Simulated global climate response to tropospheric ozone-induced changes in plant transpiration

Tropospheric ozone (O₃) pollution is known to damage vegetation, reducing photosynthesis and stomatal conductance, resulting in modified plant transpiration to the atmosphere. We use an Earth system model to show that global transpiration response to near‐present‐day surface tropospheric ozone results in large‐scale global perturbations to net outgoing long‐wave and incoming shortwave radiation. Our results suggest that the radiative effect is dominated by a reduction in shortwave cloud forcing in polluted regions, in response to ozone‐induced reduction in land‐atmosphere moisture flux and atmospheric humidity. We simulate a statistically significant response of annual surface air temperature of up to ~ +1.5 K due to this ozone effect in vegetated regions subjected to ozone pollution. This mechanism is expected to further increase the net warming resulting from historic and future increases in tropospheric ozone

Lattice Boltzmann method for the fractional advection-diffusion equation

Mass transport, such as movement of phosphorus in soils and solutes in rivers, is a natural phenomenon and its study plays an important role in science and engineering. It is found that there are numerous practical diffusion phenomena that do not obey the classical advection-diffusion equation (ADE). Such diffusion is called abnormal or superdiffusion, and it is well described using a fractional advection-diffusion equation (FADE). The FADE finds a wide range of applications in various areas with great potential for studying complex mass transport in real hydrological systems. However, solution to the FADE is difficult, and the existing numerical methods are complicated and inefficient. In this study, a fresh lattice Boltzmann method is developed for solving the fractional advection-diffusion equation (LabFADE). The FADE is transformed into an equation similar to an advection-diffusion equation and solved using the lattice Boltzmann method. The LabFADE has all the advantages of the conventional lattice Boltzmann method and avoids a complex solution procedure, unlike other existing numerical methods. The method has been validated through simulations of several benchmark tests: a point-source diffusion, a boundary-value problem of steady diffusion, and an initial-boundary-value problem of unsteady diffusion with the coexistence of source and sink terms. In addition, by including the effects of the skewness β , the fractional order α , and the single relaxation time τ , the accuracy and convergence of the method have been assessed. The numerical predictions are compared with the analytical solutions, and they indicate that the method is second-order accurate. The method presented will allow the FADE to be more widely applied to complex mass transport problems in science and engineering

The Mediterranean summertime ozone maximum: Global emission sensitivities and radiative impacts

The Mediterranean troposphere exhibits a marked and localised summertime ozone maximum, which has the potential to strongly impact regional air quality and radiative forcing. The Mediterranean region can be perturbed by long-range pollution import from Northern Europe, North America and Asia, in addition to local emissions, which may all contribute to regional ozone enhancements. We exploit ozone profile observations from the Tropospheric Emission Spectrometer (TES) and the Global Ozone Monitoring Experiment-2 (GOME-2) satellite instruments, and an offline 3-D global chemical transport model (TOMCAT) to investigate the geographical and vertical structure of the summertime tropospheric ozone maximum over the Mediterranean region. We show that both TES and GOME-2 are able to detect enhanced levels of ozone in the lower troposphere over the region during the summer. These observations, together with surface measurements, are used to evaluate the TOMCAT model's ability to capture the observed ozone enhancement. The model is used to quantify sensitivities of the ozone maximum to anthropogenic and natural volatile organic compound (VOC) emissions, anthropogenic NOx emissions, wildfire emissions and long-range import of ozone and precursors. Our results show a dominant sensitivity to natural VOC emissions in the Mediterranean basin over anthropogenic VOC emissions. However, local anthropogenic NOx emissions are result in the overall largest sensitivity in near-surface ozone. We also show that in the lower troposphere, global VOC emissions account for 40% of the ozone sensitivity to VOC emissions in the region, whereas, for NOx the ozone sensitivity to local sources is 9 times greater than that for global emissions at these altitudes. However, in the mid and upper troposphere ozone is most sensitive to non-local emission sources. In terms of radiative effects on regional climate, ozone contributions from non-local emission sources are more important, as these have a larger impact on ozone in the upper troposphere where its radiative effects are larger, with Asian monsoon outflow having the greatest impact. Our results allow improved understanding of the large-scale processes controlling air quality and climate in the region of the Mediterranean basin

Intercontinental trans-boundary contributions to ozone-induced crop yield losses in the Northern Hemisphere

Using a global atmospheric chemistry model, we have quantified for the first time, intercontinental transboundary contributions to crop ozone exposure and subsequent yield reductions in the Northern Hemisphere. We apply four metrics (AOT40, M7, M12, W126) to assess the impacts of 100% reductions in anthropogenic NOx emissions from North (N) America, South East (SE) Asia and Europe on global and regional exposure of 6 major agricultural crop types to surface ozone, and resultant crop production losses during the year 2000 growing season. Using these metrics, model calculations show that for wheat, rice, cotton and potato, 100 % reductions in SE Asian anthropogenic NOx emissions tend to produce the greatest global reduction in crop production losses (42.3–95.2%), and a 100 % reduction to N~American anthropogenic NOx emissions results in the greatest global impact on crop production losses for maize and soybean (59.2–85.9%). A 100% reduction in N~American anthropogenic NOx emissions produces the largest transboundary impact, resulting in European production loss reductions of between 14.2% and 63.2%. European NOx emissions tend to produce a smaller transboundary impact, due to inefficiency of transport from the European domain. The threshold nature of the AOT40 ozone-exposure metric results in strong dependence of non-local emissions impacts on the local ozone concentration distribution. Our calculations of absolute crop production change under emission reduction scenarios differ between the metrics used, however we find the relative importance of each region's transboundary impact remains robust between metrics. Our results demonstrate that local air quality and emission control strategies have the potential to partly alleviate ozone-induced crop yield loss in continents downstream, in addition to effectively mitigating local ozone-induced production losses