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.     

Comparison of Measured Ozone Production Efficiencies in the Marine Boundary Layer at Two European Coastal Sites under Different Pollution Regimes

Ozone production efficiencies (E_N), which can be defined as the netnumber of ozone molecules produced per molecule of NO_xoxidised, have been calculated from measurements taken during three intensive field campaigns (one in the spring, EASE 96, and two in the summer, EASE 97 and TIGER 95), at two European coastal sites (Mace Head, Ireland (EASE) and Weybourne, Norfolk (TIGER)) impacted by polluted air masses originating from both the U.K. and continental Europe, as well as relatively clean oceanic air masses from the Arctic and Atlantic. From a detailed wind sector analysis of the EASE 96 and 97 data it is clear that two general types of pollution regime were encountered at Mace Head. The calculated ozone production efficiency in clean oceanic air masses was approximately 65, which contrasted to more polluted air, from the U.K. and the continental European plume, where the efficiency decreased to between 4 and 6. The latter values of E_Nagree well with literature measurements conducted downwind of various urban centres in the U.S. and Europe, which are summarised in a wide-ranging review table. The E_N value calculated for clean oceanic air is effectivelyan upper limit, owing to the relatively rapid deposition of HNO₃ tothe ocean. Consideration of the variation of E_N with NO_x forthe three campaigns suggests that ozone production efficiency is relatively insensitive to both geographical location and season. The measuredE_N values are also compared with values derived from steady-state expressions. An observed anti-correlation between E_N and measured ozone tendencyis briefly discussed.     

A Seasonal Comparison of the Ozone Photochemistry in Clean and Polluted Air Masses at Mace Head, Ireland

Measurements of the sum of peroxy radicals [HO₂ + RO₂],NO_x (NO + NO₂) and NO_y (the sum of oxidisednitrogen species) made at Mace Head, on the Atlantic coast of Ireland in summer 1996 and spring 1997 are presented. Together with a suite of ancillary measurements, including the photolysis frequencies of O₃ O(¹D)(j(O¹D)) and NO₂ (j(NO₂)), the measured peroxy radicals are used to calculate meandailyozone tendency (defined as the difference of the in-situphotochemical ozone production and loss rates); these values are compared with values derived from the photochemical stationary state (PSS) expression. Although the correlation between the two sets of values is good, the PSS values are found to be significantly larger than those derived from the peroxy radical measurements, on average, in line with previous published work. Possible sources of error in these calculations are discussed in detail. The data are further divided up into five wind sectors, according to the instantaneous wind direction measured at the research station. Calculation of mean ozone tendencies by wind sector shows that ozone productivity was higher during spring (April–May) 1997 than during summer (July–August) 1996across all airmasses, suggesting that tropospheric photochemistry plays an important role in the widely-reported spring ozone maximum in the Northern Hemisphere. Ozone tendencies were close to zero for the relatively unpolluted south-west, west and north-west wind sectors in the summer campaign, whereas ozone productivity was greatest in the polluted south-east sector for both campaigns. Daytime weighted average ozone tendencies were +(0.3± 0.1) ppbv h^–1 for summer 1996 and +(1.0± 0.5) ppbvh^–1 for spring 1997. These figures reflect the higher mixing ratios of ozone precursors in spring overall, as well as the higher proportion of polluted air masses from the south-east arriving at the site during the spring campaign. The ozone compensation point, where photochemical ozone destruction and production processes are in balance, is calculated to be ca. 14 pptv NO for both campaigns.     

On the Budget of OH Radicals and Ozone in an Urban Plume from the Decay of C5–C8 Hydrocarbons and NOx

Simultaneous measurements of ozone and ozoneprecursors were made during a field campaign atSchauinsland in the Black Forest and in the valleynorth of Schauinsland that channels the flow ofpolluted air from the city of Freiburg to the site.From the decay of hydrocarbons and NO_x between the twomeasuring sites and the known rate coefficients, theconcentration of OH radicals was calculated. From abudget analysis of OH and HO_x it is concluded that therelatively high OH concentrations (5–8 ×10⁶cm^-3) in the presence of high NO₂concentrations cannot be explained by the knownprimary sources. The budget can be closed if efficientrecycling of OH via HO₂ is assumed to occur andthat, based on the measured hydrocarbons, 2 HO₂molecules are formed for each OH radical that reactswith a hydrocarbon molecule. This assumption is inaccordance with the budget of O_x obtained from ourmeasurements and with results from earliermeasurements of alkylnitrates and peroxy radicals atSchauinsland. A possible conclusion is that the decayof precursors and production of photooxidants in urbanplumes proceeds at a faster rate than is currentlyassumed. The potential role of biogenichydrocarbons for the radical budget is alsodiscussed.     

Analysis of the Effect of Optical Properties of Black Carbon on Ozone in an Urban Environment at the Yangtze River Delta,China

Black carbon(BC) reduces the photolysis coefficient by absorbing solar radiation, thereby affecting the concentration of ozone(O_3) near the ground. The influence of BC on O_3 has thus received much attention. In this study, Mie scattering and the tropospheric Ultraviolet and Visible radiation model are used to analyze the effect of BC optical properties on radiation. Combined with data of O_3 precursors in Nanjing in 2014, an EKMA curve is drawn, and the variations in O_3 concentration are further investigated using a zero-dimensional box mechanism model(NCAR MM). When O_3 precursors are unchanged, radiation and O_3 show a highly similar tendency in response to changing BC optical properties(R=0.997).With the increase of modal radius, the attenuation of fresh BC to radiation and O_3 first trends upward before decreasing. In the mixing process, the attenuation of BC to radiation and O_3 presents an upward tendency with the increase of relative humidity but decreases rapidly before increasing slowly with increasing thickness of coating. In addition, mass concentration is another major factor. When the BC to PM2.5 ratio increases to 5% in Nanjing, the radiation decreases by approximately 0.13%–3.71% while O_3 decreases by approximately 8.13%–13.11%. The radiative effect of BC not only reduces O_3 concentration but also changes the EKMA curve. Compared with the NOx control area, radiation has a significant influence on the VOCs control area. When aerosol optical depth(AOD) increases by 17.15%, the NOx to VOCs ratio decreases by 8.27%, and part of the original NOx control area is transferred to the VOCs control area.     

A Wind-tunnel Study of Atmospheric Boundary-Layer Flow over Vegetated Surfaces to Suppress PM10 Emission on Owens (dry) Lake

Dust storms on Owens (dry) Lake located 200 milesnortheast of Los Angeles, California, U.S.A., havecaused serious PM₁₀ emission problems. Alaboratory-based experimental study was conducted toinvestigate the efficiency of 'vegetation cover' onthe playa to suppress dust emission rates as part ofa mitigation plan.Erodible lakebed material and field vegetation (saltgrass) taken from Owens (dry) Lake were placed in awind tunnel to simulate near-surface wind flow in theatmospheric boundary layer. Vertical wind-speedprofiles and vertical PM₁₀-concentration profileswere measured over six different levels of surfacevegetation cover. In order to understand the mechanismof aeolian particle transport and dust injection intothe atmosphere, the roughness parameter, z₀, thefriction velocity, u_*, and the surface dragcoefficient, C_D, were carefully determined.An empirical equation was developed to predictPM₁₀ emission rates as a function of wind speedand level of vegetation coverage for Owens (dry) Lake.Although the current results apply only to theeffectiveness of vegetation cover to suppressPM₁₀ emissions at Owens playa, the procedure canbe employed for any arid area or region that mightutilize added vegetation as a mitigation measure.     

大连地区能见度影响因子及个例分析

为探讨大连市大气能见度特征及其影响因子,揭示低能见度天气成因,利用2010—2012年大连地区大气能见度与地面气象要素(相对湿度、风速、气温、气压)日均值的统计资料,分析了大连地区大气能见度与气象要素的相关性。进一步结合PM_(10)质量浓度的变化特征,分析了两次低能见度事件中的天气成因。结果表明:2010—2012年大连地区年均能见度分别约为13.5 km、13.2 km和13.9 km,高能见度事件多出现在10月—次年2月,低能见度事件多出现在每年6—8月,大连地区低能见度事件每年7月较多,1月较少,2010—2012年大连地区低能见度事件分别出现169、157 d和163 d;2010—2012年PM_(10)质量浓度分别为57.8μg·m~(-3)、67.4μg·m~(-3)和65.9μg·m~(-3),PM_(10)质量浓度高值多出现在每年的4—5月和9—12月,PM_(10)质量浓度低值多出现在1—2月;大气能见度和相对湿度和气温的相关性较好,随着相对湿度的增加,能见度与PM_(10)质量浓度的相关性逐渐减小,当相对湿度大于90%时,能见度与PM_(10)质量浓度相关系数减小至-0.23;两次低能见度事件过程中,2011年10月31日一次辐射平流雾过程中的水汽输送来自西南风气流,2012年4月28日一次浮尘事件过程中的沙尘来自西北方向的沙源。该研究可为空气质量预报提供科学依据参考。     

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。     

On the Spatial Distribution and Seasonal Variation of Lower-Troposphere Ozone over Europe

Surface ozone data from 25 Europeanlow-altitude sites and mountain sites located between79°N and 28°N were studied. The analysiscovered the time period March 1989–February 1993.Average summer and winter O₃ concentrations inthe boundary layer over the continent gave rise togradients that were strongest in the north-west tosouth-east direction and west-east direction, respectively. WintertimeO₃ ranged from 19 to 27 ppbover the continent, compared to about 32 ppb at thewestern border, while for summer the continentalO₃ values ranged between 39 and 56 ppb and theoceanic mixing ratios were around 37 ppb. In the lowerfree troposphere average wintertime O₃ mixingratios were around 38 ppb, with only an 8 ppbdifference between 28°N and 79°N. For summerthe average O₃ levels decreased from about 55 ppbover Central Europe to 32 ppb at 79°N. Inaddition, O₃ and O_x(= O₃ + NO₂)in polluted and clean air were compared. Theamplitudes of the seasonal ozone variations increasedin the north-west to south-east direction, while thetime of the annual maximum was shifted from spring (atthe northerly sites) to late summer (at sites inAustria and Hungary), which reflected the contributionof photochemical ozone production in the lower partsof the troposphere.     

新冠肺炎疫情期间中国人为碳排放和大气污染物的变化

利用行业经济活动数据、1 580个地面监测站和6套卫星反演数据,分析了我国新冠肺炎疫情期间人为碳排放和主要大气污染物的变化。与2019年第一季度相比,2020年同期我国碳排放降低9.8%,其中交通部门降幅最大达到43.4%。与2019年2-3月相比,疫情期间全国地表臭氧浓度同比升高1.9 nL/L(5%),其中华北平原以降低为主,东南部地区以上升为主。PM2.5浓度同比下降12.6μg·m^-3(24.9%),其中长三角降幅最大。二氧化氮(NO2)的地面浓度和对流层柱浓度在京津冀、珠三角和长三角都降低20%~30%,体现了高低层的一致性。地面一氧化碳(CO)浓度同比降低17%,而对流层CO柱浓度升高2.5%,可能原因是境外生物质燃烧输送提升了我国南方高层大气的CO浓度。中东部地区气溶胶光学厚度显著降低,导致地表晴空短波辐射同比升高11.6 W·m^-2(9.6%)。     

A model investigation of the impact of increases in anthropogenic NO x emissions between 1967 and 1980 on tropospheric ozone

Recent observations suggest that the abundance of ozone between 2 and 8 km in the Northern Hemisphere mid-latitudes has increased by about 12% during the period from 1970 to 1981. Earlier estimates were somewhat more conservative suggesting increases at the rate of 7% per decade since the start of regular observations in 1967. Previous photochemical model studies have indicated that tropospheric ozone concentrations would increase with increases in emissions of CO, CH₄ and NO _x . This paper presents an analysis of tropospheric ozone which suggests that a significant portion of its increase may be attributed to the increase in global anthropogenic NO _x emissions during this period while the contribution of CH₄ to the increase is quite small. Two statistical models are presented for estimating annual global anthropogenic emissions of NO _x and are used to derive the trend in the emissions for the years 1966–1980. These show steady increase in the emissions during this interval except for brief periods of leveling off after 1973 and 1978. The impact of this increase in emissions on ozone is estimated by calculations with a onedimensional (latitudinal) model which includes coupled tropospheric photochemistry and diffusive meridional transport. Steady-state photochemical calculations with prescribed NO _x emissions appropriate for 1966 and 1980 indicate an ozone increase of 8–11% in the Northern Hemisphere, a result which is compatible with the rise in ozone suggested by the observations.     

Segregation and Interpretation of Ozone and Carbon Monoxide Measurements by Air Mass Origin at the TOR Station Mace Head, Ireland from 1987 to 1995

Three independent methods have been used to sort the ozone, carbonmonoxide, and other radiatively important trace gases measured at Mace Head,Ireland, and thereby distinguish clean air masses transported over the NorthAtlantic from the more polluted air masses which have recently travelledfrom the European continent. Over the period April 1987–June 1995 theNorthern Hemisphere surface ozone baseline concentrations exhibited a meanconcentration of 34.8 ppb, with a small positive trend (+0.19 ppbyr^-1), while the corresponding trend in air originating fromthe polluted European areas was negative (–0.39 ppbyr^-1). Carbon monoxide measurements from March 1990 toDecember 1994 showed negative trends for both the unpolluted (–0.17ppb yr^-1) and polluted data (–13.6 ppbyr^-1). Overall the continent of Europe was shown to be a smallnet sink of 2.6 ppb for all occasions when European air was transported tothe North Atlantic.     

Extreme Particulate Levels at a Western Pacific Coastal City: The Influence of Meteorological Factors and the Contribution of Long-Range Transport

The 4-year data sets (1998–2001) of PM₁₀ and other gaseous pollutants at four rural and urban monitoring sites provided by Environmental Protection Department of Hong Kong have been analyzed for days of extremely high and low PM₁₀ levels. The annual means of PM₁₀ concentrations are between 37 and 57 μg/m³. The level of high PM₁₀ concentration is defined from the comparison of local and international standards. Episode days are mainly controlled by different meteorological conditions: the continental outflow, the land-sea breeze/weak synoptic forcings and the approaching tropical cyclones. Integrated approaches have been used to distinguish between the predominantly “territory wide” and “long-range transport” (LRT) episode days. Case studies of these types of episodes are presented and the number of episode days per year for each type has been estimated. It is found that the LRT contributions are significant and account for ∼66% of the PM₁₀ episode days. Very high correlations between CO and PM₁₀ concentrations, and between SO₂ and PM₁₀ concentrations, can be found during the “territory wide” episode days which implies the important contributions of fossil fuel combustion to the PM₁₀ episodes. The number of “low level” PM₁₀ days per year has decreased by a factor near 3 from 1998 to 2001. Precipitation scavenging is the major process causing low levels of PM₁₀, irrespective of the associated weather systems. The regional annual background level is ∼9 μg/m³. With the exception of seasalt components, the average elemental concentrations of major inorganic species are similar for all of the sites during LRT events and constitute representative compositions of PM₁₀ during such events.     

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.     

Origin and source regions of PM10 in the Eastern Mediterranean atmosphere

A set of daily PM₁₀ (n = 281) samples collected from April 2001 to April 2002 at a rural site (Erdemli), located on the coast of the Eastern Mediterranean, were analyzed applying Mass Closure (MC), absolute principal factor analysis (APFA) and Positive Matrix Factorization (PMF) to determine source contributions. The results from the three techniques were compared to identify the similarities and differences in the sources and source contributions. Source apportionment analysis indicated that PM₁₀ were mainly originated from natural sources (sea salt + crustal ≈ 60%) whilst secondary aerosols and residual oil burning accounted for approximately 20% and 10% of the total PM₁₀ mass, respectively. Calculations for sulfate showed that on average 8% and 12% of its total concentration were originated from sea salt and biogenic emissions, respectively. However, the contribution by biogenic emissions may reach up to a maximum of ~ 40% in the summer. Potential Source Contribution Function (PSCF) analysis for identification of source regions showed that the Saharan desert was the main source area for crustal components. For secondary aerosol components the analysis revealed one source region, (i.e. the south-Eastern Black Sea), whereas for residual oil, Western Europe and the western Balkans areas were found to be the main source regions.     

Fourier transform infrared kinetic studies of the reaction of HONO with HNO3, NO3 and N2O5 at 295 K

The kinetics of the reaction of nitrous acid (HONO) with nitric acid (HNO₃), nitrate radicals (NO₃) and dinitrogen pentoxide (N₂O₅) have been studied using Fourier transform infrared spectroscopy. Experiments were performed at 700 torr total pressure using synthetic air or argon as diluents. From the observed decay of HONO in the presence of HNO₃ a rate constant of k<7×10^-19 cm³ molecule^-1 s^-1 was derived for the reaction of HONO with HNO₃. From the observed decay of HONO in the presence of mixtures of N₂O₅ and NO₂ we have also derived upper limits for the rate constants of the reactions of HONO with NO₃ and N₂O₅ of 2×10^-15 and 7×10^-19 cm³ molecule^-1 s^-1, respectively. These results are discussed with respect to previous studies and to the atmospheric chemistry of HONO.     

Seasonal variations of atmospheric sulfur dioxide and dimethylsulfide concentrations at Amsterdam Island in the southern Indian Ocean

Daily measurements of atmospheric sulfur dioxide (SO₂) concentrations were performed from March 1989 to January 1991 at Amsterdam Island (37°50 S–77°30 E), a remote site located in the southern Indian Ocean. Long-range transport of continental air masses was studied using Radon (²²²Rn) as continental tracer. Average monthly SO₂ concentrations range from less than 0.2 to 3.9 nmol m^-3 (annual average = 0.7 nmol m^-3) and present a seasonal cycle with a minimum in winter and a maximum in summer, similar to that described for atmospheric DMS concentrations measured during the same period. Clear diel correlation between atmospheric DMS and SO₂ concentrations is also observed during summer. A photochemical box model using measured atmospheric DMS concentrations as input data reproduces the seasonal variations in the measured atmospheric SO₂ concentrations within ±30%. Comparing between computed and measured SO₂ concentrations allowed us to estimate a yield of SO₂ from DMS oxidation of about 70%.     

A Study of DMS Oxidation in the Tropics: Comparison of Christmas Island Field Observations of DMS, SO2, and DMSO with Model Simulations

This study reports comparisonsbetween model simulations, based on current sulfurmechanisms, with the DMS, SO₂ and DMSOobservational data reported by Bandy et al.(1996) in their 1994 Christmas Island field study. For both DMS and SO₂, the model results werefound to be in excellent agreement with theobservations when the observations were filtered so asto establish a common meteorological environment. Thisfiltered DMS and SO₂ data encompassedapproximately half of the total sampled days. Basedon these composite profiles, it was shown thatoxidation of DMS via OH was the dominant pathway withno more than 5 to 15% proceeding through Cl atoms andless than 3% through NO₃. This analysis wasbased on an estimated DMS sea-to-air flux of 3.4 ×10⁹ molecs cm^-2 s^-1. The dominant sourceof BL SO₂ was oxidation of DMS, the overallconversion efficiency being evaluated at 0.65 ± 0.15. The major loss of SO₂ was deposition to theocean's surface and scavenging by aerosol. Theresulting combined first order k value was estimated at 1.6 × 10^-5 s^-1. In contrast to the DMSand SO₂ simulations, the model under-predictedthe observed DMSO levels by nearly a factor of 50. Although DMSO instrument measurement problems can notbe totally ruled out, the possibility of DMSO sourcesother than gas phase oxidation of DMS must beseriously considered and should be explored in futurestudies.     

A modified profile method for determining the vertical fluxes of NO,NO2, ozone,and HNO3 in the atmospheric surface layer

A modified profile method for determining the vertical deposition (or/and exhalation) fluxes of NO, NO₂, ozone, and HNO₃ in the atmospheric surface layer is presented. This method is based on the generally accepted micrometeorological ideas of the transfer of momentum, sensible heat and matter near the Earth's surface and the chemical reactions among these trace gases. The analysis (aerodynamic profile method) includes a detailed determination of the micrometeorological quantities (such as the friction velocity, the fluxes of sensible and latent heat, the roughness length and the zero plane displacement), and of the height-invariant fluxes of the composed chemically conservative trace gases with group concentrations c ₁=[NO]+[NO₂]+[HNO₃], c ₂=[NO₂]+[O₃]+3/2·[HNO₃], and c ₃=[NO]–[O₃]–1/2·[HNO₃]. The fluxes of the individual species are finally determined by the numerical solution of a system of coupled nonlinear ordinary differential equations for the concentrations of ozone and HNO₃ (decoding method). The parameterization of the fluxes is based on the flux-gradient relationships in the turbulent region of the atmospheric surface layer. The model requires only the vertical profile data of wind velocity, temperature and humidity and concentrations of NO, NO₂, ozone, and HNO₃.The method has been applied to vertical profile data obtained at Jülich (September 1984) and collected in the BIATEX joint field experiment LOVENOX (Halvergate, U.K., September 1989).