Tropospheric Ozone at High Latitudes in Clean and Polluted Air Masses, a Climatological Study

Several years of continuous measurements of surfaceozone at Norwegian monitoring sites are studied in aclimatological way. The monitoring sites are at rurallocations extending from 58°N, a few hundredkilometers from the European continent and into theArctic at 79°N. The ozone observations are sorted intoclasses of integrated NO_x emissions along 96 h backtrajectories. The average seasonal cycles of ozone areestimated for each class separately. The differencesindicate the change from the background air due toanthropogenic emissions. The average seasonal cycle ofozone in the cleanest air masses showed a maximum inspring and a minimum during summer and autumn at allsites, but the spring maximum was more pronounced atthe southernmost locations. Polluted air masses showedan ozone deficit during winter and a surplus duringsummer. The deviation from the background was clearlylinked to the integrated NO_x emission along thetrajectories. In summer the calculations indicate thatthe number of ozone molecules formed per NO_x moleculedrops with increasing emissions. The average seasonalcycle of ozone at Birkenes for different transportsectors indicate that the most pronounced ozoneformation takes place in air masses from E-Europe/Russia.     

Tropospheric ozone and oxides of nitrogen over the north-western Pacific in summer

In summer, atmospheric ozone was measured from an aircraft platform simultaneously with nitric oxide (NO), oxides of nitrogen (NO _y ), and water vapor over the Pacific Ocean in east Asia from 34° N to 19° N along the longitude of 138±3°E. NO _y was measured with the aid of a ferrous sulfate converter. The altitude covered was from 0.5 to 5 km. A good correlation in the smoothed meridional distributions between ozone and NO _y was seen. In particular, north of 25° N, ozone and NO _y mixing ratios were considerably higher than those observed in tropical marine air south of 25° N. NO _y and O₃ reached a minimum of 50 pptv and 4 ppbv respectively in the boundary layer at a latitude of 20° N. The NO concentration between 2 and 5 km at the same latitude was 30 pptv. The profiles of ozone and water vapor mixing ratios were highly anti-correlated between 25° N and 20° N. In contrast, it was much poorer at the latitude of 33° N, suggesting a net photochemical production of ozone there.     

Observation of Filterable Bromine Variabilities During Arctic Tropospheric Ozone Depletion Events in High (1hour) Time Resolution

The halogen ions Br^- and Cl^- together with NO₃ ^-, SO₄ ⁼, MSA^- (methane sulfonate), Na⁺ and NH₄ ⁺ were analysed by ion chromatography in extracts of more than 800 aerosol cellulose filter samples taken at Ny Ålesund, Svalbard (79°N, 12°E) in spring 1996 (March 27 - May 16) within the European Union project ARCTOC (Arctic Tropospheric Ozone Chemistry). Anticorrelated variations between f-Br (filterable bromine, i.e. water soluble bromine species that can be collected by aerosol filters) and ozone within the arctic troposphere were evaluated at a resolution of 1 or 2 hours for periods with depleted ozone and 4 hours at normal ozone. A mean f-Br concentration of 11 ng m^-3 (0.14 nmol m^-3) was observed for the whole campaign, while maximum concentrations of 80 ng m^-3 (1 nmol m^-3) were detected during two total O₃-depletion events (O₃ drop to mixing ratios below the detection limit of < 2 ppb). Anticorrelation between f-Br and O₃ was also seen during minor O₃-depletion episodes (sudden drop in O₃ by at least 10 ppb, but O₃ still exceeding the detection limit) and even for ozone variations near its background level (40-50 ppb). A time lag of about 10 hours between the change of ozone and of f-Br concentrations could only be found during a total ozone depletion event, when f-Br reached its maximum values several hours after ozone was totally destroyed. Bromine oxide (BrO) concentrations, measured by DOAS (Differential Optical Absorption Spectroscopy), and f-Br showed a coincident variability during almost the entire campaign (except in the case of total O₃-loss). Frequently enhanced anthropogenic nitrate and sulphate concentrations were observed during O₃-depletion periods. At O₃ concentrations < 10 ppb sulphate and nitrate exceed their typical mean level by 54% and 77%, respectively. This may indicate a possible connection between acidity and halogen release.     

SURFACE OZONE CHARACTERISTICS AT THREE STATIONS IN GAW OF WMO IN CHINA*

The characteristics of surface O₃ on clear days at Waliguan Observatory,Lin'an regional station and Longfengshan regional station in China were analyzed in this paper.The three stations belong to Global Atmospheric Watch(GAW)of WMO.There was obvious daily variation on clear days at Lin'an.with maximum(42.9 ppb)and minimum(20.3 ppb)of daily range appearing in spring and summer,respectively.The daily variation was more regular at Lonfengshan than at Lin'an.The maximum(about 27 ppb)appeared in autumn at Longfengshan.There was no obvious daily variation and also daily range was smaller in other seasons except weaker daily variation in summer at Waliguan.But the surface O₃ concentration(SOC)in summer was higher than that in winter at Waliguan.The SOC on clear days of summer at Waliguan was over 20 ppb higher than at Longfengshan and Lin'an.The global radiation and NO_x concentration were the main factors which control the SOC on clear days at Longfengshan and Lin'an.and played important role in different seasons and areas.The transportation of air flow around the area of Qinghai-Xizang(Tibet)Plateau was the main cause for high SOC and weak daily variation in summer at Waliguan.The similar effect of transportation was obtained at the Mauna Loa Observatory.The distribution characteristics of SOC increasing with height in the troposphere determined the difference of SOC between East China and West China.     

Measurements of ozone and its precursor nitrogen dioxide and crop yield losses due to cumulative ozone exposures over 40 ppb (AOT40) in rural coastal southern India

Measurements of ground level ozone (O₃), nitrogen dioxide (NO₂) and meteorological parameters (air temperature, relative humidity and wind speed and direction) has been made for 3 years from March 2007 to February 2010 at Nagercoil (8.2°N, 77.5°E, 23 m above sea level), an equatorial rural coastal site of southern India. The monthly average of daytime maximum of O₃ concentrations ranged from 28 to 50 parts per billion (ppb) with an annual average of 19.8 ppb. Similarly, monthly average of NO₂ concentration ranged from 3.4 ppb to 7.7 ppb with an annual average of 5.3 ppb. The monthly variation of meteorological parameters shows the little changes being a coastal site. The estimated summer crops yield losses by 1.1–15.6 % from present O₃ concentration level associated with AOT40 index 3.1–5 ppm h.     

RESEARCH ON SURFACE O3 WITH METEOROLOGICAL CONDITIONS UNDER ATMOSPHERIC BACKGROUND CONDITIONS IN NORTHEAST CHINA*

Surface O₃ concentration and its precursors have been observed at Longfengshan station,Heilongjiang Province for a period of one year from August 13,1994 to July 30,1995. Relationship between surface O₃ and the meteorological conditions during this period is analyzed in this study.Observation results show that diurnal variation of surface O₃ follows a pattern of double-peaks with amplitude of 27-28 ppb under fine days in summer and autumn.Although the diurnal variation is small(14 ppb),it is still detectable when it is overcast.Diurnal variation of O₃ is irregular under rainy days.Surface O₃ concentration rises when wind speed starts to increase at 0800 BT(Beijing Time)from 0 to 6 m s^-1in autumn,winter and summer.Relative high surface O₃ concentration is noticed frequently when S,SSW,SW and WSW wind are encountered at the station during all seasons.At 0800 BT and 1400 BT the surface O₃ concentration increases with the increase of global radiation accordingly during fine days in winter,spring and autumn.During fine days average peak of O₃ concentration in summer is 20 ppb higher than that in winter while the average peak of global radiation in summer is almost twice as high as that in winter.The average surface O₃ concentration under fine days in autumn at Longfengshan station is 14 ppb lower in comparison to the observation results from Lin'an station where Lin'an is at about the same longitude and lower latitude,with same environment,which is mainly caused by the difference of global radiation due to different latitudes in these two areas(difference of average peak global radiation about 100 W m^-2).     

全球闪电活动与对流层上部NO及O3的相关性分析

为了解闪电对对流层上部微量气体的贡献,利用全球水资源和气候中心(GHRC)提供的1995年4月—2006年6月的闪电卫星格点资料,以及高层大气研究卫星(UARS)上的卤素掩星试验(HALOE)1991年10月—2005年11月的观测资料,分析了全球闪电与对流层上部NO和O3体积分数的时空分布特征及其相关性。结果表明:全球闪电12、1、2月集中在南半球,6—8月集中在北半球,全球闪电的季节分布与NO、O3类似;NO体积分数在350 h Pa附近达到最大,该高度的南半球NO体积分数变化范围为7×10-12~11×10-12、北半球为3×10-12~17×10-12;450~300 h Pa,北半球夏季O3体积分数呈明显增加趋势,且同一高度上夏季的值比年平均值大25%左右,南半球夏季O3体积分数高于冬季,但差异并不大。结论进一步证明了闪电与对流层上部NO及O3的密切关系,也为研究全球气候变化提供有力证据。     

闪电产生氮氧化物对青藏高原臭氧低谷形成的影响

为了进一步了解青藏高原闪电的产生氮氧化物（LNO_x）经由光化学反应对O₃浓度变化及夏季O₃低谷形成的可能影响,本文利用2005~2013年由OMI卫星得到的对流层NO₂垂直浓度柱（NO₂ VCD）、O₃总浓度柱（TOC）和O₃廓线以及星载光学瞬变探测器OTD和闪电成像仪LIS获取的总闪电数资料,对青藏高原和同纬度长江中下游地区的TOC和NO₂ VCD月均值时空分布特征、闪电与NO₂ VCD的相关性和O₃的垂直分布特征及其与LNO_x的关系进行了对比分析。结果表明,青藏高原的O₃低谷主要出现在夏季和秋季,其TOC值比同纬度长江中下游地区低约10~15 DU（Dobson unit）。青藏高原NO₂VCD总体较小,表现为夏高冬低的分布特征。青藏高原夏季O₃浓度受南亚高压的影响总体呈减小趋势,但因强雷暴天气导致对流层中上部LNO_x浓度升高,并随强上升气流向对流层顶输送,同时通过光化学反应使O₃浓度增加,缩小了青藏高原和同纬度地区的O₃浓度差,减缓了O₃总浓度的下降,抑制了夏季O₃低谷的进一步深化。     

Seasonal and Diurnal Variation of Surface Ozone and a Preliminary Analysis of Exceedance of its Critical Levels at a Semi-arid Site in India

The mixing ratios of surface O₃ were measured at St. John's College, Agra, an urban and traffic influenced area for the period of 2000–2002. The monthly averaged O₃ mixing ratios ranged between 8 to 40 ppb with an annual average of 21 ppb. Strong diurnal and seasonal variations in O₃ mixing ratios were observed throughout the year except for monsoon season. The mixing ratios of O₃ follow the surface temperature cycle and solar radiation (r = 0.72 and r = 0.65 with temperature and solar radiation, respectively). Concentrations were higher with winds associated with NE and NW direction indicating the impact of pollution sources on surface O₃ concentration. Exceedance of ozone critical level was calculated using the AOT 40 index and found to be 840 ppb.h and 2430 ppb.h for summer and winter seasons, respectively. The present O₃ exposures are lower than the critical level of O₃ and suggest that the present level of O₃ does not have any impact on reduction in crop yields.     

Lower/middle tropospheric ozone variability in Senegal during pre-monsoon and monsoon periods of summer 2008: observations and model results

During the summer (8 June through 3 September) of 2008, 9 ozone profiles are examined from Dakar, Senegal (14.75°N, 17.49°W) to investigate ozone (O₃) variability in the lower/middle troposphere during the pre-monsoon and monsoon periods. Results during June 2008 (pre-monsoon period) show a reduction in O₃ concentrations, especially in the 850–700 hPa layer with Saharan Air Layer (SAL) events. However, O₃ concentrations are increased in the 950–900 hPa layer where the peak of the inversion is found and presumably the highest dust concentrations. We also use the WRF-CHEM model to gain greater insights for observations of reduced O₃ concentrations during the monsoon periods. In the transition period between 26 June and 2 July in the lower troposphere (925–600 hPa), a significant increase in O₃ concentrations (10–20 ppb) occur which we suggest is caused by enhanced biogenic NO_X emissions from Sahelian soils following rain events on 28 June and 1 July. The results suggest that during the pre-monsoon period ozone concentrations in the lower troposphere are controlled by the SAL, reducing ozone concentrations through heterogeneous chemical processes. At the base of the SAL we also find elevated levels of ozone, which we attribute to biogenic sources of NO_X from Saharan dust that are released in the presence of moist conditions. Once the monsoon period commences, lower ozone concentrations are observed and modeled which we attribute to the dry deposition of ozone and episodes of ozone poor air that is horizontally transported into the Sahel from low latitudes by African Easterly Waves (AEWs).     

Measurements of Trace Substances in the Arctic Troposphere as Potential Precursors and Constituents of Arctic Haze

During two measuring campaigns in early spring 1994 and 1995 (March/April) and one campaign in summer 1994, measurements of ozone, PAN, sulfur dioxide, nitric acid, and particulate nitrate, sulfate, and ammonium (only 1995) were recorded in the Arctic. Observations were made by aircraft at various sites in the eastern and western Arctic. Ozone concentrations showed a steady increase with altitude both in spring and summer. During five flights in springtime, low ozone events (LOEs) could be observed near the surface and up to altitudes of 2000 m. SO₂ background concentrations, ranging from detection limit (0.5 nmol/m³) to 5 nmol/m³, were observed during both spring and summer. Distinct maxima up to 55 nmol/m³ in lower altitudes were only obtained in springtime. Concentrations of the organic nitrate PAN were within a similar range as those of the inorganic nitrate HNO₃ during spring campaigns. In contrast, concentrations of particulate nitrate were one half an order of magnitude lower. HNO₃ concentrations increased significantly with altitude. Evidently, HNO₃ was intruded from the stratosphere into the troposphere. Sulfate concentrations ranged between 5 and 30 nmol/m³; ammonium concentrations were obtained within a range from 10 to 50 nmol/m³.     

Growth of monodisperse,submicron aerosol particles exposed to SO2, H2O2, and NH3

The growth of monodisperse particles (0.07 to 0.5 µm) exposed to SO₂ (0–860 ppb), H₂O₂ (0–150 ppb) and sometimes NH₃ (0–550 ppb) in purified air at 22 °C at relative humidities ranging from 25 to 75% were measured using the Tandem Differential Mobility Analyzer technique. The experiments were performed in a flow reactor with aqueous (NH₄)₂SO₄ and Na₂SO₄ droplets. For (NH₄)₂SO₄ droplets the fractional diameter growth was independent of size above 0.3 µm but decreased with decreasing size below that. When NH₃ was added the fractional growth increased with decreasing size. Measurements were compared with predictions of a model that accounts for solubility of the reactive gases, the liquid phase oxidation of SO₂ by H₂O₂, and ionic equilibria. Agreement between measured and predicted droplet growth is reasonable when the ionic strength effects are included. Theory and experiments suggest that NH₃ evaporation is responsible for the decrease in relative growth rates for small aqueous ammonium sulfate particles. The observed droplet growth rates are too slow to explain observed growth rates of secondary atmospheric sulfate particles.     

Surface ozone measurements in the Venezuelan tropical savannah

A one-year set of surface ozone measurements in a four-station network located in the Venezuelan savannah is reported. The diurnal ozone variation is typical of continental stations with a maximum in the afternoon, when vertical turbulent mixing is strongest. The annual O₃ average concentration, based on the monthly averages of daily maxima, was 17±2 ppb, which is in good agreement with values reported for similar latitudes. The boundary-layer ozone levels did not fall below 8 ppb, in contrast with previous sporadic measurements made in tropical latitudes. No evidence was found that mesoscale O₃ downdrafts in the ITCZ in the South American continent are an important source of surface ozone. Finally, it is suggested that the relatively high ozone levels observed at the end of the dry season are probably of photochemical origin.     

临安冬夏季SO2、NO2和O3体积分数特征及与气象条件的关系

对临安大气本底站2003-2004年冬、夏季二氧化氮(NO2)、二氧化硫(SO2)、臭氧(O3)进行了分析.结果表明:冬季NO2和SO2平均体积分数分别为19.48×10-9和35.74 x10-9,而夏季的平均体积分数分别为4.81×10-9和8.12×10-9,冬季高于夏季;O3在夏季的平均体积分数为33.55×10-9,略高于冬季的25.44×10-9;夜间NO2和SO2体积分数比白天高,并且NO2呈明显的单峰单谷型分布,O3也呈单峰型但峰值出现在白天.NO2、SO2体积分数存在着明显的“假日效应”,假日比非假日低,周五高于假日和非假日;但O3体积分数没有明显的假日效应.降水对SO2有明显的清除作用,但对NO2的清除作用不明显.与风向对比发现,夏季高体积分数的NO2、SO2都受到NW、WNW风的影响,冬季则分别受NE和SW、SSW风的影响;而O3受风向的影响较复杂,与局地光化学反应有关.     

西太平洋地区大气边界层内臭氧的季节变化及其影响因子分析

利用臭氧探空资料,分析了西太平洋地区香港(Hong Kong)、那霸(Naha)和札幌(Sapporo)三个站点2000~2010年期间大气边界层内臭氧(O₃)的季节分布和年变化趋势。结果表明,三个站点O₃的季节分布存在明显的差异。其中,那霸和香港大气边界层内O₃季节平均呈双峰值分布,其峰值分别出现在春季和秋季;而札幌站为单峰分布,峰值出现在春季。造成季节分布差异的主要原因包括人为污染源和自然因素如气象条件。另外,三个站点大气边界层内O₃均呈上升趋势。其中札幌、那霸上升最快,分别达0.80 ppb a-1和0.77 ppb a-1。(ppb表示10-9,下同)香港的年际增长较不明显,但秋季增长却非常明显,高达1.21 ppb a-1。结合GOME (Global Ozone Monitoring Experiment) 和SCIAMACHY (Scanning Imaging Absorption Spectro Meter for Atmospheric Chartography)卫星反演的NO₂数据发现,过去10年中国京津唐和东北地区的对流层内NO₂柱总量增加极为迅速。这些O₃前体物通过远距离输送是导致札幌、那霸O₃浓度增加的主要原因之一。珠江三角洲人为污染源的增加及偏北气流的影响,是导致香港地区秋季O₃增加的主要原因。     

Measurements of Photolyzable Halogen Compounds and Bromine Radicals During the Polar Sunrise Experiment 1997

As part of the Polar Sunrise Experiment (PSE) 1997, concentrations of halogen species thought to be involved in ground level Arctic ozone depletion were made at Alert, NWT, Canada (82.5°N, 62.3°W) during the months of March and April, 1997. Measurements were made of photolyzable chlorine (Cl₂ and HOCl) and bromine (Br₂ and HOBr) using the Photoactive Halogen Detector (PHD), and bromine radicals (BrO_x) using a modified radical amplifier. During the sampling period between Julian Day 86 (March 27) and Day 102 (April 12), two ozone depletion episodes occurred, the most notable being on days 96-99, when ozone levels were below detectable limits (1 ppbv). Concentrations of BrO_x above the 4 pptv detection limit were found for a significant part of the study, both during and outside of depletion events. The highest BrO_x concentrations were observed at the end of the depletion event, when the concentration reached 15 pptv. We found substantial amounts of Br₂ in the absence of O₃, indicating that O₃ is not a necessary requirement for production of Br₂. There is also Br₂ present when winds are from the south, implying local scale (e.g. from the snowpack) production. During the principal O₃ depletion event, the HOBr concentration rose to 260 pptv, coincident with the BrO_x maximum. This implies a steady state HO₂ concentration of 6 pptv. During a partial O₃ depletion event, we estimate that the flux of Br₂ from the surface is about 10 times greater than that for Cl₂.     

东亚季风转换对西北太平洋近地面O3春季高值的影响

以东亚酸沉降监测网近地面O3资料,结合NCEP/NCAR的全球再分析风场、NOAA总云量及全球降水气候项目降水资料,分析2000～2007年东亚西太平洋地区近地层O3的区域和季节变化,重点分析不同站点O3月均浓度最大值时间差异的原因。结果表明,东亚以及大部分北半球中纬度清洁背景地区,近地层O3春季最高、夏季最低是广泛存在的现象。东亚夏季风的推进过程造成不同地区春季O3月均最大值出现的时间略有不同,Ogasawara和Hedo站O3浓度在3月达最大值,而Rishiri、Happo、Oki和Cheju站在4、5月达最大值。2007年副热带高压西进较晚且推进过程受阻导致Happo站2007年春季O3浓度高于气候平均值,Cheju地区2007年5月O3浓度达最大;2004年东亚夏季风爆发较早导致Hedo站2004年春季O3浓度明显低于平均值。     

Measurement of PAN in the Polluted Boundary Layer and Free Troposphere Using a Luminol-NO2 Detector Combined with a Thermal Converter

Peroxyacetyl nitrate (PAN,CH³C(O)O₂NO₂) has been measured inthe polluted boundary layer and free troposphere by thermal conversion tonitrogen dioxide (NO₂) followed by detection of thedecomposition product with a Scintrex LMA-3 NO₂-luminolinstrument. Following laboratory tests of the efficiency of PAN conversionand investigations of possible interferences, the technique was evaluated atthe West Beckham TOR (Tropospheric Ozone Research) Station near the northNorfolk coast in Eastern England between September 1989 and August 1990. PANmeasured by the new technique was reasonably well correlated with PANrecorded using electron capture gas chromatography (EC/GC). PAN was alsowell correlated with ozone (O³) in the summer months. Springand autumn episodes of simultaneously high concentrations of PAN andO³ were examined in conjunction with air parcelback-trajectories and synoptic- and local-scale meteorology in a study ofthe sources of photooxidants on the east coast of England. Spring-timemeasurements of PAN made in the free troposphere in a light aircraft ataltitudes up to 3.1 km showed the presence of 0.54 and 0.26 ppbv PAN inpolar maritime and mid-latitude oceanic air masses, respectively. Thetechnique is particularly suited to airborne applications because potentialinterferences are minimised and the frequency of measurements is higher thangenerally achieved with EC/GC methods.     

Surface ozone concentrations in Agra: links with the prevailing meteorological parameters

Measurements of surface ozone (O₃), nitric oxide (NO), nitrogen dioxide (NO₂), oxides of nitrogen (NO_x=NO+NO₂) and meteorological parameters have been made at Agra (North Central India, 27°10??N, 78°05??E) in post monsoon and winter season. The diurnal variation in O₃ concentration shows daytime in situ photochemical production with diurnal maximum in noon hours ranging from 51 to 54 ppb in post monsoon and from 76 to 82 ppb in winter, while minimum (16?C24 ppb) during nighttime and early morning hours. Average 8-h O₃ concentration varied from 12.4 to 83.9 ppb. The relationship between meteorological parameters (solar radiation intensity, temperature, relative humidity, wind speed and wind direction) and surface O₃ variability was studied using principal component analysis (PCA), multiple linear regression (MLR) and correlation analysis (CA). PCA and MLR of daily mean O₃ concentrations on meteorological parameters explain up to 80 % of day to day ozone variability. Correlation with meteorology is strongly emphasized on days having strong solar radiation intensity and longer sunshine time.     

华南地区春季平流层入侵对对流层低层臭氧影响的模拟研究

利用中尺度大气化学模式WRF/Chem对2013年3月6日华南地区一次平流层入侵事件及其对对流层低层臭氧的影响进行模拟研究。通过加入UBC（Upper Boundary Condition）上边界处理方案,弥补WRF/Chem模式未考虑平流层臭氧化学反应的不足。结合臭氧探空廓线资料、地面O₃、CO、NO_x、相对湿度、温度和风速等观测资料以及再分析资料对模拟结果进行定量评估,结果表明模式能较为真实地模拟本次平流层入侵过程。模拟分析进一步揭示:（1）副热带高空急流是本次平流层入侵的主要原因。当华南地区处在副热带急流入口区左侧下沉区域时,平流层入侵将富含臭氧的干燥空气输送到对流层中低层。（2）本次平流层入侵对对流层低层臭氧收支有重要影响,导致香港地区近地层臭氧体积混合比浓度明显上升,如塔门站夜间臭氧浓度升高21.3 ppb（1 ppb=1×10-9）。地面气象场和化学物种的分析进一步确认了平流层入侵的贡献。（3）采用动力学对流层顶高度时零维箱式模型和Wei公式计算得到的平流层入侵通量相当,分别为-1.42×10-3 kg m-2 s-1和-1.59×10-3 kg m-2 s-1,这一结果与前人研究相吻合,且与采用热力学对流层顶高度计算所得到的结果具有可比性。