Accounting for Field-Scale Dry Deposition in Backward Lagrangian Stochastic Dispersion Modelling of NH3 Emissions
A controlled ammonia (NH3) release experiment was performed at a grassland site. The aim was to quantify the effect of dry deposition between the source and the receptors (NH3 measurement locations) on emission rate estimates by means of inverse dispersion modelling. NH3 was released for three hours at a constant rate of Q = 6.29 mg s−1 from a grid of 36 orifices spread over an area of 250 m2. The increase in line-integrated NH3 concentration was measured with open-path optical miniDOAS devices at different locations downwind of the artificial source. Using a backward Lagrangian stochastic (bLS) dispersion model (bLSmodelR), the fraction of the modelled release rate to the emitted NH3 ( Q bLS / Q ) was calculated from the measurements of the individual instruments. Q bLS / Q was found to be systematically lower than 1, on average between 0.69 and 0.91, depending on the location of the receptor. We hypothesized that NH3 dry deposition to grass and soil surfaces was the main factor responsible for the observed depletion of NH3 between source and receptor. A dry deposition algorithm based on a deposition velocity approach was included in the bLS modelling. Model deposition velocities were evaluated from a ‘big-leaf’ canopy resistance analogy. Canopy resistances (generally termed R c ) that provided Q bLS / Q = 1 ranged from 75 to 290 s m−1, showing that surface removal of NH3 by dry deposition can plausibly explain the original underestimation of Q bLS / Q . The inclusion of a dry deposition process in dispersion modelling is crucial for emission estimates, which are based on concentration measurements of depositing tracers downwind of homogeneous area sources or heterogeneously-distributed hot spots, such as, e.g., urine patches on pastures in the case of NH3.
Comparison of backward Lagrangian stochastic model with micrometeorological mass balance method for measuring ammonia emissions from rice field
Abstract A field experiment was conducted to assess the accuracy of the backward Lagrangian stochastic (BLS) model combined with an open-path tunable diode laser (OPTDL) system for estimating ammonia emissions from rice field by comparing with the micrometeorological mass balance (MMB) method. During the experimental period, the average height of rice was 0.65 m, and the average height of laser path was 1.3 m. The results showed that there was no significant difference between the ammonia emission rates estimated by the two methods, indicating no significant effect of tall rice on the accuracy of the BLS model. The high temporal resolution data showed that ammonia emissions had a dramatic diurnal cycle: rise at daytime and fall at night. Although the OPTDL technique was not able to measure ammonia concentrations at low emission rates due to relatively high detection limit, the total ammonia loss estimated by the BLS model was not significant different from that of the MMB method. The results demonstrate the effectiveness of the BLS model with the OPTDL technique for estimating ammonia emissions from farmland covered with tall vegetation. Within the acceptable accuracy, the relatively low laser path height is recommended for farmland with tall vegetation due to relatively high detection limit of the OPTDL technique and low ammonia concentration of farmland.
Genetic Effects of Acute and Chronic Ionizing Irradiation on Pinus sylvestrisL. Inhabiting the Chernobyl Meltdown Area
The main results of the 12-year radiation-genetic monitoring of radiobiological, cytogenetic, and genetic parameters in Pinus sylvestrisforest plantation from the Chernobyl meltdown area are presented. The acute ionizing irradiation at doses > 1 Gy was shown to induce formation of morphoses and depressed growth; at doses >2 Gy, the reproductive ability of the trees declined. The radiobiological parameters showed a linear or close to linear dose-dependence relationship. The acute irradiation at a dose of 0.5 Gy induced cytogenetic and genetic effects that were significantly higher than the corresponding control values. The relationship between the cytogenetic effects and the absorbed dose was exponential. The dependence of the mutation frequency at specific loci on the absorbed dose was described by a nonlinear curve. The results of cytogenetic analysis of seedlings obtained from seeds annually collected in zones of slight, moderate, and strong damage of Pinus sylvestrisL. are presented.