北京大气中NO、NO2和O3浓度变化的相关性分析

臭氧（O₃）是城市污染大气中的首要光化学污染物,其变化规律与氮氧化物(NO_x=NO+NO₂)关系密切.采用49C臭氧分析仪和42CTL氮氧化物分析仪对北京城区O₃和NO_x浓度进行了连续观测,时间为2004-08～2005-07.结果显示,O₃和OX（O₃+NO₂）浓度在午后15:00左右出现峰值,NO_x呈双峰态日变化,在07:00和23:00左右出现峰值.不同季节污染物的浓度变化存在差异,O₃和NO_x浓度分别在夏季和冬季达到最大.NO_x浓度存在100×10^-9(体积分数)的“分界点”,NO_x低浓度时以NO₂为主,NO_x高浓度时NO占大部分.OX区域贡献和局地贡献存在明显的季节变化,前者主要受区域背景O₃的影响,在春季最大,后者主要受局地NO_x光化学反应的制约,在夏季最强,同时OX组分呈现显著的昼夜差异.     

Measurement of heterogeneous uptake of NO2 on inorganic particles, sea water and urban grime

Heterogeneous reactions of NO₂ on different surfaces play an important role in atmospheric NO_x removal and HONO formation, having profound impacts on photochemistry in polluted urban areas. Previous studies have suggested that the NO₂ uptake on the ground or aerosol surfaces could be a dominant source for elevated HONO during the daytime. However, the uptake behavior of NO₂ varies with different surfaces, and different uptake coefficients were used or derived in different studies. To obtain a more holistic picture of heterogeneous NO₂ uptake on different surfaces, a series of laboratory experiments using different flow tube reactors was conducted, and the NO₂ uptake coefficients (γ) were determined on inorganic particles, sea water and urban grime. The results showed that heterogeneous reactions on those surfaces were generally weak in dark conditions, with the measured γ varied from <10^?8 to 3.2 × 10^?7 under different humidity. A photo-enhanced uptake of NO₂ on urban grime was observed, with the obvious formation of HONO and NO from the heterogeneous reaction. The photo-enhanced γ was measured to be 1.9 × 10^?6 at 5% relative humidity (RH) and 5.8 × 10^?6 at 70% RH on urban grime, showing a positive RH dependence for both NO₂ uptake and HONO formation. The results demonstrate an important role of urban grime in the daytime NO₂-to-HONO conversion, and could be helpful to explain the unknown daytime HONO source in the polluted urban area.     

石家庄南郊黑碳气溶胶污染特征与来源分析

利用十波段黑碳仪实时监测石家庄南郊2018年9月—2019年7月大气中黑碳（Black Carbon，BC）质量浓度，并与同期CO、NO₂、SO₂质量浓度进行相关性分析，结合后向轨迹模型研究了该地区的BC质量浓度变化特征及潜在来源.结果表明，观测期间BC平均质量浓度为（4.35±3.59）μg·m^-3，最大频数浓度法估算的BC本底质量浓度为1.0 μg·m^-3，不同季节BC平均质量浓度变化趋势为：冬季>秋季>春季>夏季.BC质量浓度日变化具有双峰特征，高峰时段为6：00—9：00和19：00—22：00.BC气溶胶ngström指数α的分析及BC与CO、NO₂、SO₂相关性分析表明，以化石燃料为能源的工业源和交通源对石家庄南郊BC的贡献占主导地位.后向轨迹分析表明，石家庄南郊各季节BC主要受东向、东南向河北省内气团（占比35.46%~48.40%）和西向、西北向途经内蒙古、陕西北部、山西中部气团（占比15.60%~23.19%）的影响.浓度权重轨迹分析表明，BC潜在源区主要集中在河北南部、山西中部和河南北部.     

冬季PM2.5中无机水溶性离子与大气相对湿度的相关性

依托河北省灰霾污染防治重点实验室,对2019年11月26日—12月31日石家庄市大气PM_2.5中的NO₃^-和SO₄^2-进行连续在线观测,研究NO₃^-和SO₄^2-与环境空气相对湿度的相关性,解析冬季发生PM_2.5重污染天气的RH阈值.观测期间,RH为10%~60%时,NO₃^-的浓度与RH呈显著正相关,为PM_2.5中浓度最高的无机水溶性离子.RH超过70%后,NO₃^-与RH呈负相关,NO₃^-浓度和NOR开始下降.SO₄^2-浓度与RH在整个湿度区间均呈正相关.RH低于50%时,SO₂向SO₄^2-的转化以气相反应为主.RH高于50%以后,颗粒物达到潮解点,SO₂的主要反应转入液相,转化速率加快,SO₂液相反应贡献逐渐增加至64.6%.RH超过70%后,SO₄^2-成为PM_2.5中浓度最高的无机水溶性离子.RH超过PM_2.5潮解点以后,NO₃^-和SO₄^2-大量合成,推高PM_2.5环境浓度,易于形成重污染天气.     

华山地区PM2.5中无机离子垂直分布特征

2016年夏季在华山山腰及山脚设两个采样点（垂直高程相差约700 m）,运用大流量采样器进行每4 h 1次PM_2.5样品采集,对其无机离子进行分析,探讨其浓度、组成、垂直变化、日变化及酸度的特征.结果表明：采样期间,华山山腰及山脚的PM_2.5分别为：（46.9±38.2）μg·m^-3和（76.0±44.3）μg·m^-3,PM_2.5中无机离子分别为：（16.6±15.7）μg·m^-3和（24.0±15.0）μg·m^-3.两个点位无机离子浓度依次为：SO₄^2- > NO₃^- > NH₄⁺ > Ca²⁺.SO₄^2-、NO₃^-、NH₄⁺为主要组分,占华山山腰及山脚大气PM_2.5总离子质量浓度的89%和85%.线性回归分析显示：PM_2.5中的NH₄⁺在华山山腰主要以（NH₄）₂SO₄和NH₄NO₃的形式存在,而在华山山脚主要以NH₄HSO₄和NH₄NO₃的形式存在.华山山腰和山脚PM_2.5及其离子呈现出不同的日变化特征：山腰在12：00~16：00出现峰值,主要是因为边界层抬升和山谷风输送地表污染物的缘故;山脚则分别在白天08：00~12：00和夜晚00：00~04：00出现双峰值,这主要是由于早高峰交通排放增加和夜间大型载货卡车流量增大所致.利用阴阳离子当量平衡法及ISORROPIA Ⅱ模型进一步探讨了PM_2.5酸度特征,结果表明：华山山脚PM_2.5的酸度（pH=2.9±2.0）强于山腰（pH=3.2±2.3）.     

Interference from HONO in the measurement of ambient air NO2 via photolytic conversion and quantification of NO

The reference method to quantify mixing ratios of the criteria air pollutant nitrogen dioxide (NO₂) is NO-O₃ chemiluminescence (CL), in which mixing ratios of nitric oxide (NO) are measured by sampling ambient air directly, and mixing ratios of NO_x (= sum of NO and NO₂) are measured by converting NO₂ to NO using, for example, heated molybdenum catalyst or, more selectively, photolytic conversion (P-CL). In this work, the nitrous acid (HONO) interference in the measurement of NO₂ by P-CL was investigated. Results with two photolytic NO₂ converters are presented. The first used radiation centered at 395 nm, a wavelength region commonly utilized in P-CL. The second used light at 415 nm, where the overlap with the HONO absorption spectrum and hence its photolysis rate are less. Mixing ratios of NO₂, NO_x and HONO entering and exiting the converters were quantified by Thermal Dissociation Cavity Ring-down Spectroscopy (TD-CRDS). Both converters exhibited high NO₂ conversion efficiency (CF_NO2; > 90%) and partial conversion of HONO. Plots of CF against flow rate were consistent with photolysis frequencies of 4.2 s^-1 and 2.9 s^-1 for NO₂ and 0.25 s^-1 and 0.10 s^?1 for HONO at 395 nm and 415 nm, respectively. CF_HONO was larger than predicted from the overlap of the emission and HONO absorption spectra. The results imply that measurements of NO₂ by P-CL marginally but systematically overestimate true NO₂ concentrations, and that this interference should be considered in environments with high HONO:NO₂ ratios such as the marine boundary layer or in biomass burning plumes.     

Measurement of HONO flux using the aerodynamic gradient method over an agricultural field in the Huaihe River Basin, China

To investigate nitrous acid (HONO) levels and potential HONO sources above crop rotation fields. The HONO fluxes were measured by the aerodynamic gradient (AG) method from 14 December 2019 to 2 January 2020 over an agricultural field in the Huaihe River Basin. The ambient HONO levels were measured at two different heights (0.15 and 1.5 m), showing a typical diurnal cycle with low daytime levels and high nighttime levels. The upward HONO fluxes were mostly observed during the day, whereas deposition dominated at night. The diurnal variation of HONO flux followed solar radiation, with a noontime maximum of 0.2 nmol/(m²∙sec). The average upward HONO flux of 0.06 ± 0.17 nmol/(m²∙sec) indicated that the agricultural field was a net source for atmospheric HONO. The higher HONO/NO₂ ratio and NO₂–to–HONO conversion rate close to the surface suggested that nocturnal HONO was formed and released near the ground. The unknown HONO source was derived from the daytime HONO budget analysis, with an average strength of 0.31 ppbV/hr at noontime. The surface HONO flux, which was highly correlated with the photolysis frequency J(NO₂) (R² = 0.925) and the product of J(NO₂) × NO₂ (R² = 0.840), accounted for ∼23% of unknown daytime HONO source. The significant correlation between HONO fluxes and J(NO₂) suggests a light-driven HONO formation mechanism responsible for the surface HONO flux during daytime.     

Vertical distributions of wintertime atmospheric nitrogenous compounds and the corresponding OH radicals production in Leshan, southwest China

Ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) observations were operated from 02 to 21 December 2018 in Leshan, southwest China, to measure HONO, NO₂ and aerosol extinction vertical distributions, and these were the first MAX-DOAS measurement results in Sichuan Basin. During the measurement period, characteristic ranges for surface concentration were found to be 0.26–4.58 km^?1 and averaged at 0.93 km^?1 for aerosol extinction, 0.49 to 35.2 ppb and averaged at 4.57 ppb for NO₂ and 0.03 to 7.38 ppb and averaged at 1.05 ppb for HONO. Moreover, vertical profiles of aerosol, NO₂ and HONO were retrieved from MAX-DOAS measurements using the Heidelberg Profile (HEIPRO) algorithm. By analysing the vertical gradients of pollutants and meteorological information, we found that aerosol and HONO are strongly localised, while NO₂ is mainly transmitted from the north direction (city center direction). Nitrogen oxides such as HONO and NO₂ are important for the production of hydroxyl radical (OH) and oxidative capacity in the troposphere. In this study, the averaged value of OH production rate from HONO is about 0.63 ppb/hr and maximum value of ratio between OH production from HONO and from (HONO+O₃) is > 93% before12:00 in Leshan. In addition, combustion emission contributes to 26% for the source of HONO in Leshan, and we found that more NO₂ being converted to HONO under the conditions with high aerosol extinction coefficient and high relative humidity is also a dominant factor for the secondary produce of HONO.     

南京市黑碳气溶胶时间演变特征及其主要影响因素

为了研究南京市黑碳（black carbon,BC）气溶胶的时间演变特征及其主要影响因素,使用多波长Aethalometer（AE-33）每个季节选取典型月份观测了BC质量浓度,结合大气污染物数据、气象要素和边界层探测数据,分析了BC的季节变化、日变化、周末效应和来源特征.结果表明,南京的BC浓度具有明显的季节变化,春季[（3351±919）ng·m^-3] > 冬季[（3234±2102）ng·m^-3] > 秋季[（3064±967）ng·m^-3] > 夏季[（2632±1705）ng·m^-3].4个季节BC日变化均为双峰型分布,峰值分别位于06：00~08：00和21：00~23：00.BC不同季节的早晚高峰分布特征不同.早高峰春季BC浓度最高,晚高峰冬季浓度最高.冬季早高峰出现时间要比其他季节滞后2 h,而夏季晚高峰时间反而比其他季节提前2 h.风速对BC日变化季节分布差异的影响远大于相对湿度（relative humidity,RH）.逆温层结对大气污染物浓度的影响机制比较复杂,在不同季节中逆温的高度、厚度和逆温强度对污染物的影响机制不同.BC不同季节的周末效应不同,风速对BC周末效应的影响较小,逆温层结差异是造成BC周末效应的主要原因.南京地区液体燃料燃烧对BC的贡献较大,固体燃烧对BC贡献较小.     

NO-3和NO-2作为电子受体时的反硝化除磷实时控制

采用SBR厌氧/缺氧运行方式,研究了NO^-₃和NO^-₂作为电子受体时的反硝化除磷效能及ORP与pH作为反硝化除磷过程控制参数的可行性.结果表明,反硝化除磷过程中COD、磷酸盐、电子受体浓度与体系pH和ORP的变化具有较强的相关性.在厌氧阶段,当释磷结束时,pH值平台的出现指示了释磷的结束;在缺氧阶段,吸磷结束后,ORP出现拐点,标志着缺氧吸磷的完成.另外,考察了2种电子受体（NO^-₃和NO^-₂）反硝化除磷的效能.在以NO^-₃为电子受体的反应中,在缺氧初期30 min反应中,平均摄磷速率为32.68 mg/(L·h),每吸收1 mg PO^3-₄-Ｐ 约消耗1.14 mg NO^-₃-Ｎ.在以NO^-₂为电子受体的反应中,在缺氧初期30 min反应中,平均摄磷速率为17.66 mg/(L·h),每吸收1 mg PO^3-₄-Ｐ 约消耗1.57 mg NO^-₂-Ｎ.综上,提出pH和ORP可以作为2种电子受体（NO^-₃和NO^-₂）反硝化除磷的实时控制参数,并且,以NO^-₃为电子受体系统在摄磷方面优于NO^-₂电子受体系统.     

Evaluation and impact factors of indoor and outdoor gas-phase nitrous acid under different environmental conditions

As an important indoor pollutant, nitrous acid (HONO) can contribute to the concentration of indoor OH radicals by photolysis via sunlight penetrating into indoor environments, thus affecting the indoor oxidizing capability. In order to investigate the concentration of indoor HONO and its impact factors, three different indoor environments and two different locations in urban and suburban areas were selected to monitor indoor and outdoor pollutants simultaneously, including HONO, NO, NO₂, nitrogen oxides (NO_x), O₃, and particle mass concentration. In general, the concentration of indoor HONO was higher than that outdoors. In the urban area, indoor HONO with high average concentration (7.10 ppbV) was well-correlated with the temperature. In the suburban area, the concentration of indoor HONO was only about 1-2 ppbV, and had a good correlation with indoor relative humidity. It was mainly attributed to the heterogeneous reaction of NO₂ on indoor surfaces. The sunlight penetrating into indoor environments from outside had a great influence on the concentration of indoor HONO, leading to a concentration of indoor HONO close to that outdoors.     

典型华北农村地区冬季HONO的浓度水平及来源分析

气态亚硝酸(HONO)容易光解,是对流层大气羟基自由基(·OH)的重要来源之一,对区域二次污染的形成具有重要作用.我国在大气HONO观测研究方面主要集中在一些城市区域,而在我国北方农村区域的研究还鲜见报道.为此,本文利用亚硝酸在线分析仪(long path absorption photo meter,LOPAP)于2017年11月在中国科学院农村环境研究站(河北省望都县东白陀村)开展了为期一个月的HONO外场观测,并分析了HONO的浓度水平、变化特征及收支情况.大气HONO的浓度在观测期间呈现夜间高、白天低的日变化特征,夜间最高浓度(体积分数,下同)可达约3. 70×10-9,中午最低浓度也维持在0. 10×10-9以上,表明农村区域存在比较强的HONO来源.采暖前后CO浓度显著提高,而HONO浓度无显著变化,说明供暖燃烧对HONO的贡献较小;夜间机动车直接排放在污染天气和清洁天气条件下对HONO的贡献分别为23. 20%和31. 20%,说明在污染天气条件下存在着某些较强的HONO源;夜间·OH与NO的均相反应HONO平均生成速率可高达0. 40×10-9h-1,比NO2的非均相反应HONO生成速率(0. 24×10-9h-1)高0. 67倍,是HONO的主要来源; HONO在白天存在着很强的未知源,其强度可达1. 37×10-9h-1,对于HONO的贡献达到50%左右.     

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.     

Reactive uptake of NO2 on volcanic particles: A possible source of HONO in the atmosphere

The heterogeneous degradation of nitrogen dioxide (NO₂) on five samples of natural Icelandic volcanic particles has been investigated. Laboratory experiments were carried out under simulated atmospheric conditions using a coated wall flow tube (CWFT). The CWFT reactor was coupled to a blue light nitrogen oxides analyzer (NO_x analyzer), and a long path absorption photometer (LOPAP) to monitor in real time the concentrations of NO₂, NO and HONO, respectively. Under dark and ambient relative humidity conditions, the steady state uptake coefficients of NO₂ varied significantly between the volcanic samples probably due to differences in magma composition and morphological variation related with the density of surface OH groups. The irradiation of the surface with simulated sunlight enhanced the uptake coefficients by a factor of three indicating that photo-induced processes on the surface of the dust occur. Furthermore, the product yields of NO and HONO were determined under both dark and simulated sunlight conditions. The relative humidity was found to influence the distribution of gaseous products, promoting the formation of gaseous HONO. A detailed reaction mechanism is proposed that supports our experimental observations. Regarding the atmospheric implications, our results suggest that the NO₂ degradation on volcanic particles and the corresponding formation of HONO is expected to be significant during volcanic dust storms or after a volcanic eruption.     

京津冀机场群飞机LTO大气污染物排放清单

基于国际民航组织(ICAO)标准排放模型,调查搜集京津冀机场群9个机场实际航班情况,充分考虑了大气混合层高度的影响,采用EPA方法修正运行时间,精确估算了2018～2019航季年(364 d)京津冀机场群飞机起飞着陆循环(LTO)大气污染物排放清单.结果表明, 2018～2019航季年京津冀机场群飞机LTO循环NO_x、 CO、 SO_2、 HC和PM排放总量分别为10 720.5、 3 972.2、 407.8、 508.0和53.7 t.其中,冬春航季排放量分别为4 290.2、 1 646.7、 168.3、 220.1和22.4 t;夏秋航季排放量分别为6 430.3、 2 325.5、 239.5、 287.9和31.3 t.从空间分布来看,北京首都机场是该机场群大气污染物排放量最多的机场.从时间分布来看,07:00～08:00处于排放量最高峰, 12:00～20:00处于中等偏高排放水平, 21:00之后排放量相对较低.飞机在LTO循环中NO_x和CO排放量较多,PM排放量最少.各污染物不同工作模式下的排放情况差异明显.在该机场群起降所有机型中,B777单位LTO循环排放污染物最多,B737最少,B787单位LTO循环排放HC最低.     

北京典型跑步区域空气污染特征及跑步者呼吸暴露

为研究北京市跑步人群运动过程中主要空气污染物的人体呼吸暴露情况,根据2016年4月、7月、10月和2017年1月北京典型的公园跑步区域(天坛公园、奥体中心)、路跑区域(前门东大街、永定内大街)、背景区域(定陵)PM_(2.5)、CO、O3和NO2等污染物在线监测站点数据,分析各污染物的质量浓度时空变化特征,并对102位跑步爱好者进行调查,采用人体呼吸暴露数值模型,研究跑步爱好者污染物吸入剂量的时空差异.结果表明,典型跑步区域CO、NO2和PM_(2.5)浓度冬季高,春季和夏季较低,O3浓度则呈现春季和夏季高、秋季和冬季低;下午时段(16:00~18:00)CO、NO2、PM_(2.5)浓度较低,早晨(06:00~08:00)和晚上(18:00~20:00)时段O3浓度较低,适宜跑步;道路与邻近公园的污染物浓度呈线性相关,CO路侧浓度与公园内基本一致(c路/c园=1.01,R2=0.93),NO2和PM_(2.5)路侧浓度较公园内高,c路/c园分别为0.56和1.19,O3浓度路侧低于公园内(c路/c园=0.74,R2=0.97);92%的跑步爱好者在中度及以上污染天气情况下停止户外运动,选择在公园内和晚上跑步的跑者占比分别为62.7%和66.7%,64.7%的跑者单次跑步里程在10~20 km;下午和晚上跑步时个体的CO、NO2、PM_(2.5)吸入剂量较晨跑低,但O3吸入剂量较高,春季、夏季夜跑时可选择20:00以后时段,能降低O3吸入剂量;路跑条件下个体的CO、NO2和PM_(2.5)的吸入剂量总体要高于公园跑,但O3吸入剂量刚好相反.     

An online monitoring system for atmospheric nitrous acid (HONO) based on stripping coil and ion chromatography

A new instrument for measuring atmospheric nitrous acid(HONO) was developed,consisting of a double-wall glass stripping coil sampler coupled with ion chromatography(SC-IC).SC-IC is featured by small size(50 × 35 × 25 cm) and modular construction,including three independent parts:the sampling unit,the transfer and supporting unit,and the detection unit.High collection efficiency(> 99%) was achieved with 25 μmol/L Na2CO3 as absorption solution even in the presence of highly acidic compounds.This instrument has a detection limit of 8 pptv at 15 min time resolution,with a measurement uncertainty of 7%.Potential interferences from NOx,NO2+SO2,NO2+VOCs,HONO+O3,HNO3,peroxyacetyl nitrite(PAN) and particle nitrite were quantified in laboratory studies and were found to be insignificant under typical atmospheric conditions.Within the framework of the 3C-STAR project,inter-comparison between the SC-IC and LOPAP(long path liquid absorption photometer) was conducted at a rural site in the Pearl River Delta.Good agreement was achieved between the two instruments over three weeks.Both instruments determined a clear diurnal profile of ambient HONO concentrations from 0.1 to 2.5 ppbv.However,deviations were found for low ambient HONO concentrations(i.e.< 0.3 ppbv),which cannot be explained by previous investigated interference species.To accurately determine the HONO budget under illuminated conditions,more intercomparison of HONO measurement techniques is still needed in future studies,especially at low HONO concentrations.     

NOx和/或NH3气氛下SO2在高岭土表面非均相转化的实验研究

利用自制气溶胶反应器研究了NO_x和/或NH_3气氛下SO_2在高岭土表面的非均相转化过程,应用扫描电镜(SEM)对高岭土颗粒物形貌进行了表征.结果表明:高岭土颗粒表面的SO_2非均相转化致使其成分和形貌产生了较大变化.相同实验条件下,SO_2转化的协同作用程度由高到低依次为NH_3、NO_x/NH_3和NO_x气氛,相对湿度40%、有光照条件下,SO_2转化量增幅最高可分别达125%、75%和50%.所有气氛下,协同作用在无光照时在高相对湿度(40%~70%)区间更为突出,有光照时其显著性则体现在低相对湿度(20%~40%)区间.SO_2、NO_x、NH_3三者共存时,在高岭土颗粒表面发生的非均相反应过程既有协同作用又存在竞争反应.