Jari Walden

CARBON BALANCE OF A BOREAL BOG DURING A YEAR WITH AN EXCEPTIONALLY DRY SUMMER

Northern peatlands are important terrestrial carbon stores, and they show large spatial and temporal variation in the atmospheric exchange of CO2 and CH4. Thus, annual carbon balance must be studied in detail in order to predict the climatic responses of these ecosystems. Closed-chamber methods were used to study CO2 and CH4 in hollow, Sphagnum angustifolium lawn, S. fuscum lawn, and hummock microsites within an om- brotrophic S. fuscum bog. Micrometeorological tower measurements were used as a ref- erence for the CH4 efflux from the bog. Low precipitation during May-August in 1994 (84 mm below the long-term average for the same period) and a warm July-August period caused the water table to drop by more than 15 cm below the peat surface in the hollows and to 48 cm below the surface in high hummocks. Increased annual total respiration exceeded gross production and resulted in a net C loss of 4-157 g/m2 in the different microsites. Drought probably caused irreversible desiccation in some lawns of S. angus- tifolium and S. balticum and in S. fuscum in the hummocks, while S. balticum growing in hollows retained its moisture and even increased its photosynthetic capacity during the July-August period. Seasonal (12 May-4 October) CH4 emissions ranged from 2 g CH4- C/M2 in drier S. fuscum hummocks and lawns to 7 and 14 g/m2 in wetter S. angustifolium- S. balticum lawns and hollows, respectively. Aerodynamic gradient measurements at the tower showed slightly higher CH4 flux rates than the average estimates for the whole bog obtained by closed-chamber methods. Winter C efflux comprised 30 g C02-C/m2 and 1 g CH4-C/m2 out of a total loss of 90 g C/M2 on average in the bog, and there was an estimated annual loss of 7 g C/M2 by leaching. This study shows how delicately the boreal bogs C balance in different microsites depends on climatic variations, especially the distribution of precipitation. It also confirms that severe C losses can occur in boreal bogs during extended summer droughts, even in years with annual temperatures close to the long-term average and with precipitation clearly greater than the long-term average.

A measurement campaign in a street canyon in Helsinki and comparison of results with predictions of the OSPM model

In 1997, a measuring campaign was conducted in a street canyon (Runeberg St.) in Helsinki. Hourly mean concentrations of CO, NOx, NO2 and O3 were measured at street and roof levels, the latter in order to determine the urban background concentrations. The relevant hourly meteorological parameters were measured at roof level; these included wind speed and direction, temperature and solar radiation. Hourly street level measurements and on-site electronic traffic counts were conducted throughout the whole of 1997; roof level measurements were conducted for approximately two months, from 3 March to 30 April in 1997. CO and NOx emissions from traffic were computed using measured hourly traffic volumes and evaluated emission factors. The Operational Street Pollution Model (OSPM) was used to calculate the street concentrations and the results were compared with the measurements. The overall agreement between measured and predicted concentrations was good for CO and NOx (fractional bias were −4.2 and +4.5%, respectively), but the model overpredicted the measured NO2 concentrations (fractional bias was +22%). The agreement between the measured and predicted values was also analysed in terms of its dependence on wind speed and direction; the latter analysis was performed separately for two categories of wind velocity. The model qualitatively reproduces the observed behaviour very well. The database, which contains all measured and predicted data, is available for further testing of other street canyon dispersion models. The dataset contains a larger proportion of low wind speed cases, compared with other available street canyon measurement datasets.

Evaluation of the OSPM model combined with an urban background model against the data measured in 1997 in Runeberg Street, Helsinki

Abstract In 1997, a measuring campaign was conducted in a street canyon (Runeberg Street) in Helsinki. Hourly street level measurements and on-site electronic traffic counts were conducted throughout the whole of 1997; roof level measurements were conducted for approximately two months during the so-called intensive measuring campaign, from 3 March to 30 April 1997. Hourly mean concentrations of NOx, NO2, O3 and CO were measured at street and roof levels; the relevant hourly meteorological parameters were measured at roof level. We present here an evaluation of the Operational Street Pollution Model (OSPM) street canyon dispersion model against the data measured during the whole of 1997. As the roof level concentrations and meteorological measurements were not available for the whole year, we utilised computed or meteorologically pre-processed values. The use of modelled urban background concentrations and meteorological values (instead of on-site roof level measurements) did not lessen the agreement between modelled and measured average concentration values at street level. The agreement between the temporal variations of predictions and measured data was also fairly good; for instance, the corresponding index of agreement values for NOx, NO2 and CO were 0.89, 0.81 and 0.87, respectively. However, as expected, the agreement in the temporal variations was somewhat better using actual measured on-site data during the intensive measuring campaign, than when using modelled urban background concentrations and meteorological values. This study demonstrates that it is possible to utilise the street canyon dispersion model OSPM with reasonable accuracy using modelled urban background and pre-processed meteorological values as model input.

Final report, on-going key comparison BIPM.QM-K1: Ozone at ambient level, comparison with FMI, 2007

As part of the on-going key comparison BIPM.QM-K1, a comparison has been performed between the ozone national standard of the Czech Hydrometeorological Institute (CHMI) and the common reference standard of the key comparison, maintained by the Bureau International des Poids et Mesures (BIPM). The instruments have been compared over a nominal ozone mole fraction range of 0 nmol/mol to 500 nmol/mol.

International Key Comparison CCQM-K26.b and Pilot Study CCQM-P50.b: Comparison of primary standards of sulphur dioxide (SO2) in synthetic air

Accurate measurements of sulphur dioxide at the concentrations found in ambient air have become essential to support monitoring and legislation concerned with air quality. In general, the primary element of quality assurance for field instruments is regular calibration using certified gas mixtures. The concentration range chosen for this Key Comparison (240 nmol/mol to 320 nmol/mol) is defined by appropriate European standards and is typical of similar levels used around the world. The travelling standards used for the comparison were prepared commercially by a supplier with a proven track record of preparing stable mixtures of the relevant gases. The coordinating laboratory (NPL) carried out stability checks on the mixtures and determined the amount fraction using a primary gravimetric permeation facility. These data were used to determine the drift rate (and uncertainty) of each standard. The results for the 11 participants in CCQM-K26.b and the one participant in CCQM-P50.b are presented in this report. Degrees of equivalence have been calculated based on a reference value (corresponding to the KCRV) derived from the primary gravimetric facility used by the coordinating laboratory. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Characteristics of Sulphur Dioxide Monitors: Intercomparison

The performance characteristics of five commercial sulphur dioxide monitors were studied. The experiments included both laboratory tests and field monitoring in an urban environment. According to the laboratory tests, the most sensitive concentration region was between 100 and 500 ppb [1 ppb(SO2) = 2.86 μgm−3 at NTP]. The lower detection limits were 2 to 5 ppb, and the precision varied from 1 to 26 ppb in the concentration range up to 500 ppb. The field data were analyzed with orthogonal regression and principal component analysis, and the results were less favourable than in the laboratory tests.

Final report on COOMET.QM-S1 (COOMET project no 483/RU/09): Supplementary comparison of primary standard gas mixtures: Nitrogen monoxide in nitrogen (50 µmol/mol)

Nitrogen monoxide is one of the main contaminants present in the atmospheric air due to emissions of vehicles and power stations. Taking into account the positive experience of VNIIM in the pilot study CCQM-P73 (Nitrogen monoxide gas standards, 30 ?mol/mol to 70 ?mol/mol), a COOMET project (No 483/RU/09) on the subject was decided and registered in the KCDB as supplementary comparison COOMET.QM-S1. This involved six National Metrology Institutes, aiming to consolidate or support their Calibration and Measurement Capabilities in this field. It was found that most of the results were consistent with the reference (gravimetric) values, with observed differences not exceeding ?1.3% and not exceeding either the appropriate assigned expanded uncertainties. There was, however, one exception: the INMETRO difference from the reference value is slightly higher than the expended uncertainty. The mixtures prepared for this exercise were found to be stable during about one year within the uncertainty of the measurements. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by COOMET, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

International comparison CCQM-K51: Carbon monoxide (CO) in nitrogen (5 µmol mol−1)

The first key comparison on carbon monoxide (CO) in nitrogen dates back to 1992 (CCQM-K1a). It was one of the first types of gas mixtures that were used in an international key comparison. Since then, numerous national metrology institutes (NMIs) have been setting up facilities for gas analysis, and have developed claims for their Calibration and Measurement Capabilities (CMCs) for these mixtures. Furthermore, in the April 2005 meeting of the CCQM (Consultative Committee for Amount of Substance) Gas Analysis Working Group, a policy was proposed to repeat key comparisons for stable mixtures every 10 years. This comparison was performed in line with the policy proposal and provided an opportunity for NMIs that could not participate in the previous comparison. NMISA from South Africa acted as the pilot laboratory. Of the 25 participating laboratories, 19 (76%) showed satisfactory degrees of equivalence to the gravimetric reference value. The results show that the CO concentration is not influenced by the measurement method used, and from this it may be concluded that the pure CO, used to prepare the gas mixtures, was not 13C-isotope depleted. This was confirmed by the isotope ratio analysis carried out by KRISS on a 1% mixture of CO in nitrogen, obtained from the NMISA. There is no indication of positive or negative bias in the gravimetric reference value, as the results from the different laboratories are evenly distributed on both sides of the key comparison reference value. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Final report of International Comparison EUROMET.QM-K1c: Comparison of measurements of nitrogen monoxide in nitrogen

Following-up the key comparison CCQM-K1c, EUROMET organized a regional key comparison involving ten laboratories. The objectives of this EUROMET key comparison were essentially the same as for the CCQM-K1c comparison: to compare the measurement capabilities of national metrological institutes (NMIs) in measuring amount of substance fractions of nitrogen monoxide in nitrogen. The nominal amount of substance fraction of the standards used for the comparison was 100 µmol/mol. The pilot laboratory in this key comparison also piloted the CCQM key comparison and has long-term experience in the behaviour of these mixtures and the technical challenges in preparing batches of very similar mixtures. Most participants used chemiluminescence as the measurement method; two participants used UV techniques and one ND-IR. The degrees of equivalence between this comparison and CCQM-K1c were calculated; four laboratories participated in both key comparisons, thus providing sufficient data for demonstrating the comparability. Main text. To reach the main text of this paper, click on Final Report. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the Mutual Recognition Arrangement (MRA).

Model Predictions on Urban Air Quality and Their Comparison to Measurements

We discuss studies on urban air quality in the Helsinki metropolitan area. This area includes four cities, which have a total population of 850 000. We have conducted comprehensive emission surveys comprising mobile and stationary sources, in 1990 and 1993. The emission time series were formed using the LIISA system, developed at the Technical Research Centre of Finland, and the transportation planning system EMME/2. The atmospheric dispersion was evaluated by the models UDM-FMI (The Urban Dispersion Modelling system of the FMI) and CAR-FMI (Contaminants in the Air from a Road) (Harkonen et al., 1994). Both dispersion models are connected to a meteorological preprocessing model, which is based on Monin-Obukhov type boundary layer scaling.