Comparison of annular denuder and filter pack collection of HNO3 (g), HNO2((g), SO2 (g), and particulate-phase nitrate,nitrite and sulfate in the south-west desert

During the 15 January–4 February 1986 SCENES Special Study, a comparison study was conducted to determine atmospheric HNO₃ (g), HNO₂ (g), SO₂ (g), and particle-phase nitrate, nitrite and sulfate sampled with annular diffusion denuder and filter pack sampling systems for 12-h periods. The results of the ion chromatographic analyses of the denuder and filter extracts from the annular denuder system showed that an average of 88% of the total nitrate measured was HNO₃ (g), 97% of the total nitrite was HNO₂ (g), and 91% of the total sulfur was present as SO₂ (g). Analyses of the various gas-phase species collected by replicate annular denuder systems indicated that a precision of ± 3% to ± 18% was achieved using these denuders. The good agreement in HNO₃ (g) concentrations observed between the filter pack and the denuder (r²=0.873, slope=1.06±0.03, intercept=0±3.5 nmol m⁻³) results from the fact that the majority of the atmospheric nitrate consisted of HNO₃ (g), which minimized any positive artifact in HNO₃(g) due to loss of HNO₃(g) from particles collected in the filter pack. The particulate-phase nitrate correlation between the two sampling systems was not as good (r²=0.709, slope=0.519±0.045, intercept =0±1.2 nmol m⁻³) because the lower percentage of nitrate present as the particulate species was more affected by the loss of particulate nitrate during sampling with the filter pack.     

Kinetics of evaporation of ammonium chloride and ammonium nitrate aerosols

The evaporation rates of ammonium chloride and ammonium nitrate were measured by continuously and rapidly removing gaseous NH₃ and HNO₃ or HCl from aerosols in an annular denuder. The experiments gave the evaporation rates in terms of mass loss of chloride or nitrate which can be expressed conveniently as the rates of reduction of aerosol radius with time. Both dry aerosols (humidity 30–60% r.h.) and aqueous aerosols (humidity ca 97% r.h.) were studied. Dry aerosols evaporate at rates of −1.05 Å s⁻¹ for NH₄Cl and −0.45Å s⁻¹ for NH₄NO₃, while the evaporation rates of aqueous aerosols expressed as for equivalent dry particles are −4.52 Å s⁻¹ for NH₄Cl and −0.49 Å s⁻¹ for NH₄NO₃. The experimentally measured rates are independent of particle radius and remarkably low compared with those predicted from existing theories of aerosol evaporation, thus implying that there is an unknown kinetic constraint to the achievement of equilibrium at atmospheric temperature and pressures.     

北京中关村地区气溶胶的酸性测量

为了研究大气气溶胶的酸性及其粒径分布,笔者利用自制环状扩散管和三级撞击式组合采样器采样,ｐＨ测量和傅利叶红外光谱技术测量相结合,于１９９４处冬季至１９９５年冬季在北京中关村地区进行了采样分析。结果表明,北京中关村地区气溶胶存在酸性组成,且酸性主要分布于粒径１．５μｍ以下的细粒子中,测得的细粒子最大酸度为５６．６ｎｍｏｌ．ｍ＾－３,各冬季１９９４年冬季和１９９５年夏季气溶胶酸性较强,日平均一般在５ｍ     

Laboratory tests of KI and alkaline annular denuders

Annular denuders coated with KI and with alkaline solutions have been tested for their ability to remove atmospheric pollutants including ozone, NO₂, SO₂, formaldehyde, methyl nitrate and peroxyacetyl nitrate. Tests were carried out at flow rates of 0.4–2.0 ℓ min⁻¹, using particle-free ambient air as well as purified air to study the effect of atmospheric CO₂ on alkaline denuder performance. Denuders coated with KI were efficient in removing O₃, NO₂, SO₂ (> 95%) and PAN (84±3%) but not methyl nitrate (44%) and formaldehyde (<5%). Selective removal of PAN from NO₂, and vice versa, could be obtained with annular denuders coated with NaOH, which removed 100% PAN and ⩽15% NO₂, and with alkaline guaiacol, which removed ⩾99% NO₂ and ⩽6% PAN.     

Measurement and evaluation of acid air pollutants in Chicago using an annular denuder system

The cyclone/annular denuder/filter pack sampling system (ADS) was used to collect and evaluate ambient air pollutants in Chicago. Eighty-one 12-h samples, equally divided into day/night intervals, were collected from April 1990 to March 1991. The chemical species measured were HNO₃, HNO₂, SO₂ and NH₃ in the gas phase, and SO₄²⁻, NO₃⁻, NH₄⁺, and H⁺ in the particulate phase.The ADS data were collected simultaneously with PM10 samples. The particulate matter was analysed for elemental composition. These compositions were combined with the ADS observations and subjected to evaluation using a chemical mass balance receptor model (CMB). From the CMB analysis, the sum of the contributions from soil (15%), mobile (14%), incinerator (2%), coal (0.6%), steel (0.3%) and refinery (0.2%) was 32% of the PM10. NO₃⁻, which was not included in the fingerprints, represented an additional 9% of the PM10. Residual SO₄²⁻ and residual organic carbon, possibly formed in the atmosphere, represented an additional 22 and 20% of the PM10, respectively, leaving only 17% from other unidentified sources. From the standpoint of source contributions of sulfur and nitrogen compounds, coal combustion (23%) and refinery emissions (23%) are the major contributors of ambient sulfur (with 49% from unidentified sources). Mobile sources (87%) contributed most of the ambient nitrogen (with only 2% from unidentified sources).     

Wintertime measurements of aerosol acidity and trace elements in Wuhan,a city in central China

A 2-week intensive ambient aerosol study was conducted in December 1988 in Wuhan (Hubei Province), a city of nearly 2 million located on the Yangtze River in central China (P.R.C.). This is an industrial region where soft coal burning is widespread, and emission controls for vehicles and industrial facilities are minimal. The sampling site was located in one of the civic centers where residential and commercial density is highest. An Andersen dichotomous sampler was operated with Teflon membrane filters to collect fine (d_p < 2.5 μmad) and coarse (2.5 ⩽ d_p < 10 μmad) particles for total mass and element determinations. An annular denuder system (ADS) was used to collect fine fraction aerosols for analyses of ionic species including strong acidity (H⁺).The study was conducted between 18 and 30 December, which was rainless, consistently cool (3–10°C) and overcast, but without fog or acute stagnation. Fine particulate mass (PM, as μ m⁻³) averaged 139 (range 54–207); coarse PM averaged 86 (range 29–179). Trace element concentrations were also high. Crustal elements (Si, Al, Ca and Fe) were found primarily in the coarse fraction, while elements associated with combustion (S, K, Cl, Zn and Se) were enriched in the fine fraction. The concentrations of arsenic and selenium were evidence of a large source of coal burning, while vanadium levels (associated with fuel oil use) were not especially enriched.Despite the seemingly high PM loadings, ionic concentrations were not especially high. The average composition of soluble fine aerosol species (in neq m⁻³) were SO₄²⁻: 520 (range 180–980), NO₃⁻: 225 (range 50–470), Cl⁻: 215 (range 20–640), and NH₄⁺: 760 (range 280–1660). A deficit in accountable FP components (total mass compared to the total of ionic plus element masses) as well as the black appearance of collected materials indicate an abundance of carbonaceous aerosol, as high as 100 μ m⁻³. (total mass compared to the total of ionic plus element masses) as well as the black appearance of collected materials indicate an abundance of carbonaceous aerosol, as high as 100 μ m⁻³Aerosol acidity was negligible during most monitoring periods, H⁺: 14 (range 0–50 neq m⁻³, equivalent to 0–2.5 μm m⁻³ as H₂SO₄). Sulfur dioxide, measured by the West-Gaeke method for part of the study, concentrations were low. Although not directly measured, the aerosol measurments suggested that gaseous HCl (from refuse incineration) and NH₃ (animal wastes) concentrations might have been high. Higher aerosol acidity might be expected if HCl sources were more prominent and not neutralized by local ammonia or other base components.     

Field intercomparison of filter pack and denuder sampling methods for reactive gaseous and particulate pollutants

Atmospheric sulphate, nitrate, chloride and ammonium species have been measured with colocated filter pack and denuder samplers. In general the total amount of a species collected by the two types of sampler was almost the same, although there was evidence of better inlet efficiency for particles in the filter pack sampler. The filter pack gives slightly higher measurements of the volatile species HNO₃, HCl and NH₃ than the denuder, with a corresponding lower measure of particulate NO₃⁻, Cl⁻ and NH₄⁺, attributable to volatilization of ammonium salts from the filter pack pre-filter. In the context of most ambient measurements, the divergences between the techniques are small, and it is argued that differences in these measurement techniques are inevitably site, operator and apparatus-specific and data from one site or research group cannot readily be extrapolated to other sites.     

A denuder technique for the measurement of nitrous acid in urban atmospheres

A new denuder set-up for the measurement of nitrous acid in polluted atmospheres is described here. The set-up is composed of one tetrachloromercurate-coated denuder for the removal of SO₂ and two downstream sodium carbonate-coated denuders for the determination of nitrous acid by the differential technique [Febo et al., 19, 1517–1530 1990]. The removal of SO₂ is necessary in order to avoid the formation of artifact nitrite on the sulfite layer which results from the interaction between atmospheric SO₂ and the Na₂CO₃ coating. Because of this mechanism, the measurement of HONO by means of the previously used NaClNa₂CO₃Na₂CO₃ denuder set-up is heavily biased in all cases when SO₂ and NO₂ are present at high concentration levels (e.g. urban environments).     

Interactions of aerosols (ammonium sulfate,ammonium nitrate and ammonium chloride) and of gases (HCl,HNO3) with fogwater

The concentrations of aerosols (NH₄NO₃, (NH₄)₂SO₄ and NH₄Cl) and of gases (HCl_(g), HNO_3(g), NH_3(g) were determined by denuder methods under different conditions (in the absence of fog, before, during and after fog events). At this site situated in an urban region, high concentrations of the gaseous strong acids HCl_(g) and HNO_3(g) are observed. NH₄Cl and NH₄NO₃ aerosols represent a major fraction of the Cl⁻ and NO₃⁻ aerosols (<2.4 μm)collected by denuders. During a fog event, very high concentrations of SO₄²⁻ were found in small aerosols, which are attributed to the aqueous phase oxidation of SO₂ under the influence of high pH due to the presence of NH₃. Differences in SO₄²⁻ concentrations measured in aerosols (<2.4 μm) and in fog droplets were probably due to mass-transport limitations of the SO₂ oxidation. Ammonium sulfate aerosols represent in some cases a significant fraction of the total S present (SO_2(g) + SO₄²⁻. Soluble aerosols and gases contribute to the composition of fogwater and are released again after fog dissipation.     

Comparison of atmospheric nitrous acid measurements by annular denuder and differential optical absorption systems

As part of the Southern California Air Quality Study (SCAQS), nitrous acid (HONO) measurements were made at Long Beach, CA during the period 11 November–12 December 1987, using two distinctly different techniqes. One of these, the annular denuder method (ADM), used two denuders in tandem, coated with an alkaline medium to obtain 4- or 6-h integrated measurements. A small FEP Tefloncoated glass cyclone preceded the denuders to exclude coarse particles while minimizing loss or artifactual formation of HONO. Nitrite recoveries from the rear denuder were used to correct for sampling artifacts. In the second method, 15 min average HONO concentrations were measured with a differential optical absorption spectrometer (DOAS) coupled to a 25 m basepath, open multiple reflection system operated at a total optical path of 800 m. Period-averaged HONO concentrations from the two techniques were highly correlated (r = 0.94), with DOAS results averaging about 10% higher. However, ADM results were biased high at low HONO concentrations. HONO and NO concentrations showed a significant, positive correlation (r = 0.8), consistent with a common emission source (e.g. auto exhaust) for the two pollutants.     

Origin of soluble chemical species in bulk precipitation collected in Tokyo,Japan: Statistical evaluation of source materials

An iterative least-squares method with a receptor model was applied to the analytical data of the precipitation samples collected at 23 points in the suburban area of Tokyo, and the number and composition of the source materials were determined. Thirty-nine monthly bulk precipitation samples were collected in the spring and summer of 1987 from the hilly and mountainous area of Tokyo and analyzed for Na⁺, K⁺, NH₄⁺, Mg²⁺, Ca²⁺, F⁻, Cl⁻, Br⁻, NO₃⁻ and SO₄²⁻ by atomic absorption spectrometry and ion chromatography. The pH of the samples was also measured. A multivariate ion balance approach (Tsurumi, 1982, Anal. Chim. Acta138, 177–182) showed that the solutes in the precipitation were derived from just three major sources; sea salt, acid substance (a mixture of 53% HNO₃, 39% H₂SO₄ and 8% HCl in equivalent) and CaSO₄. The contributions of each source to the precipitation were calculated for every sampling site. Variations of the contributions with the distance from the coast were also discussed.     

Nitrous and nitric acid measurements at sites in South-East England

Measurements of HONO and HNO₃ have been made using annular denuder samplers at sites in south-east England. Whilst concentrations of HNO₃ exhibited a diurnal variation, with a maximum in mid-afternoon nitrous acid shows the opposite diurnal cycle with maximum levels at night due to daytime photolysis. Concentrations of HONO increase with those of NO₂, and elevated nighttime HONO level appear to be followed by high levels of HNO₃ the following day. Average concentrations of HONO (0.45± 0.26 ppb in 24 h samples are comparable to those of HNO₃ (0.56±0.36 ppb in 24 h samples), each representing about 5–10% of the concentration of NO₂. Although NO₂ oxidation provides the source of HNO₃ concentrations of the two compounds are not related, presumably since the formation of NH₄NO₃ aerosol limits HNO₃ concentrations at out site.     

天津市夏季蜂窝状溶蚀器涂层溶液浓度确定的实验研究

于2013年7月1日～8月31日,在天津市南开大学理化楼楼顶,采用蜂窝状溶蚀器进行了溶蚀器涂层溶液最适浓度的探究实验.结果表明,在天津夏季,蜂窝状溶蚀器的碳酸钠涂层溶液最适浓度为3%,柠檬酸涂层溶液最适浓度为6%.含有溶蚀器系统的颗粒物采样法与传统采样法对比发现,含蜂窝状溶蚀器的采样系统所得到的PM2.5样品浓度有86%低于传统方法所得到的PM2.5样品浓度,其原因主要为1酸/碱性气体被去除,使其无法与富集在采样膜上的颗粒物发生反应,也无法吸附到颗粒物上;2溶蚀器系统采样过程中,部分颗粒物被捕集到溶蚀器上;3酸/碱性气体被去除,导致气-粒平衡被打破,部分颗粒物组分向气态转化.     

应用扩散管测量霾污染期间大气氮硫化合物浓度的方法

活性氮和硫化合物在大气颗粒物形成过程中扮演重要角色,但对它们气相/颗粒相的同步观测结果比较缺乏.本研究尝试基于扩散管的DELTA系统测量氮和硫化合物短时累积浓度,以期捕捉它们在霾污染期间的演变规律.结果表明,DELTA系统收集气态污染物的扩散管中以及颗粒物滤膜上NH_4~+和NO-3空白干扰较小,适用于研究NH_3、HNO_3、NH_4~+和NO-3的日均浓度,可以作为城市环境空气质量监测参数的有效补充;但采样系统中SO_2-4背景含量较高,仅适合监测48 h以上时间尺度的SO_2浓度和周~月尺度SO_2-4浓度,用于大气硫沉降观测.北京2016年5月9日~6月7日观测期间,大气NH_3、HNO_3、NH_4~+和NO-3浓度具有明显的逐日演变规律,呈现出随着风向转变而发生周期性波动的典型特征;这些含氮污染物与PM_(2.5)、CO、SO_2和NO_2浓度的变化规律一致,其来源可能与化石燃料燃烧源有关.污染天NH_3、HNO_3、NH_4~+和NO-3浓度约为清洁天的2倍,但还原性氮和氧化性氮的相态分布在清洁天和污染天无明显差异;整个观测期间,HNO_3/NO-3约为1.2,NH_3/NH_4~+为4.5,春夏之交较高的温度有利于活性氮在气粒平衡过程中偏向于气态形式存在.     

Chemical compositions of PM2.5 aerosol during haze periods in the mountainous city of Yong'an, China

Haze phenomena were found to have an increasing tendency in recent years in Yong'an, a mountainous industrial city located in the center part of Fujian Province, China. Atmospheric fine particles (PM_2.5) in the urban area during haze periods in three seasons (spring, autumn and winter) from 2007 to 2008 were collected, and the mass concentrations and chemical compositions (seventeen elements, water soluble inorganic ions (WSIIs) and carbonaceous species) of PM_2.5 were determined. PM_2.5 mass concentrations did not show a distinct difference among the three seasons. The carbonaceous species organic carbon (OC) and elemental carbon (EC) constituted up to 19.2%-30.4% of the PM_2.5 mass during sampling periods, while WSIIs made up 25.3%-52.5% of the PM_2.5 mass. The major ions in PM_2.5 were SO₄^2-, NO₃^- and NH₄⁺, while the major elements were Si, K, Pb, Zn, Ca and Al. The experimental results (from data based on three haze periods with a 10-day sampling length for each period) showed that the crustal element species was the most abundant component of PM_2.5 in spring, and the secondary ions species (SO₄^2-, NO₃^-, NH₄⁺, etc.) was the most abundant component in PM_2.5 in autumn and winter. This indicated that dust was the primary pollution source for PM_2.5 in spring and combustion and traffic emissions could be the main pollution sources for PM_2.5 in autumn and winter. Generally, coal combustion and traffic emissions were considered to be the most prominent pollution sources for this city on haze days.     

苏州古城区水体污染时空分异特征及污染源解析

利用2012年苏州古城区30个监测断面的11个水质指标数据,综合运用水质指数模型(WQI)、层次聚类(HCA)、后退式判别(DA)、因子分析(FA)、绝对主成分多元线性回归(APCS-MLR)及GIS平台系统分析了旅游城市苏州古城区河网水体污染物时空分异特征及污染源解析.结果表明:①苏州古城区内城河及外围河道水体的CCME WQI值介于40~74之间,其中,66.67%的监测点水环境遭到严重破坏,主要集中在内城河河道;②系统聚类分析将采样时间分为1—3月、11月及4—6月、7—10月3个时段;将采样点分为2类,从空间上反映了古城区内城河与外围河道的污染程度;③采样时间和采样点聚类分析结果的判别分析交叉验证,正确率分别达到88.1%和78.5%;表征时间差异性用了7个指标,分别为总氮(TN)、总磷(TP)、溶解氧(DO)、水温(T)、高锰酸盐指数(COD Mn)、藻密度(Algae density)、叶绿素(Chl),表征空间差异性用了5个指标,分别为总氮(TN)、氨氮(NH3-N)、溶解氧(DO)、浊度(Turb)、水温(T);显著性指标的时空差异性比较明显;④古城区内城河河道在1—3月、11月及4—6月、7—10月3个时段内的因子分析分别提取4、3和4个因子,累积解释方差分别为83.64%、72.67%和77.98%;古城区外围河道在全年内的因子分析提取了3个因子,累积解释了62.28%的总方差;因子分析表明,古城区内城河及外围河道主要为氮、磷等营养物质污染及夏季藻类爆发的问题,与古城区外围河道相比内城河河道的污染更为严重,应优先开展治理;内城河氮、磷污染除了有来自生活、餐饮旅游等第三产业的污染外,还受到降雨地表径流及河道底泥释放的非点源污染影响;⑤绝对主成分多元线性回归(APCS-MLR)表明,总氮(TN)、氨氮(NH3-N)、总磷(TP)和高锰酸盐指数(COD Mn)主要来自城市生活及餐饮旅游等第三产业污水.研究结果可为苏州古城区河道水环境改善治理提供参考.     

Fluxes of nitric and nitrous oxides from agricultural soils in a cool temperate climate

Fluxes of NO and N₂O from sandy loam soils cropped with winter wheat and a clay loam soil under ryegrass, with and without the addition of NH₄NO₃ fertilizer, were measured using static and dynamic chamber methods. Nitric oxide fluxes ranged from −0.3 (deposition) to 6.9 (emission) ng NO-N m⁻² s⁻¹. The corresponding N₂O flux ranged from 0 to 91 (emission) ng N₂O-N m⁻² s⁻¹. The NO flux was temperature dependent. Activation energies ranged from 40 to 81 kJ mol⁻¹. Nitric oxide and N₂O fluxes increased linearly with soil available nitrogen (NH₄ + NO₃). Emissions of NO and N₂O were not detectable from unfertilized ryegrass plots. Instead, nitric oxide was absorbed by the soil and vegetation at a maximum rate of 0.31 ng NO-N m⁻² s⁻¹. The aeration state of the soil controlled the relative rates of NO and N₂O emission. Nitric oxide was the major gas emitted from well aerated soils, conditions that favour nitrification. The NO/N₂O emission ratio was >100 for the coarse-textured sandy loam soil and the clay loam soil only during low rainfall periods. Nitrous oxide was the major gas emitted from less aerated soils, conditions that allowed denitrification to occur. The NO/N₂O emission ratio was <0.001 for the clay loam soil when rainfall was high and soils were wet. Extrapolation to the U.K. situation showed that agricultural land may account for 2–6% of the total annual NO_x emission and for 16–64% of the total annual N₂O emission in the U.K.     

Microbial community characterization, activity analysis and purifying efficiency in a biofilter process

The growth and metabolism of microbial communities on biologically activated carbon(BAC) play a crucial role in the purification of drinking water.To gain insight into the growth and metabolic characteristics of microbial communities and the efficiency of drinking water treatment in a BAC filter,we analyzed the heterotrophic plate count(HPC),phospholipid,dehydrogenase,metabolic function and water quality parameters during start-up and steady-state periods.In the start-up process of the filter with natural biofilm colonization,the variation in heterotrophic plate count levels was S-curved.The total phospholipid level was very low during the first 5 days and reached a maximum value after 40 days in the filter.The activity of dehydrogenase gradually increased during the first 30 days and then reached a plateau.The functional diversity of the microbial community in the filter increased,and then reached a relatively stable level by day 40.After an initial decrease,which was followed by an increase,the removal rate of NH4+-N and COD Mn became stable and was 80% and 28%,respectively,by day 40.The consumption rate of dissolved oxygen reached a steady level after 29 days,and remained at 18%.At the steady operation state,the levels of HPC,phospholipid,dehydrogenase activity and carbon source utilization had no significant differences after 6 months compared to levels measured on day 40.The filter was shown to be effective in removing NH4+-N,NO2--N,COD Mn,UV 254,biodegradable dissolved organic carbon and trace organic pollutants from the influent.Our results suggest that understanding changes in the growth and metabolism of microorganisms in BAC filter could help to improve the efficiency of biological treatment of drinking water.     

三峡水库蓄水后不同水位期干流氮、磷时空分异特征

研究三峡水库蓄水前后营养盐的变化,对于探讨水库运行对其的影响并提出合理的管理建议具有重要意义.依据2008年3月～2009年2月对长江干流三峡区段朱沱、寸滩、扇沱、清溪场、晒网坝、培石,共6个断面和其中1个垂直断面逐月水文、水质监测,按照三峡水库运行的水位特点,将数据样本分成高水位(10～2月)和低水位(3～9月)2个...     

A comparison of major chemical species seasonal concentration and accumulation at the South Pole and summit,Greenland

High-resolution snow chemistry records have been recovered from a site close to the South Pole, covering the period 1955–1989, and from Summit, Greenland, for the periods 1979–1987 and 1259–1989. The seasonal variation of the major ions relative to δ¹⁸O and their average yearly fluxes are compared for the two sites. Comparisons are also made to limited available aerosol data. Gaseous species and some species with gaseous precursors (NO₃, NH₄ and excess Cl) have similar timings in South Pole and pre-1900 Summit snow. Timing of non-sea-salt (nss) SO₄ and species that are generated as marine and crustal aerosols (Na, nss Mg and nss Ca) differ between the two sites. The timing of nss SO₄ and NO₃ is complicated in recent precipitation at Summit, Greenland, by the impact of anthropogenic emissions. Fluxes of sea-salt species, nss SO₄ and NO₃ (pre-11900 values for Summit) are less than a factor of 2 higher at Summit. Species with a continental source: nss K, nss Mg, nss Ca and NH₄ are more than five-fold higher at Summit.