generally show a "U" pattern with low concentrations in summer and high concentrations in winter. As a result of black carbon emissions from marine diesel engines and other engines used for water transportation, a small peak also occurs in July; ③ The diagnostic quality ratio of air pollutants and the bivariate correlation analysis[R(BC-NO2)>R(BC-CO)>R(BC-SO2)] indicated that traffic emissions were the main sources of atmospheric BC in Shanghai, especially by heavy diesel vehicles; ④ The backward trajectory and PSCF analyses found that the air mass of Shanghai in summer was dominated by a clean sea breeze, accounting for 77.18%. In contrast, during the other seasons, more than 50% of the air mass came from the north. The potential source regions of atmospheric BC in Shanghai are mainly distributed in eastern China, expanding outwards and centering on the Yangtze River Delta, and the expansion direction is consistent with the directions of the backward trajectories.

Due to its urgency, curbing greenhouse gas (GHG) emissions as fast as possible is pivotal for all countries. Mitigation measures are being initiated and a need for monitoring verification and reporting (MVR) of their efficacy arises. Currently existing science based MVR strategies are either too fine scale, e.g. traditional eddy covariance, or very coarse scale, e.g., atmospheric model inversion from high precision continental scale concentration fields. Integral methods to estimate GHG budgets of landscapes and cities are in the state of development. One element of such systems are turbulent flux measurements from tall tower platforms. To be able to document the green transition of Denmark in terms of reducing GHG budgets, we proposed a network of tall tower GHG flux measurements covering representative urban and remote landscapes. In the first step of the project, we designed and built a prototype of such system and applied it in a rural area close to the Danish Capital of Copenhagen. In this presentation, we define criteria for a successful tall tower based GHG flux observation system for MVR of a change in net GHG emissions. We provide a brief overview how we optimized the design to meet these criteria. Finally, we present some key results from the first five months of continuous observation to demonstrate how well we actually met the criteria with our system and conclude on the future prospects of the proposed tall tower GHG observation network. The results include net fluxes of all major long living GHG (CO2, CH4 and N2O) and two indicator gasses, i.e. carbonyl sulfide (COS) and carbon monoxide (CO). These indicator gases were chosen to represent photosynthesis and to estimate fossil CO2 fluxes from combustion processes. Important results are how accurate the data represent the landscape and what the detection limits for flux estimations of the different GHGs are.