Spring Campaign Research Articles

Seasonal distributions of mercury species and their relationship to some physicochemical factors in Puding Reservoir, Guizhou, China

A comprehensive study was conducted in July 2006, January 2007 and March 2007 to determine the impacts of some major physicochemical parameters on the level of mercury (Hg) in Puding Reservoir, Guizhou, China. The concentrations of Hg species in the summer campaign were significantly higher ( p < 0.01, generally 2 to 3 times higher) than those in the winter and spring campaigns, and no statistical differences were found between the same parameters for the latter two campaigns ( p > 0.05). Ancillary parameters including suspended particulate matter (SPM), dissolved organic carbon (DOC), temperature (T), dissolved oxygen (DO), pH, nitrate (NO 3 −) and chloride (Cl −) were also measured. During the sampling campaign in July 2006, average values for SPM, DOC, T, and NO 3 − were all higher compared to the other two campaigns, which suggested a similar seasonal trend between these parameters and Hg species. Seasonal variability may be related to increased runoff. High runoff volume due to abundant precipitation in the summer carried Hg-laden particulates into the reservoir, whereas there was less precipitation in the winter and spring when Hg levels were lower. Increased agricultural activity in the summer season also increased Hg levels in Puding Reservoir.

Measurement of gas-phase total peroxides at the summit of Mount Tai in China

Measurement of ambient gas-phase total peroxides was performed at the summit of Mount Tai (Mt. Tai, 1534 m above sea level) in central-eastern China during March 22–April 24 and June 16–July 20, 2007. The hourly averaged concentration of peroxides was 0.17 ppbv (± 0.16 ppbv, maximum: 1.28 ppbv) and 0.55 ppbv (± 0.67 ppbv, maximum: 3.55 ppbv) in the spring and summer campaigns, respectively. The average concentration of peroxides at Mt. Tai, which is in a heavily polluted region, was much lower than hydrogen peroxide measurements made at some rural mountain sites, suggesting that significant removal processes took place in this region. An examination of diurnal variation and a correlation analysis suggest that these removal processes could include chemical suppression of peroxide production due to the scavenging of peroxy and hydroxy radicals by high NO x, wet removal by clouds/fogs rich in dissolved sulfur dioxide which reacts quickly with peroxides, and photolysis. These sinks competed with photochemical sources of peroxides, resulting in different mean concentrations and diurnal pattern of peroxides in the spring and summer. A principal component analysis was conducted to quantify the major processes that influenced the variation of peroxide concentrations. This analysis shows that in the spring photochemical production was an important source of peroxides, and the major sink was scavenging during upslope transport of polluted and humid air from the lower part of the planetary boundary layer (PBL) and wet removal by synoptic scale clouds. During the summer, highly polluted PBL air (with high NO x) was often associated with very low peroxides due to the chemical suppression of HO 2 by high NO x and wet-removal by clouds/fogs in this sulfur-rich atmosphere, especially during the daytime. Higher concentrations of peroxides, which often appeared at mid-nighttime, were mainly associated with subsidence of air masses containing relatively lower concentrations of NO y.

Using Aerosol Light Absorption Measurements for the Quantitative Determination of Wood Burning and Traffic Emission Contributions to Particulate Matter

A source apportionment study was performed for particulate matter in the small village of Roveredo, Switzerland, where more than 70% of the households use wood burning for heating purposes. A two-lane trans-Alpine highway passes through the village and contributes to the total aerosol burden in the area. The village is located in a steep Alpine valley characterized by strong and persistent temperature inversions during winter, especially from December to February. During two winter and one early spring campaigns, a seven-wavelength aethalometer, high volume (HIVOL) samplers, an Aerodyne quadrupole aerosol mass spectrometer (AMS), an optical particle counter (OPC), and a Sunset Laboratory OCEC analyzer were deployed to study the contribution of wood burning and traffic aerosols to particulate matter. A linear regression model of the carbonaceous particulate mass in the submicrometer size range CM(PM1) as a function of aerosol light absorption properties measured by the aethalometer is introduced to estimate the particulate mass from wood burning and traffic (PM(wb), PM(traffic)). This model was calibrated with analyses from the 14C method using HIVOL filter measurements. These results indicate that light absorption exponents of 1.1 for traffic and 1.8-1.9 for wood burning calculated from the light absorption at 470 and 950 nanometers should be used to obtain agreement of the two methods regarding the relative wood burning and traffic emission contributions to CM(PM1) and also to black carbon. The resulting PM(wb) and PM(traffic) values explain 86% of the variance of the CM(PM1) and contribute, on average, 88 and 12% to CM(PM1), respectively. The black carbon is estimated to be 51% due to wood burning and 49% due to traffic emissions. The average organic carbon/total carbon (OC/TC) values were estimated to be 0.52 for traffic and 0.88 for wood burning particulate emissions.

Benzene exposure in a sample of population residing in a district of Florence, Italy

Objective Personal exposure to airborne benzene is influenced by various outdoor and indoor sources. The first aim of this study was to assess the benzene exposure of a sample of urban inhabitants living in an inner-city neighborhood of Florence, Italy, excluding exposure from active smoking. The secondary objective was to differentiate the personal exposures according to personal usage patterns of the vehicles. Methods A sample of 67 healthy non-smokers was monitored by passive samplers during two 4-weekday campaigns in winter and late spring. Simultaneously, benzene measurements were also taken for a subset of participants, inside and outside their houses. A 4-day time microenvironment activity diary was completed by each subject during each sampling period. Other relevant exposure data were collected by a questionnaire before the sampling. Additional data on urban ambient air benzene levels were also available from the public air quality network. The passive samplers, after automated thermal desorption, were analyzed by GC-FID. Results Benzene personal exposure levels averaged 6.9 (SD = 2.1) and 2.3 (SD = 0.7) μg/m 3 in winter and spring, respectively. Outdoor and indoor levels showed high correlation in winter and poor in spring. In winter the highest benzene personal exposure levels were for people traveling by more public transport, followed by users of only car and by users of only bus respectively. Conclusions The time spent in-transport for work or leisure makes a major contribution to benzene exposure among Florentine non-smoking citizens. Indoor pollution and transportation means contribute significantly to individual exposure levels especially in winter season.

Nutrient Behavior in the Júcar Estuary and Plume

The Júcar River flows into Cullera Bay in the western Mediterranean Sea (Valencia, Spain). The river flow is over-exploited and usually has no significant discharge at the mouth, except during very rainy periods. As part of the ECOSUD project, nine sampling campaigns were carried out (June 2002–July 2003) at different stations and depths in the Júcar Estuary and Cullera Bay. This paper presents the nutrient analyses of two campaigns (summer and spring) with different weather conditions (without and with freshwater flow respectively). The results show that the freshwater layer of the river was higher in the spring campaign (April) than in the summer campaign (July), which resulted in a more evident freshwater influence at the marine stations near the river mouth. As expected, there was a general downward trend in the dissolved nutrient concentrations with lower river flow (lower continental influence). However, the variations observed were not always linear. With some exceptions, nutrient concentrations generally increased. Ammonium, SRP and orthosilicic acid increased due to the senescence, death and subsequent mineralization of freshwater organisms as salinity increased. Nitrate and nitrite also increased somewhat due to the nitrification of the ammonium. However, nitrite showed some losses in summer conditions (July) related to the different speeds of the two nitrification steps.

Benthic response to shellfish farming in Thau lagoon: Pore water signature

Vertical distributions of dissolved species across the sediment–water interface (SWI), including major cations (sodium, potassium, magnesium, calcium), minor cations (lithium, strontium, barium), redox sensitive species (dissolved manganese, iron, sulfate, sulfide, ammonium) and other chemical parameters (pH, alkalinity, soluble reactive phosphorous, dissolved silica) were studied in a Mediterranean lagoon used for intensive shellfish farming. In order to quantify the impact of this activity on diagenetic processes and the influence of seasonal changes, two stations contrasted with respect to organic carbon fluxes were sampled in Thau lagoon from March 2001 to August 2002 during four field campaigns in winter, spring, summer and fall. Well-defined layers enriched with redox sensitive species were observed following the conventional sequence of early diagenetic reactions. However, differences were observed between both stations in depths and thickness layers. Concentration gradients extended down to more than 92 cm depth at the central position of the lagoon (station C4 – 8 m depth) and down to 40 cm depth inside shellfish farming zones (station C5 – 9 m depth). Station C4 showed an unusual diagenetic signature: sharp dissolved oxygen, iron, nitrate and manganese gradients existed at the SWI but gradients of dissolved sulfide and alkalinity as well as other parameters (dissolved silica, Ba, etc.) were recorded only from 25 to 30 cm depth downward. Seasonal changes were observed in pore water composition as deep as 30–50 cm in station C4 (only 15 cm in station C5). The center of the lagoon is not directly subjected to biodeposits deriving from shellfish activity. Isotopic and bioturbation data allowed to rule out a reworking of the sediment deeper than a few centimeters. In addition to organic content of the sediment, physical parameters were likely to induce the 10–20 cm gap between dissolved iron and sulfide profile as well as the higher vertical extent of diagenetic sequence observed at station C4. Conversely to station C5, station C4 underwent stronger currents and wave effect probably generating advective transport of water through the sediment, but no permeability data were available to confirm this hypothesis. During summer, climatic conditions generated vertical stratification of the water column and transient suboxic conditions at the bottom. Such conditions drove the upward shift of redox fronts, compacting the diagenetic sequence. These effects were reinforced at station C5 by shellfish and its farm structures (mainly attenuation of current and increased heat absorption).

Spatial and temporal distribution of blackflies (Diptera: Simuliidae) in the Itatiaia National Park, Brazil

The distribution of the blackfly larval taxocenoses of different altitudes in the Itatiaia National Park (located in the southeast of Rio de Janeiro state, Brazil 44 degrees 34' - 44 degrees 42' W, 22 degrees 16' - 22 degrees 28' S) was investigated on four campaigns, one in each season of 2003. On each campaign 60 samples were collected, using 30 x 30 cm wooden quadrats, distributed at four sites: Taquaral, Véu da Noiva, Três Picos and Brejo da Lapa. The winter and spring campaigns included two additional sampling sites: Alsene and Agulhas Negras. A total of 3578 larvae and 292 pupae were sampled, representative of six species: Simulium clavibranchium Lutz, S. subnigrum Lutz, S. rappae Py-Daniel, S. incrustatum Lutz, S. stellatum Gil-Azevedo, Figueiró & Maia-Herzog and Lutzsimulium pernigrum Lutz 1910. The highest larvae abundance and diversity were reported at the intermediate altitude site, Brejo da Lapa. Principal Components Analysis (PCA) revealed that L. pernigrum, S. stellatum and S. incrustatum were associated with the smaller breeding sites, the first two species being associated with sunny sites, while S. incrustatum occurred in sites with little sunlight.

N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O, NO and CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; exchange, and microbial N turnover over a Mediterranean pine forest soil

Abstract. Trace gas exchange of N2O, NO/NO2 and CH4 between soil and the atmosphere was measured in a typical Mediterranean pine (Pinus pinaster) forest during two intensive field campaigns in spring and autumn 2003. Furthermore, gross and net turnover rates of N mineralization and nitrification as well as soil profiles of N2O and CH4 concentrations were determined. For both seasons a weak but significant N2O uptake from the atmosphere into the soil was observed. During the unusually dry and hot spring mean N2O uptake was −4.32 µg N m-2 h-1, whereas during the wet and mild autumn mean N2O uptake was −7.85 µg N m-2 h-1. The observed N2O uptake into the soil was linked to the very low availability of inorganic nitrogen at the study site. Organic layer gross N mineralization decreased from 5.06 mg N kg-1 SDW d-1 in springtime to 2.68 mg N kg-1 SDW d-1 in autumn. Mean NO emission rates were significantly higher in springtime (9.94 µg N m-2 h-1) than in autumn (1.43 µg N m-2 h-1). A significant positive correlation between NO emission rates and gross N mineralization as well as nitrification rates was found. The negative correlation between NO emissions and soil moisture was explained with a stimulation of aerobic NO uptake under N limiting conditions. Since NO2 deposition was continuously higher than NO emission rates the examined forest soil functioned as a net NOx sink. Observed mean net CH4 uptake rates were in spring significantly higher (−73.34 µg C m-2 h-1) than in autumn (−59.67 µg C m-2 h-1). Changes in CH4 uptake rates were strongly negatively correlated with changes in soil moisture. The N2O and CH4 concentrations in different soil depths revealed the organic layer and the upper 0.1 m of mineral soil as the most important soil horizons for N2O and CH4 consumption.

Chemical composition and mass closure of particulate matter at six urban sites in Europe

The chemical composition of fine (PM 2.5) and coarse (PM 2.5−10) particulate matter was investigated in 7-week field campaigns of contrasting air pollution at six urban background sites in Europe. The campaigns were scheduled to include seasons of local public health concern due to high particulate concentrations or findings in previously conducted epidemiological studies. The sampling campaigns were carried out as follows: Duisburg/Germany October–November 2002 (autumn), Prague/Czech Republic November 2002–January 2003 (winter), Amsterdam/Netherlands January–March 2003 (winter), Helsinki/Finland March–May 2003 (spring), Barcelona/Spain March–May 2003 (spring) and Athens/Greece June–July 2003 (summer). Aerosol samples were collected in 3+4-day periods per week ( N=14) using two identical virtual impactors (VI). All the filter samples were analysed with the same instruments to obtain particulate mass, inorganic ions, total and watersoluble elements, and elemental and organic carbon content. The campaign means of PM 2.5 and PM 2.5−10 ranged from 8.3 to 30 and 5.4 to 29 μg m −3, respectively. The “wet and cool” seasons favoured a low coarse-to-fine particulate mass ratio (<1), whereas the ratio was high (>1) during the warmer and drier spring and summer campaigns. According to chemical mass closure, the major components in PM 2.5 were carbonaceous compounds (organic matter+elemental carbon), secondary inorganic ions and sea salt, whereas those in PM 2.5−10 were soil-derived compounds, carbonaceous compounds, sea salt and nitrate. The major and minor components together accounted for 79–106% and 77–96% of the gravimetrically measured PM 2.5 and PM 2.5−10 mass, respectively. In conclusion, the measured PM 2.5 and PM 2.5−10 in the campaigns could be reconstructed to a large extent with the help of harmonized particulate sampling and analysis of the selected chemical constituents. The health significance of the observed differences in chemical composition and emission sources between the size-segregated particulate samples will be investigated in toxicological cell and animal studies.

The Papers of George Washington. Revolutionary War Series. Volume 14: March-April 1778 (review)

The Papers of George Washington. Revolutionary War Series. Volume 14: March-April 1778. Edited by Philander D. Chase. (Charlottesville: University of Virginia Press, 2004. Pp. 832. Cloth, $75.00.)Like clockwork, a new and welcome volume of The Papers of George Washington appears annually. And every year academics and general readers alike can count on the best scholarship possible. In the latest installment of Washington's Revolutionary War papers, that is just what they get. This volume covers March and April 1778, when Washington and the Continental army continued their long winter encampment at Valley Forge. With this volume the editors reveal General Washington and his army's day-to-day camp operations, his plan for the spring campaign, and his efforts to free prisoners of war, as well as the general's personal life.The opening of this volume finds Washington holding his band of troops together while preparing for the upcoming military season. The general confronted the most basic and serious problems while attempting to keep his troops from deserting. By death and desertion, Washington writes, have lost a good many men since we came to this ground, and have encountered every species of hardship that cold, wet, & hunger, arid want of Cloaths were capable of producg-not withstandg & contrary to my expectations we have been able to keep the Soldiers from Mutiny or dispersion (234). This is the Washington of lore, holding together the Continental force during its hour of trial.Holding the troops together became Washington's moral and practical duty, and the reader comes to understand their devotion to him. Yet this volume also demonstrates Washington's devotion to administrative leadership. This becomes clear in the issue of prisoner exchange between American and British forces. In the spring of 1778 both sides desired the release of their soldiers from the enemy's prisons. Washington wanted and needed his imprisoned troops, yet he broke off negotiations when he concluded that American officers were suffering indignities at the hands of General William Howe. In particular, Washington grew increasingly angry at the treatment of captured American General Charles Lee. Promises of Lee's release proved to be disingenuous, and Washington repaid in kind by refusing to release British Colonel Archibald Campbell, writing that his action was a consequence of your discrimination to the prejudice of General Lee (159). Both officers were released in April 1778, yet further negotiations were stymied over the issue of treatment of ranking officers. This is Washington, hard as nails, refusing to budge regardless of his weaker position.Although the military-minded Washington dominates this volume, hints of the private man emerge from these pages. A revealing example is in the letters of Lund Washington, Mount Vernon's manager and the general's cousin. When Lund planned a sale of Mount Vernon's slaves, the general interceded. Lund wrote, with regard to Sellg the Negroes Mention'd, you have put it out of my power, by saying you would not sell them without their Consent (429). This is the principled Washington. Washington was not an abolitionist by any means, but we can faintly make out the man who eventually will arrange his slaves' freedom. …

Prediction of indoor concentration of 0.5–4μm particles of outdoor origin in an uninhabited apartment

Indoor and outdoor particle size distributions, indoor–outdoor pressure difference, indoor air-exchange rate, and meteorological conditions were measured at an uninhabited apartment located in a busy street in Copenhagen during 1-month long fall, winter and spring campaigns. Particle penetration was estimated from concentration rebound measurements following HEPA filtering of the indoor air by fitting a simple deterministic model. The model included measured air exchange rates and published surface deposition loss rates. This model was then used to predict indoor particle concentration. The model predicted well the indoor concentration of coarse (1.2–4 μm) particles of outdoor origin for the fall and spring campaign. The model performed less well for the fine (0.5–1.2 μm) particle concentration and the winter campaign. The association between the ratio measured/predicted indoor concentration and factors not included in the deterministic model was analysed statistically and the result was used to determine a correction factor to the model prediction. The correction factor was found to depend on wind velocity, outdoor relative humidity, and air exchange rate. Including the correction factor reduced the ratio of the 95 percentile to the 5 percentile by an average of 26% for the fine particles and 12% for the coarse particles. The ratio measured/predicted concentration using the correction factor was found to be the highest during periods where it was most likely that occupants were present in other apartments. The results suggest that factors such as particle chemical composition, within building transport patterns, and occupant behaviour in other apartments should be identified and quantified in future studies, and that these factors need to be included in predictive models.

Receptor modeling of ambient VOC at Santiago, Chile

Ambient VOC measured at a 1996 spring campaign at Santiago, Chile, have been analyzed using the receptor models UNMIX and Positive Matrix Factorization (PMF). The ambient campaign took place at two sites: a downtown site, close to major traffic emissions, and a residential site, downwind of major industrial sources and highways. At the downtown site the following source apportionments estimates were obtained: fuel evaporation, 29.775.6%; gasoline exhaust, 22.073.4%; diesel exhaust, 18.172.9%; biogenic, LPG and evaporative emissions, 18.073.4%, unexplained: 12%. At the residential site, the following source apportionment was obtained: transported gasoline exhaust, 31.274.1%; local gasoline exhaust, 25.574.0%; evaporative losses, 11.772.8%; LPG losses, 11.072.5%; biogenic emissions, 7.771.7%; diesel exhaust, 6.271.5%; unexplained, 7.7%. Thus, near 70% of ambient VOC impacts at both sites are due to mobile sources. The receptor analyses produced source profiles that had distinctive, dominant compounds; in addition, source contributions exhibited diurnal profiles that were consistent with ambient temperature and wind speed data, and the expected activity patterns within the city. Typical errors in the source contributions vary between 15% for the larger sources—like gasoline exhaust—and 25% for the smaller sources—like biogenic emissions. It was found that the number of factors given by the UNMIX model was a good starting point to refine the solution using PMF. Both models showed good performance at discriminating between source profiles that had similar compositions in subsets of common species, but PMF was able to find better, cleaner source profiles that did UNMIX. At both monitoring sites LPG losses appear mixed in with other source profiles, and this feature could not be solved by adding more source profiles in the analyses; this was likely due to a lack of C3 measurements needed to better resolve an LPG source profile. r 2004 Elsevier Ltd. All rights reserved.

Denuder measurements of gas and aerosol species above Arctic snow surfaces at Alert 2000

Gas and aerosol measurements were made during the Polar Sunrise Experiment 2000 at Alert, Nunavut (Canada), using two independent denuder/filter systems for sampling and subsequent analysis by ion chromatography. Twelve to forty-eight hour samples were taken during a winter (9–21 February 2000) and a spring (17 April–5 May 2000) campaign. During the spring campaign, samples were taken at two different heights above the snow surface to investigate concentration differences. Total particulate NO 3 − is the most abundant inorganic nitrogen compound during Arctic springtime (mean 137.4 ng m −3). The NO 3 − fluxes were calculated above the snow surface to help identify processes that control snow–atmosphere exchange of reactive nitrogen compounds. We suggest that the observed fluxes of coarse particle NO 3 − via snow deposition may contribute to the nitrogen inventory in the snow surface. Measurements of surface snow provide experimental data that constrain the contribution of dry deposition of coarse particle NO 3 − to <7%. Wet deposition in falling snow appears to be the major contributor to the nitrate input to the snow.

Retrieval of the ultraviolet aerosol optical depth during a spring campaign in the Bavarian Alps

A measurement campaign was organized in March 1999 in the Bavarian Alps as part of the European project, Characteristics of the UV Radiation Field in the Alps (CUVRA), to analyze the effect of altitude, aerosols, and snow cover on ground-level UV spectral irradiance. We present the results of simultaneous measurements of aerosol optical depth (AOD) made at various sites on two cloudless days in March 1999. The two days exhibited different aerosol conditions. Results derived from spectral measurements of UV irradiance are compared with data from filter radiometer measurements made at discrete wavelengths extending from the UV to the near IR. The different methods generated values for the AOD that were in good agreement. This result confirms that one can use either method to retrieve the AOD with an uncertainty of approximately 0.03-0.05. On 18 March, high turbidity was observed at low altitude (400-nm AOD approximately 0.5 at 700 m above sea level), and the AOD decreased regularly with altitude; on 24 March, the turbidity was much less (0.11 at 700 m above sea level). On both days very low AODs (0.05-0.09) were measured at 3000 m above sea level. The spectral dependence of the AOD is often parameterized by the angstrom relationship; the alpha parameter is generally difficult or impossible to retrieve from spectral measurements because of the relatively narrow wavelength range (320-400 nm), and only one of the spectro-radiometers used during the campaign permits this retrieval. In most cases, during this field campaign, alpha was found by filter sunphotometers to be 1.1-1.5.

Formaldehyde in Arctic snow. Incorporation into ice particles and evolution in the snowpack

Formaldehyde was measured in the seasonal snowpack near Alert (Ellesmere Island 82.5°N, 62.3°W) during both winter and spring campaigns of ALERT2000. The time evolution of formaldehyde (HCHO) concentrations in fresh snow was monitored. Since snow metamorphism induces evaporation and condensation of both ice and its solutes, the evolution of snow microphysics was also studied. Simultaneous monitoring of the partial pressures of HCHO allowed the estimation of the partitioning of HCHO between the snowpack and the atmosphere. Assuming exchange layer thicknesses of 300 and 14 m during winter and spring, respectively, we calculated that over 80% of the total amount of HCHO in the (exchange layer+snow) system was in the snowpack. Snow is thus an important potential source of HCHO to the atmosphere. The mechanism of incorporation of HCHO in snow crystals must be known to understand its kinetics of exchange with the atmosphere. Tests were performed to determine whether HCHO was adsorbed on the ice surface, or dissolved in the ice crystalline lattice.

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],NOx (NO + NO2) and NOy (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.

Effects of continental boundary layer evolution, convection, turbulence and entrainment, on aerosol formation

Aerosol nucleation events occurring in the continental boundary layer over the boreal forest region in Finland, during the BIOFOR experiment, have been examined to elucidate the rôle of micrometeorology in promoting such events. Invariably, during the spring campaign of 1999, nucleation events occurred in Arctic and polar air masses during cold air outbreaks. Under clear-sky conditions, typical of these synoptic meteorological patterns, the boundary layer evolution was characterized by the rapid growth of a mixed layer, convection and strong entrainment, first from the residual later and later from the free troposphere. It was found that the freshly nucleated particles were detected within two hours from the onset of strong turbulent kinetic energy, independent of how fast the boundary layer evolved. When considering the growth time from cluster size of = 1 nm to detectable sizes of 3 nm, the nucleation and onset of strong turbulence coincided almost exactly. The most likely site for nucleation to take place was the mixed layer or the entrainment zone, while the forest canopy and the free troposphere could be excluded as the nucleation region. There are several possible explanations for the correlation between the onset of turbulence and nucleation: (1) new aerosols or clusters may have been entrained from the residual layer into the mixed layer where they then (in the case of clusters) underwent growth to detectable sizes; (2) two or more precursor gases may have been mixed with each other over the entrainment zone; (3) the adiabatic cooling in the rising convective plumes and the turbulent fluctuation in temperature and vapors by the entrainment flux may have enhanced aerosol formation; (4) a sudden decrease in preexisting aerosol due to dilution of the mixed layer aerosol by entrained air may have reduced the vapor sink enough to initiate nucleation. However, the lack of vertical profile measurements of nucleation mode aerosols, precursor vapors and turbulent fluctuations throughout and above the mixed-layer results in it remaining an open question as to which one of these processes dominates.

Emission fluxes and atmospheric degradation of monoterpenes above a boreal forest: field measurements and modelling

The contribution of monoterpenes to aerosol formation processes within and above forests is not well understood. This is also true for the particle formation events observed during the BIOFOR campaigns in Hyytiälä, Finland. Therefore, the diurnal variation of the concentrations of several biogenic volatile organic compounds (BVOCs) and selected oxidation products in the gas and particle phase were measured on selected days during the campaigns in Hyytiälä, Finland. α-pinene and Δ3-carene were found to represent the most important monoterpenes above the boreal forest. A clear vertical gradient of their concentrations was observed together with a change of the relative monoterpene composition with height. Based on concentration profile measurements of monoterpenes, their fluxes above the forest canopy were calculated using the gradient approach. Most of the time, the BVOC fluxes show a clear diurnal variation with a maximum around noon. The highest fluxes were observed for α-pinene with values up to 20 ng m−2 s−1 in summer time and almost 100 ng m−2 s−1 during the spring campaign. Furthermore, the main oxidation products from α-pinene, pinonaldehyde, and from β-pinene, nopinone, were detected in the atmosphere above the forest. In addition to these more volatile oxidation products, pinic and pinonic acid were identified in the particle phase in a concentration range between 1 and 4 ng m−3. Beside these direct measurement of known oxidation products, the chemical sink term in the flux calculations was used to estimate the amount of product formation of the major terpenes (α-pinene, β-pinene, Δ3-carene). A production rate of very low volatile oxidation products (e.g., multifunctional carboxylic) from ·OH- and O3-reaction of monoterpenes of about 1.3·104 molecules cm−3 s−1 was estimated for daylight conditions during summer time. Additionally, model calculations with the one-dimensional multilayer model CACHE were carried out to investigate the diurnal course of BVOC fluxes and chemical degradation of terpenes.

Effects of continental boundary layer evolution, convection, turbulence and entrainment, on aerosol formation

Aerosol nucleation events occurring in the continental boundary layer over the boreal forest region in Finland, during the BIOFOR experiment, have been examined to elucidate the rôle of micrometeorology in promoting such events. Invariably, during the spring campaign of 1999, nucleation events occurred in Arctic and polar air masses during cold air outbreaks. Under clear-sky conditions, typical of these synoptic meteorological patterns, the boundary layer evolution was characterized by the rapid growth of a mixed layer, convection and strong entrainment, first from the residual later and later from the free troposphere. It was found that the freshly nucleated particles were detected within two hours from the onset of strong turbulent kinetic energy, independent of how fast the boundary layer evolved. When considering the growth time from cluster size of = 1 nm to detectable sizes of 3 nm, the nucleation and onset of strong turbulence coincided almost exactly. The most likely site for nucleation to take place was the mixed layer or the entrainment zone, while the forest canopy and the free troposphere could be excluded as the nucleation region. There are several possible explanations for the correlation between the onset of turbulence and nucleation: (1) new aerosols or clusters may have been entrained from the residual layer into the mixed layer where they then (in the case of clusters) underwent growth to detectable sizes; (2) two or more precursor gases may have been mixed with each other over the entrainment zone; (3) the adiabatic cooling in the rising convective plumes and the turbulent fluctuation in temperature and vapors by the entrainment flux may have enhanced aerosol formation; (4) a sudden decrease in preexisting aerosol due to dilution of the mixed layer aerosol by entrained air may have reduced the vapor sink enough to initiate nucleation. However, the lack of vertical profile measurements of nucleation mode aerosols, precursor vapors and turbulent fluctuations throughout and above the mixed-layer results in it remaining an open question as to which one of these processes dominates.

Exchange of matter and energy between the Wadden Sea and the coastal waters of the German Bight-Estimations based on numerical simulations and field measurements

Based on numerical simulations and high resolution measurements, budgets have been computed for transports of water and heat as well as dissolved and particulate matter between the coastal waters of the German Bight and the North Frisian Wadden Sea. p]During 3 measuring campaigns in summer, spring and winter, current conditions and water transports differed only slightly. In spite of different meteorological situations, inflow and outflow of North Sea water to and from the Wadden Sea were largely balanced. A net heat export from the North Frisian Wadden Sea was determined both in summer 1994 and spring 1995, i. e. the Wadden Sea represented a heat source for the adjacent North Sea waters.