Atmospheric Monitoring Sites Research Articles

Cause of nocturnal surface ozone enhancement in the North China Plain

The North China Plain (NCP), known for its dense population, extensive urbanization, and developed industry and agriculture, faces one of the foremost ozone (O3) pollution issues nationwide and even globally. Currently, most studies focus on daytime peak O3 levels, with insufficient understanding of the increase in nighttime O3 concentrations. Based on data from 204 national atmospheric composition monitoring sites in the NCP from 2015 to 2023, we investigated the characteristics of nocturnal surface O3 enhancement (NSOE) events and explored potential formation mechanisms. The mean annual frequencies of single-site and regional NSOE event in the NCP between 2015 and 2023 are 42 % and 21 %, respectively. The daytime peak O3 concentrations before and after NSOE events exceeded those during the corresponding periods of non-NSOE events by 84 ± 19 and 32 ± 15 μg/m3, respectively. The overall effect of the NSOE events was to decelerate the rate of decline in nighttime O3 concentrations and resulted in a reduction of NO2 and CO concentrations from 22:00 onwards. Low level jet (LLJ) and vertical mixing were the main factors affecting NSOE events in the NCP. The proportion of NSOE events affected by LLJ in four representative cities ranged from 57.6 % to 79.5 %. Furthermore, the high concentration of O3 in the residual layer before the NSOE event and the reduction of atmospheric stability during the NSOE event favored downward mixing of upper layer O3. The primary weather systems influencing the four most severe regional NSOE events were LLJ, typhoon, and cold fronts. The first two events were dominated by vertical mixing of O3, while the latter two events were mainly affected by horizontal transport. Our findings provide the first overview of NSOE events in the NCP from characteristics to mechanisms, emphasizing the necessity for future detailed studies based on nocturnal vertical O3 observations.

Using in situ measurements of δ13C in methane to investigate methane emissions from the western Canada sedimentary basin

During COP26, Canada joined the Global Methane Pledge aiming to reduce global methane (CH4) emissions by 30% below 2020 levels by 2030. Rapid reduction of anthropogenic CH4 emissions in the atmosphere is considered one of the most effective strategies to slow global warming in concert with carbon dioxide mitigation measures. In Canada, a large part of anthropogenic CH4 emissions can be attributed to the oil and gas industry in the Western Canada Sedimentary Basin (WCSB), which is the fourth largest reserve of fossil fuel in the world. Recent studies highlighted big discrepancies between CH4 emissions reported in Canada's National Inventory and emissions estimated with approaches using atmospheric measurements for the oil and gas sector. Measuring the isotopic signature of CH4 (δ13CH4) at different atmospheric monitoring stations and comparing these measurements to detailed archives of δ13CH4 from oil and gas wells and associated CH4 leaks in the WCSB could help better characterize the emissions from different CH4 sources over the region. In this study, we compare two independent sets of data: (1) thousands of δ13CH4 of samples from oil and gas production wells and their associated leaks (surface casing vents and ground migration) collected across the WCSB, and (2) atmospheric mixing ratios of CH4 and their δ13CH4 measured successively at three locations across this region between 2016 and 2020 combined with their atmospheric footprints modeled with HYSPLIT-STILT. We observed a gradient in the isotopic signatures of the oil and gas samples within the WCSB with δ13CH4 being more depleted in the Southeast than in the Northwest. The analysis of these samples showed that the isotopic signature of CH4 emitted by the production of fossil fuel depends on the geological formations from which it is extracted. Also, CH4 isotopic signatures vary more depending on the region where CH4 comes from than on the type of fossil fuel extracted (natural gas, oil, heavy oil, shale gas). The atmospheric measurements showed a strong seasonality of δ13CH4 at one of the atmospheric monitoring sites with isotopic signatures associated with thermogenic sources in winter and isotopic signatures associated with a mix of biogenic and thermogenic sources in summer. Using the δ13CH4 archive database from oil and gas samples, we estimated that 28–39 % of the CH4 emitted near this site in summer was coming from a biogenic source (most likely wetlands). Ultimately, atmospheric measurements collected during winter combined with their associated HYSPLIT-STILT footprints presented a spatial distribution of δ13CH4 over the WCSB comparable to the one observed in the archive database from the oil and gas sector, confirming that the oil and gas sector is the main source of CH4 in this region.

Air pollutant prediction model based on transfer learning two-stage attention mechanism

Atmospheric pollution significantly impacts the regional economy and human health, and its prediction has been increasingly emphasized. The performance of traditional prediction methods is limited due to the lack of historical data support in new atmospheric monitoring sites. Therefore, this paper proposes a two-stage attention mechanism model based on transfer learning (TL-AdaBiGRU). First, the first stage of the model utilizes a temporal distribution characterization algorithm to segment the air pollutant sequences into periods. It introduces a temporal attention mechanism to assign self-learning weights to the period segments in order to filter out essential period features. Then, in the second stage of the model, a multi-head external attention mechanism is introduced to mine the network's hidden layer key features. Finally, the adequate knowledge learned by the model at the source domain site is migrated to the new site to improve the prediction capability of the new site. The results show that (1) the model is modeled from the data distribution perspective, and the critical information within the sequence of periodic segments is mined in depth. (2) The model employs a unique two-stage attention mechanism to capture complex nonlinear relationships in air pollutant data. (3) Compared with the existing models, the mean absolute error (MAE), root mean square error (RMSE), and mean absolute percentage error (MAPE) of the model decreased by 14%, 13%, and 4%, respectively, and the prediction accuracy was greatly improved.

Southern Hemisphere atmospheric history of carbon monoxide over the late Holocene reconstructed from multiple Antarctic ice archives

Abstract. Carbon monoxide (CO) is a naturally occurring atmospheric trace gas, a regulated pollutant, and one of the main components determining the oxidative capacity of the atmosphere. Evaluating climate–chemistry models under different conditions than today and constraining past CO sources requires a reliable record of atmospheric CO mixing ratios ([CO]) that includes data since preindustrial times. Here, we report the first continuous record of atmospheric [CO] for Southern Hemisphere (SH) high latitudes over the past 3 millennia. Our continuous record is a composite of three high-resolution Antarctic ice core gas records and firn air measurements from seven Antarctic locations. The ice core gas [CO] records were measured by continuous flow analysis (CFA), using an optical feedback cavity-enhanced absorption spectrometer (OF-CEAS), achieving excellent external precision (2.8–8.8 ppb; 2σ) and consistently low blanks (ranging from 4.1±1.2 to 7.4±1.4 ppb), thus enabling paleo-atmospheric interpretations. Six new firn air [CO] Antarctic datasets collected between 1993 and 2016 CE at the DE08-2, DSSW19K, DSSW20K, South Pole, Aurora Basin North (ABN), and Lock-In sites (and one previously published firn CO dataset at Berkner) were used to reconstruct the atmospheric history of CO from ∼1897 CE, using inverse modeling that incorporates the influence of gas transport in firn. Excellent consistency was observed between the youngest ice core gas [CO] and the [CO] from the base of the firn and between the recent firn [CO] and atmospheric [CO] measurements at Mawson station (eastern Antarctica), yielding a consistent and contiguous record of CO across these different archives. Our Antarctic [CO] record is relatively stable from −835 to 1500 CE, with mixing ratios within a 30–45 ppb range (2σ). There is a ∼5 ppb decrease in [CO] to a minimum at around 1700 CE during the Little Ice Age. CO mixing ratios then increase over time to reach a maximum of ∼54 ppb by ∼1985 CE. Most of the industrial period [CO] growth occurred between about 1940 to 1985 CE, after which there was an overall [CO] decrease, as observed in Greenland firn air and later at atmospheric monitoring sites and attributed partly to reduced CO emissions from combustion sources. Our Antarctic ice core gas CO observations differ from previously published records in two key aspects. First, our mixing ratios are significantly lower than reported previously, suggesting that previous studies underestimated blank contributions. Second, our new CO record does not show a maximum in the late 1800s. The absence of a [CO] peak around the turn of the century argues against there being a peak in Southern Hemisphere biomass burning at this time, which is in agreement with (i) other paleofire proxies such as ethane or acetylene and (ii) conclusions reached by paleofire modeling. The combined ice core and firn air [CO] history, spanning −835 to 1992 CE, extended to the present by the Mawson atmospheric record, provides a useful benchmark for future atmospheric chemistry modeling studies.

Climatology of aerosol properties at an atmospheric monitoring site on the northern California coast

Abstract. Between April 2002 and June 2017, the Global Monitoring Laboratory (GML) of the National Oceanic and Atmospheric Administration (NOAA) made continuous measurements of a suite of in situ aerosol optical properties at a long-term monitoring site near Trinidad Head (THD), California. In addition to aerosol optical properties, between 2002–2006 a scanning humidograph system was operated, and inorganic ion and total aerosol mass concentrations were obtained from filter measurements. A combined analysis of these datasets demonstrates consistent patterns in aerosol climatology and highlights changes in sources throughout the year. THD is predictably dominated by sea salt aerosols; however, marine biogenic aerosols are the largest contributor to PM1 in the warmer months. Additionally, a persistent combustion source appears in the winter, likely a result of wintertime home heating. While the influences of local anthropogenic sources from vehicular and marine traffic are visible in the optical aerosol data, their influence is largely dictated by the wind direction at the site. Comparison of the THD aerosol climatology to that reported for other marine sites shows that the location is representative of clean marine measurements, even with the periodic influence of anthropogenic sources.

The Z-2018 emissions inventory of COS in Europe: A semiquantitative multi-data-streams evaluation

The anthropogenic emissions of carbonyl sulfide (COS) and the uptake of this gas by terrestrial vegetation are major drivers of COS concentration variations in the atmosphere since the beginning of the industrial era. The fine spatial resolution (i.e., 0.1° × 0.1°) of the gridded anthropogenic emissions inventory of COS developed by Zumkehr et al. (2018), Z-2018 hereafter, is designed for a use by regional chemistry-transport models. In order to anticipate future applications at the regional scale, we carried out a first semiquantitative assessment of direct and indirect (i.e., from CS2 conversion) COS anthropogenic emissions at the sub-country scale in France using historical governmental data. Better agreement between the two inventories was found for direct emissions of COS by coal power plants, than for indirect sources. The use in this latter case of a sub-country spatial scaling, based on industrial N2O emissions, (1) strongly underestimates fluxes from food casings and cellulosic sponge industrial activities responsible for atmospheric CS2 emissions in France, and (2) considerably overestimates emissions from Paris and surrounding areas, which are free of a rayon industry. A list of food casings and cellulosic sponge industrial sites is provided to produce a more realistic inventory of CS2 sources in Europe. Nevertheless, a cluster analysis of wintertime air masses trajectories, with the atmospheric COS monitoring site of Gif-sur-Yvette (GIF) as end point, suggests that Z-2018 correctly identifies northern Germany and Belgium as sources of anthropogenic COS. In winter, when the wind blows from the NE sector, advection of anthropogenic COS from coal power plants is illustrated by synchronous variations in GIF and at the Trainou tall tower (distant of about 80 km) of a series of atmospheric pollution tracers, especially between COS and sulfates. These observations support the use of SO2 emissions as temporal and sub-country spatial scaling factors of COS emissions by the coal industry.

Impacts of the COVID-19 lockdown in China on new particle formation and particle number size distribution in three regional background sites in Asian continental outflow

Despite the curtailment of atmospheric condensing precursor gases during the Coronavirus disease 2019 (COVID-19) lockdown (LD) period, unexpected haze events via the formation of new particles and their subsequent growth have been identified. This study investigated the impact of emission reduction during the Chinese LD period on the new particle formation (NPF) frequency and corresponding particle number size distribution (PNSD) at three regional background atmospheric monitoring sites in the western coastal areas of the Korean Peninsula. During this duration, the number concentrations of the nucleation- (<25 nm) and accumulation-mode (>90 nm) particles significantly decreased in Baengryeong (BRY), showing decreases of 34% and 29%, respectively. Unlike BRY, the PNSD in Anmyeon (AMY), which is influenced by nearby industrial emissions, remained nearly unchanged during the LD period, possibly because the reduction in industrial emissions was not significant during the social distancing period enforced by Korea. Bongseong (BOS) showed a similar variation to that of BRY; however, the magnitude of the reduction was weaker because of its higher altitude compared to other sites. The cyclostationary empirical orthogonal function technique was applied to the measured PNSDs at the three sites to objectively classify NPF events. Because mode 1 of cyclostationary loading vectors commonly represented the typical diurnal variation of PNSD during regional NPF events at three sites, mode 1 of the corresponding principal component time series was used for NPF classification. The NPF frequency decreased by 7%, 1%, and 7% in BRY, AMY, and BOS, respectively, despite favorable meteorological conditions, such as increased temperature and insolation during the LD period. The diurnal variation in the sulfuric acid (H2SO4) proxy implied that the H2SO4 proxy acted as a determining factor for NPF events during the NPF occurrence time (8–12 local hours) in AMY and BOS; however, NPF occurrence in BRY was not connected to the H2SO4 proxy level. This suggests that BRY was more likely to be influenced by the reduction in organic species in the continental upwind regions, while the occurrence of NPF events in AMY and BOS can be suppressed in association with the distinct reduction in inorganic compounds represented by the H2SO4 proxy during the LD period.

Atmospheric CO2 and CH4 Fluctuations over the Continent-Sea Interface in the Yenisei River Sector of the Kara Sea

Observations of the atmospheric sources and sinks of carbon dioxide (CO2) and methane (CH4) in the pan-Arctic domain are extremely scarce, limiting our knowledge of carbon turnover in this climatically sensitive environment and the fate of the enormous carbon reservoirs conserved in the permafrost. Especially critical are the gaps in the high latitudes of Siberia, covered by the vast permafrost underlain tundra, where only several atmospheric monitoring sites are operational. This paper presents the first two years (September 2018–January 2021) of accurate continuous observations of atmospheric CO2 and CH4 dry mole fractions at the recently deployed tower-based measurement station “DIAMIS” (73.5068° N, 80.5198° E) located on the southwestern coast of the Taimyr Peninsula, Siberia, at the Gulf of the Yenisei River that opens to the Kara Sea (Arctic Ocean). In this paper, we summarized the scientific rationale of the site, examined the seasonal footprint of the station with an analysis of terrestrial vegetation and maritime sector contributing to the captured atmospheric signal, and illustrated temporal patterns of CO2 and CH4 for the daytime mixed atmospheric layer over the continent–sea interface. Along with the temporal variations reflecting a signal caused pan-Arctic and not very much influenced by the local processes, we analyzed the spatiotemporal distribution of the synoptic anomalies representing the atmospheric signatures of regional sources and sinks of CO2 and CH4 for the studied high-arctic Siberian domain of ~625 thousand km2, with nearly equal capturing the land surface (54%) and the ocean (46%) throughout the year. Both for CO2 and CH4, we have observed a sea–continent declining trend, presuming a larger depletion of trace gases in the maritime air masses compared to the continental domain. So far, over the Kara Sea, we have not detected any prominent signals of CH4 that might have indicated processes of subsea permafrost degradation and occurrence of cold seeps–still mainly observed in the eastern Arctic Seas—The Laptev Sea and the East-Siberian Sea.

Short communication The Outbreak of the COVID-19 Pandemic and its Healing Effects on the Environment

COVID 19, the virus which originated from a wet market in Wuhan, China. Since its exposure in December, 2019, the virus has spread to almost all the countries in the world, thus turning an epidemic into a pandemic. Although COVID 19 has taken a massive toll on the Human health and global economy, its outbreak has shown positive impacts on the environmental air quality. As the majority of the world is under lock down, the global air pollution has reduced by 40 percent during April 2020. This was identified with the assistance of the data collected from European and American Atmospheric monitoring sites. This article thus summarizes the positive effects of lock down and reduced human mobility, towards the improvement of environmental air quality.

Boreas: A Sample Preparation-Coupled Laser Spectrometer System for Simultaneous High-Precision In Situ Analysis of δ13C and δ2H from Ambient Air Methane.

We present a new instrument, “Boreas”, a cryogen-free methane (CH4) preconcentration system coupled to a dual-laser spectrometer for making simultaneous measurements of δ13C(CH4) and δ2H(CH4) in ambient air. Excluding isotope ratio scale uncertainty, we estimate a typical standard measurement uncertainty for an ambient air sample of 0.07‰ for δ13C(CH4) and 0.9‰ for δ2H(CH4), which are the lowest reported for a laser spectroscopy-based system and comparable to isotope ratio mass spectrometry. We trap CH4 (∼1.9 μmol mol–1) from ∼5 L of air onto the front end of a packed column, subsequently separating CH4 from interferences using a controlled temperature ramp with nitrogen (N2) as the carrier gas, before eluting CH4 at ∼550 μmol mol–1. This processed sample is then delivered to an infrared laser spectrometer for measuring the amount fractions of 12CH4, 13CH4, and 12CH3D isotopologues. We calibrate the instrument using a set of gravimetrically prepared amount fraction primary reference materials directly into the laser spectrometer that span a range of 500–626 μmol mol–1 (CH4 in N2) made from a single pure CH4 source that has been isotopically characterized for δ13C(CH4) by IRMS. Under the principle of identical treatment, a compressed ambient air sample is used as a working standard and measured between air samples, from which a final calibrated isotope ratio is calculated. Finally, we make automated measurements of both δ13C(CH4) and δ2H(CH4) in over 200 ambient air samples and demonstrate the application of Boreas for deployment to atmospheric monitoring sites.

Spatial and temporal variation characteristics of atmospheric NO2 and SO2 in the Beijing-Tianjin-Hebei region before and after the COVID-19 outbreak.

Emergency response mechanisms were activated throughout China during the COVID-19 outbreak. It is different from the temporary, partial, and limited pollution control measures taken to ensure the regional environmental quality during several important events such as the 2008 Beijing Olympic Games and the 2014 Asia-Pacific Economic Cooperation (APEC). During the COVID-19 epidemic period, extensive movement of people and almost all unnecessary industrial production (necessary industrial production refers to the production of food, epidemic prevention materials, etc.) have been severely restricted, so transportation and industrial production have been greatly reduced. This is a rare extreme emission reduction scenario that presents a unique opportunity for atmospheric research. In this study, based on hourly mass concentration data of NO2 and SO2 from atmospheric monitoring sites in the Beijing-Tianjin-Hebei (BTH) region during the COVID-19 epidemic period, the changes in transportation and industrial production in the region, data statistics, and spatial analysis were used to analyze the pollution changes and their causes. The results indicate that the NO2 and SO2 concentrations in the BTH region decreased significantly during the epidemic period. The spatial distribution pattern of NO2 pollution in the BTH region was “high in the southeast and low in the northwest,” and SO2 pollution in the BTH region was high in the southern and eastern parts of Hebei. The initiation of emergency response level 1 had an obvious effect on reducing NO2 and SO2 pollution in the region, while the impact of emergency response level 2 and below was limited. Compared with the single traffic control, the comprehensive control, similar to the emergency response, had a better effect on reducing NO2 pollution in the region. The control of major large cities in the region also had a certain effect on alleviating NO2 and SO2 pollution in the entire region. Moreover, for activities under short-term control, it is particularly important to guard against the “retaliatory growth” after the control is lifted. By reducing and controlling some polluting industries in industrial production, the degree of NO2 and SO2 pollution in the region can be effectively reduced. The manufacturing industry of chemical raw materials and the chemical products and non-metallic mineral products industry made a great contribution to the change in industrial source pollution emissions in the BTH region during the COVID-19 epidemic. Road traffic emissions remained an important source of NO2 emissions in the BTH region during this period. NO2 emission reduction can be effectively achieved by controlling road traffic and transportation.

Relationship between Atmospheric PM-Bound Reactive Oxygen Species, Their Half-Lives, and Regulated Pollutants: Investigation and Preliminary Model.

The concentration, nature, and persistence of particulate matter (PM)-bound reactive oxygen species (ROS) are of significant interest in understanding how atmospheric pollution affects health. However, the inherent difficulties in their measurement, particularly regarding the so-called "short-lived" ROS, have limited our understanding of their persistence and concentrations in the atmosphere. This paper aims to address this limitation through the analysis of PM-bound ROS measurements from the Particle Into Nitroxide Quencher (PINQ) system at an atmospheric monitoring site in the city of Heshan, Guangdong Province, China. The measured daily average and standard deviation for the measurement period was 0.050 ± 0.017 nmol·m-3. The averaged measured concentration of ROS per mass of PM and standard deviation was 0.0012 ± nmol·mg. The dataset was also correlated with standard pollutants, and a simplified model was constructed to separate the contributions of short-lived (t1/2 = 5 min) and long-lived (t1/2 ∼ infinity) ROS to total concentration using ozone, carbon monoxide, and PM mass. This showed that the short-lived ROS contribute an average of 33% of the daily PM-bound ROS burden over the measurement period, up to 52% of daily average on elevated days, and up to 71% for hourly averages. These results highlight the need for accurate measurements of short-lived ROS and provide the starting point for a general model to predict PM-bound ROS concentrations using widely available standard pollutants for future epidemiological research.

Retrieval of NO2 density using diffused solar radiation from buildings

A proposed method for monitoring near ground NO2 density using diffused radiation from buildings is based on two assumptions: 1) the refractive index of the buildings is of a low frequency compared to the wavelength; and 2) for a given narrow range of distances, the horizon distribution of NO2 is approximately uniform. Based on these two assumptions, the NO2 density of Chengdu was calculated, the results of which are very close to the corresponding data from the atmospheric monitoring site, proving the method is feasible.

Public perception of smog: A case study in Ningbo City, China

ABSTRACTSmog has become a public environmental crisis in most areas of China, and in response, research efforts have mainly focused on the chemical properties of smog and its impact on human health. However, in-depth research on the public’s perception of smog has not yet been conducted. A survey of residents living around eight state-controlled atmospheric environmental monitoring sites in Ningbo City was conducted using stratified sampling. The data was statistically analyzed to investigate people’s views and behavioral tendencies in smog weather, the influence of different media reports on public outlook, and public opinions on the local atmosphere and pollution management in different areas. The results showed that people’s perception of smog differs greatly from actual conditions, indicating that the public opinion tends to deviate when faced with a public crisis. Mainstream media (TV, newspaper, etc.), accounting for 67% of all media sources, are the main source for dissemination of smog information. The main sources of pollution, in order of decreasing contribution, according to residents of Ningbo City are as follows: motor vehicle exhaust, industrial coal combustion, large-scale construction, biomass burning, and kitchen fumes.Implications: Since 2011, most areas of China have been affected by frequent smog. Most research on smog has been concentrated on its causes, alert systems, and prevention measures, whereas in-depth research on the public perception of smog has not yet been conducted. When a risky environmental event such as smog occurs, consequences may be more serious than the event itself will cause if people take irrational measures because of lacking relevant knowledge. Therefore, investigating people’s attitude and response to smog is both theoretically and practically significant.

Analysis of Urban Effects in Oklahoma City using a Dense Surface Observing Network

AbstractMany studies have investigated urban heat island (UHI) intensity for cities around the world, which is normally quantified as the temperature difference between urban location(s) and rural location(s). A few open questions still remain regarding the UHI, such as the spatial distribution of UHI intensity, temporal (including diurnal and seasonal) variation of UHI intensity, and the UHI formation mechanism. A dense network of atmospheric monitoring sites, known as the Oklahoma City (OKC) Micronet (OKCNET), was deployed in 2008 across the OKC metropolitan area. This study analyzes data from OKCNET in 2009 and 2010 to investigate OKC UHI at a subcity spatial scale for the first time. The UHI intensity exhibited large spatial variations over OKC. During both daytime and nighttime, the strongest UHI intensity is mostly confined around the central business district where land surface roughness is the highest in the OKC metropolitan area. These results do not support the roughness warming theory to explain the air temperature UHI in OKC. The UHI intensity of OKC increased prominently around the early evening transition (EET) and stayed at a fairly constant level throughout the night. The physical processes during the EET play a critical role in determining the nocturnal UHI intensity. The near-surface rural temperature inversion strength was a good indicator for nocturnal UHI intensity. As a consequence of the relatively weak near-surface rural inversion, the strongest nocturnal UHI in OKC was less likely to occur in summer. Other meteorological factors (e.g., wind speed and cloud) can affect the stability/depth of the nighttime boundary layer and can thus modulate nocturnal UHI intensity.

Human Excreta as a Stable and Important Source of Atmospheric Ammonia in the Megacity of Shanghai.

Although human excreta as a NH3 source has been recognized globally, this source has never been quantitatively determined in cities, hampering efforts to fully assess the causes of urban air pollution. In the present study, the exhausts of 15 ceiling ducts from collecting septic tanks in 13 buildings with 6 function types were selected to quantify NH3 emission rates in the megacity of Shanghai. As a comparison, the ambient NH3 concentrations across Shanghai were also measured at 13 atmospheric monitoring sites. The concentrations of NH3 in the ceiling ducts ( μg m-3) outweigh those of the open air (~10 μg m-3) by 2–3 orders of magnitude, and there is no significant difference between different seasons. δ15N values of NH3 emitted from two ceiling ducts are also seasonally consistent, suggesting that human excreta may be a stable source of NH3 in urban areas. The NH3 concentration levels were variable and dependent on the different building types and the level of human activity. NH3 emission rates of the six residential buildings (RBNH3) were in agreement with each other. Taking occupation time into account, we confined the range of the average NH3 emission factor for human excreta to be 2–4 times (with the best estimate of 3 times) of the averaged RBNH3 of 66.0±58.9 g NH3 capita-1 yr-1. With this emission factor, the population of ~21 million people living in the urban areas of Shanghai annually emitted approximately 1386 Mg NH3, which corresponds to over 11.4% of the total NH3 emissions in the Shanghai urban areas. The spatial distribution of NH3 emissions from human excreta based on population data was calculated for the city of Shanghai at a high-resolution (100×100 m). Our results demonstrate that human excreta should be included in official ammonia emission inventories.

Selection of Atmospheric Environmental Monitoring Sites based on Geographic Parameters Extraction of GIS and Fuzzy Matter-Element Analysis.

To effectively monitor the atmospheric quality of small-scale areas, it is necessary to optimize the locations of the monitoring sites. This study combined geographic parameters extraction by GIS with fuzzy matter-element analysis. Geographic coordinates were extracted by GIS and transformed into rectangular coordinates. These coordinates were input into the Gaussian plume model to calculate the pollutant concentration at each site. Fuzzy matter-element analysis, which is used to solve incompatible problems, was used to select the locations of sites. The matter element matrices were established according to the concentration parameters. The comprehensive correlation functions KA (xj) and KB (xj), which reflect the degree of correlation among monitoring indices, were solved for each site, and a scatter diagram of the sites was drawn to determine the final positions of the sites based on the functions. The sites could be classified and ultimately selected by the scatter diagram. An actual case was tested, and the results showed that 5 positions can be used for monitoring, and the locations conformed to the technical standard. In the results of this paper, the hierarchical clustering method was used to improve the methods. The sites were classified into 5 types, and 7 locations were selected. Five of the 7 locations were completely identical to the sites determined by fuzzy matter-element analysis. The selections according to these two methods are similar, and these methods can be used in combination. In contrast to traditional methods, this study monitors the isolated point pollutant source within a small range, which can reduce the cost of monitoring.

An attempt at estimating Paris area CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; emissions from atmospheric concentration measurements

Abstract. Atmospheric concentration measurements are used to adjust the daily to monthly budget of fossil fuel CO2 emissions of the Paris urban area from the prior estimates established by the Airparif local air quality agency. Five atmospheric monitoring sites are available, including one at the top of the Eiffel Tower. The atmospheric inversion is based on a Bayesian approach, and relies on an atmospheric transport model with a spatial resolution of 2 km with boundary conditions from a global coarse grid transport model. The inversion adjusts prior knowledge about the anthropogenic and biogenic CO2 fluxes from the Airparif inventory and an ecosystem model, respectively, with corrections at a temporal resolution of 6 h, while keeping the spatial distribution from the emission inventory. These corrections are based on assumptions regarding the temporal autocorrelation of prior emissions uncertainties within the daily cycle, and from day to day. The comparison of the measurements against the atmospheric transport simulation driven by the a priori CO2 surface fluxes shows significant differences upwind of the Paris urban area, which suggests a large and uncertain contribution from distant sources and sinks to the CO2 concentration variability. This contribution advocates that the inversion should aim at minimising model–data misfits in upwind–downwind gradients rather than misfits in mole fractions at individual sites. Another conclusion of the direct model–measurement comparison is that the CO2 variability at the top of the Eiffel Tower is large and poorly represented by the model for most wind speeds and directions. The model's inability to reproduce the CO2 variability at the heart of the city makes such measurements ill-suited for the inversion. This and the need to constrain the budgets for the whole city suggests the assimilation of upwind–downwind mole fraction gradients between sites at the edge of the urban area only. The inversion significantly improves the agreement between measured and modelled concentration gradients. Realistic emissions are retrieved for two 30-day periods and suggest a significant overestimate by the AirParif inventory. Similar inversions over longer periods are necessary for a proper evaluation of the optimised CO2 emissions against independent data.

Influence of monsoons on atmospheric CO2 spatial variability and ground-based monitoring over India

This study examines the role of Asian monsoons on transport and spatial variability of atmospheric CO2 over the Indian subcontinent, using transport modeling tools and available surface observations from two atmospheric CO2 monitoring sites Sinhagad (SNG) and Cape Rama (CRI) in the western part of peninsular India. The regional source contributions to these sites arise from the horizontal flow in conduits within the planetary boundary layer. Greater CO2 variability, greater than 15ppm, is observed during winter, while it is reduced nearly by half during summer. The SNG air sampling site is more susceptible to narrow regional terrestrial fluxes transported from the Indo-Gangetic Plains in January, and to wider upwind marine source regions from the Arabian Sea in July. The Western Ghats mountains appear to play a role in the seasonal variability at SNG by trapping polluted air masses associated with weak monsoonal winds. A Lagrangian back-trajectory analysis further suggests that the horizontal extent of regional sensitivity increases from north to south over the Indian subcontinent in January (Boreal winter).

The application of hierarchical cluster analysis and non-negative matrix factorization to European atmospheric monitoring site classification

The effective classification of atmospheric monitoring sites within a network allows conclusions from measurements to be extrapolated beyond the confines of the site itself and applied to larger areas or populations. This is especially important for the European EMEP ‘supersites’ because these are relatively few in number yet are subject to much investment in composition monitoring capability. Here, the representativeness of the two UK EMEP supersites, Auchencorth and Harwell, was evaluated using the hierarchical cluster analysis (HCA) of all available EMEP monitoring sites based on measured ozone concentration datasets for the period 1991–2010. A novel feature was to apply non-negative matrix factorization (NMF) to order the sites within the HCA dendrograms according to the relative anthropogenic influence on ozone. The ordered dendrograms enabled UK sites to be placed more precisely in a European context. For 2007–2010, all 19 UK EMEP sites were assigned to two of the site classification clusters, with 17 of the sites grouping closely with each other in each cluster. Auchencorth clustered with the sites characterised by less modification of hemispheric background ozone levels, whilst Harwell grouped with the sites showing a more polluted regime. A similar grouping of sites occurred between 1991 and 2010, with relatively closer clustering of Polluted UK sites compared with Remote UK sites due to the larger, transboundary spatial domain for which the Remote UK sites are representative. This tight clustering of the majority of the other UK ozone monitoring sites with either one of the supersites, shows that UK background ozone conditions are well represented by Auchencorth and Harwell, and gives confidence that more extensive chemical climatologies developed for the two supersites will have wider geographical relevance.