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 comparison of measurements of atmospheric ammonia by filter packs,transition-flow reactors,simple and annular denuders and fourier transform infrared spectroscopy

Using data obtained during the 1985 Nitrogen Species Methods Comparison Study (1988,Atmospheric Environment22, 1517), several measurement methods for sampling ambient NH₃ are compared. Eight days of continuous measurements at Pomona College, a smog receptor site in Los Angeles, provided an extensive data base for comparing the following methods: Fourier transform i.r. spectroscopy (FTIR), three filter pack configurations, a simple and an annular denuder, and the transition flow reactor. FTIR was defined as the reference method and it reported hourly NH₃ concentrations ranging from > 60 to 2280 nmol m⁻³ (1.5−57ppb) during the course of the study, the highest values coming from the influence of nearby livestock operations.Although only limited quality assurance procedures were carried out, the following conclusions can, nevertheless, be drawn: most of the methods correlated highly with the FTIR method (correlation coefficientr > 0.96); generally, the linear regression slopes were close to unity and the intercepts were insignificantly different from zero at the 95% confidence level); relative to the FTIR average values, (1) for 4–6 h sampling periods, the averages of the three filter packs from three research groups were 83–130% and the annular denuder average was 87%, and (2) for 10–12 h sampling periods, the simple denuder averaged 90% and the two transition flow reactors were 77–98%. Possible reasons for the reported systematic biases are presented, but these are not able to fully explain the large range of differences reported by the various methods.     

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).     

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.     

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.     

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.     

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.     

Formation of HNO2 on aerosol surfaces during foggy periods in the presence of NO and NO2

A commercial Differential Optical Absorption Spectrometer (DOAS), measuring trace gases absorbing in the u.v./vis region was used for obtaining information on aerosol parameters (e.g. total surface) based on the observed Mie scattering. This procedure allows simultaneous measurements of trace gas concentrations and aerosol parameters within the same air volume. A series of measurements of HNO₂, NO₂, NO, SO₂ and aerosol parameters was performed at Ispra in northern Italy. The observations show a rapid formation of gaseous HNO₂ during foggy episodes and give direct evidence of an important contribution of reactions on wet aerosols to the transformation of tropospheric NO_x into HNO₂.     

Measurements of atmospheric HNO3, HCl and associated species on a small network in eastern England

Measurements of gaseous HNO₃, HCl and NH₃ and particulate NO₃⁻, SO₄²⁻, Cl⁻ and NH₄⁺ have been made at a small network of sites in eastern England using sampling intervals from 3 h to 7 days. Both HCl and HNO₃ are spatially rather uniform, with some variation apparently due to spatial variations in NH₃, which stoichiometrically exeeded the sum of both gaseous acids. Mean concentrations of NH₃, HCl and HNO₃ between February 1987 and January 1988 were 1.90, 0.67 and 1.01 μg m⁻³, respectively. Pollution roses revealed low NH₃ concentrations, and high associated HCl and HNO₃ with winds from the North Sea. HCl, but not HNO₃ showed an appreciable elevation in concentration on the sector NW from our site, which we speculate may be due to the large capacity of coal-fired power stations in this upwind sector. Three-hourly data have been examined for diurnal effects and its is concluded that nocturnal formation of NO₃⁻ is occurring.     

Observations of N2O5 and NO3 at a suburban environment in Yangtze river delta in China: Estimating heterogeneous N2O5 uptake coefficients

The nitrate radical (NO₃) and dinitrogen pentoxide (N₂O₅) play an important role in the nocturnal atmosphere chemistry. Observations of NO₃ radicals and N₂O₅ were performed in a semirural ground site at Tai'Zhou in polluted southern China using cavity ring down spectroscopy (CRDS) from 23 May to 15 June 2018. The observed NO₃ and N₂O₅ concentrations were relatively low, with 1 min average value of 4.4 ± 2.2 and 26.0 ± 35.7 pptV, respectively. The N₂O₅ uptake coefficient was determined to be from 0.027 to 0.107 based on steady state lifetime method. Fast N₂O₅ hydrolysis was the largest contributor to the loss of NO₃ and contributed to substantial nitrate formation, with an average value of 14.83 ± 6.01 µg/m³. Further analysis shows that the N₂O₅ heterogeneous reactions dominated the nocturnal NO_x loss and the nocturnal NO_x loss rate is 0.14 ± 0.02 over this region.     

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.     

Characterization of atrazine degradation and nitrate reduction by Pseudomonas sp. strain ADP

Concomitant atrazine degradation and nitrate reduction by a pure culture of Pseudomonas sp. strain ADP were studied. Under anoxic conditions, Ps ADP grew well and degraded atrazine efficiently in the presence of nitrate. Similar atrazine degradation rates were observed under both anoxic and aerobic conditions: 30.7±2.83 and 36.2±0.44 mg atrazine g⁻¹ cell h⁻¹, respectively. A high denitrification rate of 90.8±8.22 mg NO₃⁻-N g⁻¹ cell h⁻¹ was also observed using Ps ADP with citrate as the electron donor. The required citrate to nitrate ratio for complete denitrification was 5.11±0.15 g citrate g⁻¹ NO₃⁻-N.     

Observed levels and trends of gaseous SO2 and HNO3 at Mt. Waliguan, China: Results from 1997 to 2009

Long-term measurements of SO2 and HNO3,particularly those from the background sites,are rarely reported.We present for the first time the long-term measurements of SO2 and HNO3 at Waliguan(WLG),the only global baseline station in the back-land of the Eurasian Continent.The concentrations of SO2 and HNO3 were observed at WLG from 1997 to 2009.The observed annual mean concentrations of SO2 and HNO3 at WLG were 1.28±0.41 and 0.22±0.19μg/m3,respectively.The HNO3 concentrations were much higher in warmer seasons than in colder seasons,while the SO2 concentrations showed a nearly reversed seasonal pattern.In most months,the concentration of HNO3 was significantly correlated with that of SO2,suggesting that some common factors influence the variations of both gases and the precursors of HNO3 may partially be from the SO2-emitting sources.The SO2 concentration had a very significant(P < 0.0001) decreasing trend(-0.2μg/(m3·yr)) in 1997-2002,but a significant(P < 0.05) increasing trend(+0.06 μg/(m 3 ·yr)) in 2003-2009.The HNO3 concentration showed no statistically significant trend during 1997-2009.While the decrease of SO2 in 1997-2002 agrees with the trend of global SO2 emissions,the increase in 2003-2009 is not consistent with the decreasing trends in many other regions over the world.Trajectory analysis suggests that the airmasses from the northern Qinghai-Tibetan Plateau and the Takla Makan Desert regions contributed significantly to the increasing trends of SO2 and HNO3 at WLG in 2003-2009,with a rate of +0.13μg/(m3·yr) and +0.007μg/(m3·yr),respectively.     

The removal of nitric acid to atmospheric particles during a wintertime field study

A field was conducted in Warren, MI, during the 1987/88 winter period to examined the reaction of HNO₃ with particulate salt from road deicing. Samples of gases and particles were collected on a daily basis over a 4-month period. If HNO₃ reacts with particulate salt, particles of sodium nitrate will be formed and gaseous hydrochloric acid will be released. Thus, during the periods of high salt concentrations, one would expect increases in HCl and particulate NO₃⁻ and a decrease in HNO₃. The effect was observed, although the total amount of NaNO₃ formed was not large. The increase in particulate NO₃⁻ did not appear in the large particle mode. Although more than 40% of the salt was present as very large particles (> 8 μm), most of the surface area was associated with small particles. Since the reaction occurred at the particle surface, the NO₃⁻ appeared in the small particle mode. Large-particle nitrate has been observed in association with sea salt and crustal particles and has also been attributed to reactions with HNO₃. These cases will be reconsidered based on the road salt results.     

不同酸性气体及相对湿度对海盐氯损耗过程的影响

使用在广州南村站、深圳竹子林站及西涌站的MARGA仪器实测资料,分析了不同酸性气体及相对湿度对海盐氯损耗过程的影响.在分析深圳竹子林站、西涌站的海盐氯损耗中发现,竹子林站氯损耗平均为48.0％,西涌站海盐氯损耗平均为56.9％,氯损耗的峰值一般出现于下午14时.西涌站、竹子林站和广州南村站酸性气体和碱性气体均以HNO2、SO2、NH3为主,但各站点的比例分布不同,西涌站以HNO2最多(42％),SO2(32％)次之;竹子林站以NH3与SO2为主,百分比分别为36％和34％;广州南村站以SO2为主(58％),NH3次之(20％);而三站HNO3所占比例很小,均为7％.另外,分析了HCl的来源,主要关注了海盐粒子中的NaCl与HNO3反应、NH4Cl的挥发及H2SO4与NaCl的反应这3个来源,发现西涌站与竹子林站HCl和HNO3之间的线性关系较好(R2西涌=0.689,R2竹子林=0.594),说明西涌站与竹子林站的HCl主要来源于NaCl与HNO3反应过程中Cl被HNO3置换而成;而广州南村站二者线性关系较差(R2南村=0.295),说明还存在其他的损耗机制.在研究相对湿度对氯损耗的影响中发现,相对湿度低时氯损耗更容易发生.     

Nitrate formation on sea-salt and mineral particles—A single particle approach

Heterogeneous reactions of NO₂ and HNO₃ at sub-ppm levels with individual sea-salt and mineral particles were investigated. Particles deposited on filters and on electron microscope grids placed in a Teflon reaction chamber, were exposed to NO₂ or HNO₃ under controlled conditions. Experiments were carried out under dark conditions and were repeated under u.v. radiation (solar simulation). Nitrates formed on the particles were determined by bulk and individual particle analyses. Individual sea-salt and mineral particles were observed in a transmission electron microscope for the presence of nitrate on the particle surface.The formation of nitrates on sea-salt particles under dark conditions, was in the range of 0.1–3.3 mg NO₃⁻ g⁻¹ NaCl. Higher values were obtained for mineral particles: 0.2–8.2 mg NO₃⁻ g⁻¹ aerosol ([NO₂] =0.18 and 0.54 ppm; [HNO₃] = 0.04 ppm; exposure time 1–7 days; relative humidity = 70%). The formation of nitrates on sea-salt particles increased from 3.0 to 16.1 mg NO₃⁻ g⁻ NaCl when u.v. radiation was added. Mineral particles did not show a significant increase in nitrate formation under u.v. radiation.Microscopy showed that about 50% of the soil particles reacted with NO₂ and HNO₃ to form mixed nitrate particles. Almost all sea-salt particles (above 95%) reacted with both gases, although the reaction was not complete and took place only on the particle surface.Application of electron microscopy and a specific microspot technique provided direct evidence for the formation of nitrate on sea-salt and mineral particles exposed to NO₂ and HNO₃.     

Root- and peat-based CO2 emissions from oil palm plantations

Measured carbon dioxide (CO₂) flux from peat soils using the closed chamber technique combines root-related (autotrophic + heterotrophic where rhizosphere organisms are involved) and peat-based (heterotrophic) respiration. The latter contributes to peat loss while the former is linked to recent CO₂ removal through photosynthesis. The objective of this study was to separate root- from peat-based respiration. The study was conducted on peatland under 6 and 15 year old oil palm (Elaeis guineensis Jacq.) plantations in Jambi Province, Indonesia in 2011 to 2012. CO₂ emissions were measured in the field from 25 cm diameter and 25 cm tall closed chambers using an infrared gas analyser. Root sampling and CO₂ emissions measurements were at distances of 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, and 4.5 m from the centre of the base of the palm tree. The emission rate for the six and 15 year old oil palm plantations at ≥3.0 m from the centre of the tree were 38.2?±?9.5 and 34.1?±?15.9 Mg CO₂ ha^?1 yr^?1, respectively. At distances <2.5 m, total respiration linearly decreased with distances from the trees. Heterotrophic respirations were 86 % of the 44.7?±?11.2 and 71 % of 47.8?±?21.3 Mg CO₂ ha^?1 yr^?1 of weighted surface flux, respectively for the 6 and 15 year old plantations. We propose that CO₂ flux measurements in oil palm plantations made at a distance of ≥3 m from the tree centre be used to represent the heterotrophic respiration that is relevant for the environmental impact assessment.     

多介质土壤滤层系统(MSL)与潜流式人工湿地技术处理海水养殖废水的效能比较

为探索经济可行的海水养殖废水处理技术,选取南美白对虾海水养殖废水,对比研究了多介质土壤滤层(multi-soillayer,MSL)系统和4种不同植物配置潜流式人工湿地(大米草型、芦苇型、香蒲型和无植物型)在400 L·(m2·d)-1水力负荷下的废水处理效果.结果表明,MSL对化学需氧量(COD)、总磷(TP)、总氮(TN)、氨氮(NH+4-N)和硝态氮(NO-3-N)的平均去除率分别为80.38%±2.14%、68.14%±3.51%、40.79%±3.10%、42.68%±2.90%和54.19%±5.15%,均高于其他4种不同植物配置的潜流式人工湿地的处理效果.4种人工湿地系统对各污染物的去除率从高到低依次为:大米草型>芦苇型>香蒲型>无植物型.     

峨眉山地区大气中的硝酸和氨

为了研究峨眉山地区降水、云雾水明显酸化的原因,1985年10月我们进行了集中观测,并就其测定结果进行分析研究。     

A comparison of calibration and measurement techniques for gas chromatographic determination of atmospheric peroxyacetyl nitrate (PAN)

A 24 day intercomparison study of peroxyacetyl nitrate (PAN) measurement was conducted in Egbert, Ontario, in February–March 1989. Two GC/ECD systems and one GC using a luminolchemiluminescence based detection device were involved. To separate the influence of calibration errors vs possible chromatographic interferences, a series of laboratory standards (gaseous PAN concentrations determined by either i.r. or by chemiluminescence) were exchanged. For all three GCs the results of analysis of standard samples were within ±25% of the standard concentration. For ambient air PAN measurements (concentrations ranging from 0.15 to 2 ppb), plots of each set of measurement data regressed against those of the other two techniques were obtained. Linear regression of the data from ambient air analysis for the two GC/ECD systems yielded a slope and intercept of 1.14±0.01 and −0.03±0.05, respectively (r = 0.995). The plot of the Luminol-based GC against the AES GC/ECD yielded a slope of 1.08±0.03 and an intercept of 0.08±0.24 (r = 0.864). The results demonstrated the reliability of the chemiluminescence calibration technique, and indicated that the luminol-based PAN measurement device can yield accurate and sensitive measurements of ambient PAN concentrations.