Diurnal fluxes of HONO above a crop rotation Laufs, Sebastian; Cazaunau, Mathieu; Stella, Patrick ...
Atmospheric chemistry and physics,
06/2017, Letnik:
17, Številka:
11
Journal Article
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Nitrous acid (HONO) fluxes were measured above an agricultural field site near Paris during different seasons. Above bare soil, different crops were measured using the aerodynamic gradient (AG) ...method. Two LOPAPs (LOng Path Absorption Photometer) were used to determine the HONO gradients between two heights. During daytime mainly positive HONO fluxes were observed, which showed strong correlation with the product of the NO2 concentration and the long wavelength UV light intensity, expressed by the photolysis frequency J(NO2). These results are consistent with HONO formation by photosensitized heterogeneous conversion of NO2 on soil surfaces as observed in recent laboratory studies. An additional influence of the soil temperature on the HONO flux can be explained by the temperature-dependent HONO adsorption on the soil surface. A parameterization of the HONO flux at this location with NO2 concentration, J(NO2), soil temperature and humidity fits reasonably well all flux observations at this location.
Croplands mainly act as net sources of the greenhouse gases carbon dioxide (CO2) and nitrous oxide (N2O), as well as nitrogen oxide (NO), a precursor of troposheric ozone. We determined the carbon ...(C) and nitrogen (N) balance of a four-year crop rotation, including maize, wheat, barley and mustard, to provide a base for exploring mitigation options of net emissions. The crop rotation had a positive net ecosystem production (NEP) of 4.4±0.7 Mg C ha-1 y-1 but represented a net source of carbon with a net biome production (NBP) of -1.3±1.1 Mg C ha-1 y-1. The nitrogen balance of the rotation was correlated with the carbon balance and resulted in net loss (–24±28 kg N ha-1 y-1). The main nitrogen losses were nitrate leaching (–11.7±1.0 kg N ha-1 y-1) and ammonia volatilization (–9 kg N ha-1 y-1). Dry and wet depositions were 6.7±3.0 and 5.9±0.1 kg N ha-1 y-1, respectively. Fluxes of nitrous (N2O) and nitric (NO) oxides did not contribute significantly to the N budget (N2O: -1.8±0.04; NO: -0.7±0.04 kg N ha-1 y-1) but N2O fluxes equaled 16% of the total greenhouse gas balance. The link between the carbon and nitrogen balances are discussed. Longer term experiments would be necessary to capture the trends in the carbon and nitrogen budgets within the variability of agricultural ecosystems.
Tropospheric ozone (O3) is probably the air pollutant most damaging to vegetation. Understanding how plants respond to O3 pollution under different climate conditions is of central importance for ...predicting the interactions between climate change, ozone impact and vegetation. This work analyses the effect of O3 fluxes on net ecosystem productivity (NEP), measured directly at the ecosystem level with the eddy covariance (EC) technique. The relationship was explored with artificial neural networks (ANNs), which were used to model NEP using environmental and phenological variables as inputs in addition to stomatal O3 uptake in Spring and Summer, when O3 pollution is expected to be highest. A sensitivity analysis allowed us to isolate the effect of O3, visualize the shape of the O3-NEP functional relationship and explore how climatic variables affect NEP response to O3. This approach has been applied to eleven ecosystems covering a range of climatic areas. The analysis highlighted that O3 effects over NEP are highly non-linear and site-specific. A significant but small NEP reduction was found during Spring in a Scottish shrubland (−0.67%), in two Italian forests (up to −1.37%) and during Summer in a Californian orange orchard (−1.25%). Although the overall seasonal effect of O3 on NEP was not found to be negative for the other sites, with episodic O3 detrimental effect still identified. These episodes were correlated with meteorological variables showing that O3 damage depends on weather conditions. By identifying O3 damage under field conditions and the environmental factors influencing to that damage, this work provides an insight into O3 pollution, climate and weather conditions.
This study investigated the impacts of extensive and semi-intensive green roofs on both building insulation and surface urban heat island effect under winter conditions. To this aim we compared ...measurements of surface and building envelope temperatures as well as conductive heat fluxes reaching the external building envelope with those measured on a conventional bituminous roof under identical climatic conditions. The main effect of green roofs was to decrease daily fluctuations of external building envelope temperatures and as a consequence to reduce fluctuations of conductive heat fluxes reaching the building envelope. This effect is all the more important that the substrate is deep, in link with its heat capacity and thermal inertia. Yet, no significant effect of the green roofs on surface urban heat island has been observed on average despite a surface cooling during daytime. It is concluded that the green roofs can be suitable urban greening solutions since they do not have negative effect on surface urban heat island during winter, provide cooling during summer, and contribute to building insulation inducing therefore building energy savings.
•Conventional, extensive and semi-intensive green roofs have been compared.•Green roofs reduced temperature and heat flux fluctuations at the building surface.•Deeper substrates reduced the temperature and heat flux fluctuations of the building surface.•On average there was no or only slight effects on winter surface urban heat island.
This study evaluates ozone (O3) deposition to an agricultural field over a period of 2 years. A two‐layer soil‐vegetation‐atmosphere‐transfer (Surfatm‐O3) model is used to partition the O3 flux ...between the soil, the cuticular, and the stomatal pathways. The comparison between measured and modeled O3 fluxes exhibited a good agreement, independently of the canopy structure and coverage and the climatic conditions, which implicitly validates the O3 flux partitioning. The total, soil, cuticular, and stomatal O3 budgets are then established from the modeling. Total ecosystem O3 deposition over the 2 year period was 87.5 kg ha−1. Clearly, nonstomatal deposition dominates the deposition budget, especially the soil component which represented up to 50% of the total deposition. Nevertheless, the physiological and phenological differences of maize and winter wheat induced large difference in the stomatal deposition budgets of these two crops. Then, the effect of simplified parameterizations for soil and cuticular resistances currently used in other models on the O3 budget is tested. Independently, these simplified parameterizations cause an underestimation of the O3 deposition ranging between 0% and 11.2%. However, the combination of all simplifications resulted in an underestimation of the total O3 deposition by about 20%. Finally, crop yield loss was estimated to be 1.5–4.2% for the winter wheat, whereas maize was not affected by O3.
Key Points
Total O3 deposition over the two‐year period was 87.5 kg ha‐1Soil removal accounted for 55.1% of the total O3 removalSimplified parameterizations underestimated O3 deposition by 20%
Surfatm is a two-layer resistance model to compute the exchanges of heat, water vapour, ammonia, ozone, and pesticides between the atmosphere, the vegetation, and the soil in several ecosystems at ...the field scale. After briefly describing its functioning and functionalities, some application studies using the model are presented. Surfatm is a tool suitable for research, decision-making, and lecturing activities in environmental sciences, specifically on heat, water, and pollutant exchanges between the atmosphere and the biosphere.
The atmosphere and the land surface interact in multiple ways, for instance through the radiative-energy balance, the water cycle or the emission and deposition of natural and anthropogenic ...compounds. By modifying the land surface, land use and land cover changes (LULCCs) and land management changes (LMCs) alter the physical, chemical, and biological processes of the biosphere and therefore all land-atmosphere interactions, from local to global scales. Through socio-economic drivers and regulatory policies adopted at different levels (local, regional, national, or supranational), human activities strongly interfere in the land-atmosphere interactions, and those activities lead to a patchwork of natural, semi-natural, agricultural, urban, and semi-urban areas. In this context, urban and peri-urban areas, which have a high population density, are of particular attention since land transformation can lead to important environmental impacts and affect the health and life of millions of people. The objectives of this review are to synthesize the existing experimental and modelling works that investigate physical, chemical, and/or biogeochemical interactions between land surfaces and the atmosphere, therefore potentially impacting local/regional climate and air quality, mainly in urban or peri-urban landscapes at regional and local scales.
Ozone is a potentially phyto-toxic air pollutant, which can cause leaf damage and drastically alter crop yields, causing serious economic losses around the world. The VULNOZ (VULNerability to OZone ...in Anthropised Ecosystems) project is a biology and modeling project that aims to understand how plants respond to the stress of high ozone concentrations, then use a set of models to (i) predict the impact of ozone on plant growth, (ii) represent ozone deposition fluxes to vegetation, and finally (iii) estimate the economic consequences of an increasing ozone background the future.
In this work, as part of the VULNOZ project, an innovative representation of ozone deposition to vegetation was developed and implemented in the CHIMERE regional chemistry-transport model. This type of model calculates the average amount of ozone deposited on a parcel each hour, as well as the integrated amount of ozone deposited to the surface at the regional or country level. Our new approach was based on a refinement of the representation of crop types in the model and the use of empirical parameters specific to each crop category. The results obtained were compared with a conventional ozone deposition modeling approach, and evaluated against observations from several agricultural areas in France. They showed that a better representation of the distribution between stomatal and non-stomatal ozone fluxes was obtained in the empirical approach, and they allowed us to produce a new estimate of the total amount of ozone deposited on the subtypes of vegetation at the national level.
•A new formulation of ozone deposition to crops and trees was implemented in the CHIMERE chemistry-transport model.•This work aimed at improving the representation of the dependency of O3 deposition to plants upon environmental parameters.•Based on field data, it provides a better representation of the stomatal/non-stomatal speciation of O3 fluxes to vegetation.•This topic remains a critical issue for the assessment of the impact of air pollution on the agricultural sector.
Soil deposition is an essential pathway for tropospheric ozone (O3) removal, but its controlling factors remain unclear. Here, we explored the variability of soil O3 resistance in response to soil ...texture. To this aim, data of O3 deposition over bare soil obtained from micrometeorological measurements under contrasted meteorological conditions for five sites were used. The results obtained are twofold: (i) soil resistance (Rsoil) increased with soil surface relative humidity (RHsurf), but (ii) this relationship exhibited large site-by-site variability. Further analysis showed that the minimum soil resistance (corresponding to completely dry soil surface or RHsurf = 0%) and the increase of Rsoil with RHsurf are both linked to soil clay content. These results can be explained by (i) the soil surface available for O3 deposition at a microscopic scale which is a function of the soil specific surface area, and (ii) the capacity of a soil to adsorb water according to its clay content and therefore to reduce the surface active for O3 deposition. From these results, a new parameterization has been established to estimate Rsoil as a function of RHsurf and soil clay fraction.
•Soil resistance to O3 deposition has been deduced for different kind of soils.•Soil resistance increases with surface relative humidity.•Parameters are dependent on soil clay content.•A new parameterization of soil resistance is proposed.
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