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).     

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.     

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 continuous-flow denuder for the measurement of ambient concentrations and surface-exchange fluxes of ammonia

A new diffusion denuder is described for the continuous measurement of atmospheric ammonia. Ammonia is collected in an absorption solution in a rotating denuder, separated from interfering compounds by diffusion through a semi-permeable membrane and detected by conductometry. The method is free from interferences by other atmospheric gases, with the exception of volatile amines. The detection limit is 6 ng m⁻³ for a 30-min integration time. This compact instrument is fully automated and suited for routine deployment in field studies. The precision is sufficiently high for micrometeorological studies of air-surface exchange of ammonia.     

A multiple-system,multi-channel diffusion denuder sampler for the determination of fine-particulate organic material in the atmosphere

Measurement of the loss of semi-volatile organic compounds from particles collected with a filter is carried out by comparing the amounts collected by comparable filter pack and diffusion denuder samplers. The sorbents used to collect organic compounds in the denuder and sorbent filters must have the same efficiency for collection of all gas-phase organic compounds present. Interpretation of the data requires that the efficiency of collection of gas-phase compounds by the denuder be known. In theory this can be accomplished by determination of the deposition pattern of all organic compounds collected in the denuder, but in practice this is very difficult if the organic material consists of a wide variety of compounds. An alternative approach is to determine the breakthrough of organic compounds in a sampler with a particle-collection filter preceding the denuder and sorbent filter. In such a sampler only gas-phase organic material enters the denuder. We have developed both a multi-channel parallel plate diffusion denuder sampler and a comparable sampler in which the denuder is preceded by a filter. Samples can be collected with the multisystem sampler at a flow rate of 35 sLpm. The denuder surfaces and the sorbent filters are made from sheets of an activated charcoal-impregnated filter paper. Collection of semi-volatile compounds by the samplers has been characterized and the systems have been field tested. The samplers are now being used for the routine collection and determination of semi-volatile organic compounds in particles at Canyonlands National Park in southeastern Utah. Available data from this field program show significant losses of particulate organic compounds on a quartz filter due to volatilization during sampling.     

Determination of aerosol strong acidity losses due to interactions of collected particles: Results from laboratory and field studies

Existing methods of measuring atmospheric aerosol strong acidity adequately prevent neutralization of fine-particle acidity by removing course alkaline particles and gaseous ammonia from air samples. However, these techniques do not consider particle interactions on the collection medium; therefore, they may still underestimate the actual aerosol acidity. Assessment of acid neutralization due to such interactions is made possible using annular denuder technology in conjuction with a newly designed filter pack. The amount of sulfate-related acidity neutralized by the collected ammonium nitrate (and possibly ammonium chloride and organic acid ammonium salts) is determined. Laboratory data suggest that large fractions of sulfate-related aerosol acidity are neutralized by ammonium nitrate particles during collection on filter media. Field data from the Harvard Acid Aerosol Health Effects Study also suggest that ammonium nitrate and possibly other ammonium salts, such as ammonium chloride, neutralize collected acid aerosols. For low-acid aerosol concentrations, the correction factor is significant; whereas, for high-acid concentrations, correction is negligible.     

Nitrogenous air pollutants at a southern California mountain forest smog receptor site

Ambient levels of the nitrogenous pollutants NO, NO₂, nitric acid, nitrous acid, ammonia, particulate nitrate, particulate ammonium, peroxyacetyl nitrate (PAN) and peroxypropionyl nitrate (PPN) have been measured at a southern California mountain forest location severely impacted by urban photochemical smog. Air quality at the mountain forest location was characterized by high levels of nitric acid (up to 18 ppb) and the phytotoxic peroxyacyl nitrates PAN (up to 22 ppb) and PPN (up to 5 ppb). Alkyl nitrates were below our detection limits of 0.05–0.5 ppb. The (PAN + PPN)/NO₂ ratios varied substantially (range 0.03–2.27) and were generally large, with typical 24-h averages of 0.19–0.50. Diurnal variations of the (PAN/PPN)/NO₂ ratio exhibited both nighttime and daytime maxima reflecting diurnal variations in PAN (and PPN) thermal stability and photochemical production rates, respectively. Organic nitrogen-containing oxidation products (PAN + PPN) were more abundant than inorganic nitrate (HNO₃ + NO₃⁻), with an average organic/inorganic concentration ratio of 2.5 (daytime ratio 1.0; nighttime ratio 3.7). The four oxidation products PAN, PPN, HNO₃ and NO₃⁻ together accounted for 0.26 of the total reactive nitrogen. The results are discussed with respect to diurnal and seasonal variations and in terms of NO₂ atmospheric oxidation pathways. Deposition fluxes and velocities to ponderosa pine have been measured for inorganic nitrate and for ammonium and have been compared with those obtained at other mountain forest locations.     

天津市冬季蜂窝状溶蚀器涂层溶液最适浓度研究

在特定时间特定地点利用溶蚀器PM2.5采样系统进行PM2.5采样前,应首先确定溶蚀器涂层溶液最适浓度.为确定在天津市冬季利用蜂窝状溶蚀器PM2.5采样系统采样的最优化条件,于2014年1月1日~2月24日,在南开大学理化楼楼顶进行蜂窝状溶蚀器涂层溶液最适浓度的条件实验.结果表明:在天津地区冬季, 蜂窝状溶蚀器的碳酸钠涂层溶液最适浓度为4%,柠檬酸涂层溶液最适浓度为5%; 环境空气中HCl气体对PM2.5中Cl-的质量浓度测定影响不大,而HNO3、SO2、NH3等酸/碱性气体对PM2.5中相对应离子的质量浓度测定影响较大.     

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.     

两广地区硝酸和硝酸盐湿去除研究

1986至1988年在我国两广地区进行了三年的春季降水集中观测,根据所测得的大气硝酸、硝酸盐气溶胶和雨水硝酸盐浓度,计算了硝酸和硝酸盐的清除比,其平均值分别为1.7×106和5.6×105。利用连续降雨样品的硝酸盐沉降量计算了硝酸盐的清除系数λ,λ值约在10-4-10-5S-1之间。      

极谱催化波法测定痕量亚硝酸根的研究

在含稀硫氰酸盐的底液中 ,在单扫示波极谱仪上 ,有一灵敏的亚硝酸根催化波。峰电位为 -0 .47V( vs·SCE)。阳极化二阶导数峰高与亚硝酸根浓度在 1× 10 - 7～ 5× 10 - 5mol/L 之间成线性关系。检测限达 5× 10 - 5mol/L( 2 .3ppbNO - 2 )。试验了多种共存离子对测定的影响 ,表明该法具有较好的选择性 ,尤其是大量硝酸根不干扰。应用该法测定了许多样品中的亚硝酸根 ,并对该波的机理进行了研究 ,结果证明该波是 [SCN· NO]催化溶液中的溶解氧还原所致     

化学氮肥对蔬菜硝酸盐污染影响的研究

蔬菜是一种容易富集硝酸盐的作物,菜农为了获得高产,而超量施用化学氮肥,致使蔬菜硝酸盐累积量剧增,品质恶化。研究表明：筛选出氯化铵和硫酸铵两种氮肥;施氮剂量每hm²以200kg为临界值;施氮安全始期,以追氮后8天上市为宜;化学氮肥与厩肥、土杂肥配用,能有效控制和降低蔬菜硝酸盐的累积分别达67.4％和45.7％。硝酸盐是亚硝胺的前体物,应减轻其对人体健康的潜在危害,并提高蔬菜品质。     

Varying water column stability controls the denitrification process in a subtropical reservoir, Southwest China

Reservoirs are regarded as hotspots of nitrogen transformation and potential sources of nitrous oxide（N₂O）. However, it remains unclear how the hydrological conditions due to dam construction control the processes of nitrogen transformation in reservoir waters. To address this issue, we examined the spatial-temporal characteristics of nitrate concentrations, δ¹⁵N-NO₃^-, δ¹⁸O-NO₃^-, δ¹⁸O-H₂O, relative...     

离子色谱同时测定脱硫脱硝副产物中SO_3~(2-)、SO_4~(2-)、NO_2~-、NO_3~-方法研究

使用离子色谱测脱硫脱硝副产物中的亚硫酸根、硫酸根、亚硝酸根、硝酸根4种离子,研究通过加甲醛抑制亚硫酸根的氧化,研究甲醛对4种离子,以及4种离子之间在测定时是否会相互影响。结果发现:硫酸根、亚硝酸根、硝酸根3种离子比较稳定,而SO_3~(2-)易被氧化。发现采用甲醛作为抗氧化剂可以较好地抑制SO_3~(2-)的氧化;用1 mmol/L的KOH作为淋洗液时,甲醛的质量分数可选为0.05%,若甲醛浓度过高,除影响色谱柱寿命外,SO_3~(2-)的出峰面积也会变小。甲醛的加入不影响亚硝酸根和硝酸根的出峰。亚硫酸根、硫酸根、亚硝酸根、硝酸根同时测定过程中相互干扰不大,4种离子的线性关系较好。采用甲醛做抗氧化剂时,不应采用Na_2CO_3等弱碱溶液作为淋洗液。总之,通过加入适量的甲醛,离子色谱法可以准确同时测定脱硫脱硝产物的亚硫酸根、硫酸根、亚硝酸根、硝酸根4种离子。     

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.     

河口区域反硝化作用研究进展

反硝化作用是河口区域去除NO-3的重要途径.其产物之一N2O是一种温室效应很强的温室气体.本文综述了河口区域反硝化作用在N元素生物地球化学循环过程中的重要作用,概述了不同测定反硝化速率的方法,并提出了各种方法的优缺点.总结了反硝化作用的影响因素:O2浓度,NO3-,有机质,温度,生物等.在这些因素的影响下,反硝化存在着区域性,季节性以及昼夜性差异.最后,提出了目前研究中存在的不足及发展方向.     

扩散管在大气汞分析中的应用

本文叙述一种分离大气中气态汞和颗粒态汞的扩散管采样方法 ,将它与传统的滤膜过滤法测得的结果进行比较。当使用 6 0 0 mm长的扩散管 ,采样流速为 1L· m in-1时 ,它对气态汞的采样效率可达 99%以上     

Review of heterogeneous photochemical reactions of NOy on aerosol－A possible daytime source of nitrous acid (HONO) in the atmosphere

As an important precursor of hydroxyl radical, nitrous acid (HONO) plays a key role in the chemistry of the lower atmosphere. Recent atmospheric measurements and model calculations show strong enhancement for HONO formation during daytime, while they are inconsistent with the known sources in the atmosphere, suggesting that current models are lacking important sources for HONO. In this article, heterogeneous photochemical reactions of nitric acid/nitrate anion and nitrogen oxide on various aerosols were reviewed and their potential contribution to HONO formation was also discussed. It is demonstrated that HONO can be formed by photochemical reaction on surfaces with deposited HNO3 , by photocatalytic reaction of NO2 on TiO2 or TiO2 -containing materials, and by photochemical reaction of NO2 on soot, humic acids or other photosensitized organic surfaces. Although significant uncertainties still exist in the exact mechanisms and the yield of HONO, these additional sources might explain daytime observations in the atmosphere.     

Greenhouse gas abatement strategies for animal husbandry

Agriculture contributes significantly to the anthropogenic emissions of non-CO₂ greenhouse gases methane and nitrous oxide. In this paper, a review is presented of the agriculture related sources of methane and nitrous oxide, and of the main strategies for mitigation. The rumen is the most important source of methane production, especially in cattle husbandry. Less, but still substantial, amounts of methane are produced from cattle manures. In pig and poultry husbandry, most methane originates from manures. The main sources of nitrous oxide are: nitrogen fertilisers, land applied animal manure, and urine deposited by grazing animals. Most effective mitigation strategies for methane comprise a source approach, i.e. changing animals’ diets towards greater efficiencies. Methane emissions, however, can also be effectively reduced by optimal use of the gas produced from manures, e.g. for energy production. Frequent and complete manure removal from animal housing, combined with on-farm biogas production is an example of an integrated on-farm solution. Reduced fertiliser nitrogen input, optimal fertiliser form, adding nitrification inhibitors, land drainage management, and reduced land compaction by restricted grazing are the best ways to mitigate nitrous oxide emissions from farm land, whereas, management of bedding material and solid manure reduce nitrous oxide emissions from housing and storage. Other than for methane, mitigation measures for nitrous oxide interact with other important environmental issues, like reduction of nitrate leaching and ammonia emission. Mitigation strategies for reduction of the greenhouse gases should also minimize pollution swapping.     

土壤氮素的转化过程中温室效应气体的释放和吸收

一氧化二氮(NO₂)是一个重要的温室效应气体,一氧化氮(NO)对温室效应的产生也有间接的作用。土壤作为这两种气体的主要来源的重要性引起了人们的广泛重视。本文主要讨论了土壤中的氮素生物转化过程与NO₂和NO的产生和再利用。以及影响土壤中温室效应气体的释放和吸收的环境条件。