Determination of nitrogen dioxide, sulfur dioxide, ozone, and ammonia in ambient air using the passive sampling method associated with ion chromatographic and potentiometric analyses

Concentrations of nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3), and ammonia (NH3) were determined in the ambient air of Al-Ain city over a year using the passive sampling method associated with ion chromatographic and potentiometric detections. IVL samplers were used for collecting nitrogen and sulfur dioxides whereas Ogawa samplers were used for collecting ozone and ammonia. Five sites representing the industrial, traffic, commercial, residential, and background regions of the city were monitored in the course of this investigation. Year average concentrations of ≤59.26, 15.15, 17.03, and 11.88 μg/m3 were obtained for NO2, SO2, O3, and NH3, respectively. These values are lower than the maxima recommended for ambient air quality standards by the local environmental agency and the world health organization. Results obtained were correlated with the three meteorological parameters: humidity, wind speed, and temperature recorded during the same period of time using the paired t test, probability p values, and correlation coefficients. Humidity and wind speed showed insignificant effects on NO2, SO2, O3, and NH3 concentrations at 95% confidence level. Temperature showed insignificant effects on the concentrations of NO2 and NH3 while significant effects on SO2 and O3 were observed. Nonlinear correlations (R2 ≤ 0.722) were obtained for the changes in measured concentrations with changes in the three meteorological parameters. Passive samplers were shown to be not only precise (RSD ≤ 13.57) but also of low cost, low technical demand, and expediency in monitoring different locations

The FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data

The FLUXNET2015 dataset provides ecosystem-scale data on CO2, water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.Peer reviewe

Climate control of terrestrial carbon exchange across biomes and continents

Peer reviewe

Modelling net ecosystem carbon and water exchange of a temperate Eucalyptus delegatensis forest using multiple constraints

This study examined the carbon budget of a Eucalyptus delegatensis forest over four years under contrasting weather conditions by using a comprehensive forest-growth model (CenW 3.1). Model parameterisation was constrained through multiple measurements, including daytime eddy flux measurements of CO2 and water vapour exchange, estimates of above- and below-ground biomass pools, growth rates measured through stem-diameter increments and measurement of specific ecosystem processes, such as litter fall and soil respiration rates. The resultant estimates of net ecosystem exchange ranged from an uptake of 4.0 t C ha-1 year-1 in a year with adequate rainfall to a loss of 0.4 t C ha-1 year-1 in a year affected by drought and insect damage. The simulations indicated that this reduction in carbon gain was primarily due to insect damage rather than a direct consequence of water shortage. Under good growing conditions, carbon gain accumulated equally in stem wood and other biomass pools while soil organic carbon and woody litter were gradually decreasing following harvesting that had occurred 20 years earlier. Under more stressful conditions, net biomass increments decreased, while soil organic carbon and woody litter increased because of greater litter inputs and because drier conditions inhibited decomposition. Modelled estimates of photosynthesis and net ecosystem exchange were similar to estimates from eddy flux observations alone provided that it used a novel routine for deriving night-time carbon fluxes. Estimates of net ecosystem exchange derived in the present work were, however, substantially lower than previous estimates that had been derived using a more traditional analysis of eddy flux data. This study showed that detailed physiological modelling is a valuable technique for combining all available site information as well as further constraints based on broader scientific principles and considerations of the conservation of mass. It can thus provide a powerful constraint on the overall site carbon budget of an ecosystem

Multiple measurements constrain estimates of net carbon exchange by a Eucalyptus forest

Net ecosystem exchange of carbon (FNEE) was estimated for a temperate broadleaf, evergreen eucalypt forest ecosystem at Tumbarumba in south-eastern Australia to investigate the processes controlling forest carbon sinks and their response to climate. Measurements at a range of temporal and spatial scales were used to make three different estimates of FNEE based on: (1) the difference between fluxes of carbon input by photosynthesis and output by autotrophic plus heterotrophic respiration, (2) changes over time in the carbon pools in the above- and below-ground biomass, soil and litter, and (3) micrometeorological flux measurements that provide a continuous estimate of the net exchange. A rigorous comparison of aggregated component fluxes and the net eddy fluxes within a flux tower source area was achieved based on an inventory of the site and a detailed sampling strategy. Measurements replicated in space and time provided mean values, confidence limits and patterns of variation of carbon pools and fluxes that allowed comparisons within known limits of uncertainty. As a result of comparisons between nighttime eddy flux and chamber measurements of respiration, a revised micrometeorological method was developed for estimating nighttime carbon flux using flux tower measurements. Uncertainty in the final estimate of FNEE was reduced through mutual constraints of each of these measurement approaches. FNEE for the period October 2001-September 2002, with average rainfall, was an uptake of 6.7 (5.1-8.3) tC ha-1 yr-1 estimated from component fluxes, and 5.4 (3.0-7.5) tC ha-1 yr-1 estimated from the revised eddy flux method. Biomass increment was 4.5 (3.7-5.4) tC ha-1 yr-1 and the remaining 0.9-2.2 tC ha-1 yr-1 could represent a carbon sink in the soil and litter pools or lie within the confidence limits of the measured fluxes. FNEE was reduced to -0.1 to 2.4 tC ha-1 yr-1 during a period of drought and insect disturbance in October 2002-September 2003, with biomass increment being the main component reduced. The forest is a large carbon sink compared with other forest ecosystems, but this is subject to high-annual variability in response to climate variability and disturbance

Primary and secondary effects of climate variability on net ecosystem carbon exchange in an evergreen Eucalyptus forest

To understand the dynamics of ecosystem carbon cycling more than 10 years of eddy covariance data, measured over an evergreen, temperate, wet sclerophyll forest, were analysed and related to climate drivers on time scales ranging from hours to years. On

Estimating nocturnal ecosystem respiration from the vertical turbulent flux and change in storage of CO2

Micrometeorological measurements of night time ecosystem respiration can be systematically biased when stable atmospheric conditions lead to drainage flows associated with decoupling of air flow above and within plant canopies. The associated horizontal and vertical advective fluxes cannot be measured using instrumentation on the single towers typically used at micrometeorological sites. A common approach to minimize bias is to use a threshold in friction velocity, u*, to exclude periods when advection is assumed to be important, but this is problematic in situations when in-canopy flows are decoupled from the flow above. Using data from 25 flux stations in a wide variety of forest ecosystems globally, we examine the generality of a novel approach to estimating nocturnal respiration developed by van Gorsel et al. (van Gorsel, E., Leuning, R., Cleugh, H.A., Keith, H., Suni, T., 2007. Nocturnal carbon efflux: reconciliation of eddy covariance and chamber measurements using an alternative to the u*-threshold filtering technique. Tellus 59B, 397-403, Tellus, 59B, 307-403). The approach is based on the assumption that advection is small relative to the vertical turbulent flux (F-C) and change in storage (F-S) of CO2 in the few hours after sundown. The sum of F-C and F-S reach a maximum during this period which is used to derive a temperature response function for ecosystem respiration. Measured hourly soil temperatures are then used with this function to estimate respiration R-Rmax. The new approach yielded excellent agreement with (1) independent measurements using respiration chambers, (2) with estimates using ecosystem light-response curves of F-c + F-s extrapolated to zero light, R-LRC, and (3) with a detailed process-based forest ecosystem model, R-cast. At most sites respiration rates estimated using the u*-filter, R-ust, were smaller than R-Rmax, and R-LRC. Agreement of our approach with independent measurements indicates that R-Rmax, provides an excellent estimate of nighttime ecosystem respiration. (C) 2009 Elsevier B.V. All rights reserved