Frank Dentener

Global Biodiversity: Indicators of Recent Declines

Global Biodiversity Target Missed In 2002, the Convention on Biological Diversity (CBD) committed to a significant reduction in the rate of biodiversity loss by 2010. There has been widespread conjecture that this target has not been met. Butchart et al. (p. 1164, published online 29 April) analyzed over 30 indicators developed within the CBDs framework. These indicators include the condition or state of biodiversity (e.g., species numbers, population sizes), the pressures on biodiversity (e.g., deforestation), and the responses to maintain biodiversity (e.g., protected areas) and were assessed between about 1970 and 2005. Taken together, the results confirm that we have indeed failed to meet the 2010 targets. An analysis of 30 indicators shows that the Convention on Biological Diversity’s 2010 targets have not been met. In 2002, world leaders committed, through the Convention on Biological Diversity, to achieve a significant reduction in the rate of biodiversity loss by 2010. We compiled 31 indicators to report on progress toward this target. Most indicators of the state of biodiversity (covering species’ population trends, extinction risk, habitat extent and condition, and community composition) showed declines, with no significant recent reductions in rate, whereas indicators of pressures on biodiversity (including resource consumption, invasive alien species, nitrogen pollution, overexploitation, and climate change impacts) showed increases. Despite some local successes and increasing responses (including extent and biodiversity coverage of protected areas, sustainable forest management, policy responses to invasive alien species, and biodiversity-related aid), the rate of biodiversity loss does not appear to be slowing.

Role of mineral aerosol as a reactive surface in the global troposphere

A global three-dimensional model of the troposphere is used to simulate the sources, abundances, and sinks of mineral aerosol and the species involved in the photochemical oxidant, nitrogen, and sulfur cycles. Although the calculated heterogeneous removal rates on mineral aerosol are highly uncertain, mainly due to poorly known heterogeneous reaction rates, the reaction of SO2 on calcium-rich mineral aerosol is likely to play an important role downwind of arid source regions. This is especially important for regions in Asia, which are important and increasing emitters of sulfur compounds. Our results indicate that the assumption that sulfate aerosol follows an accumulation mode size distribution, is particularly in Asia likely to overestimate the sulfate aerosol climate-cooling effect. An even larger fraction of gas phase nitric acid may be associated with and neutralized by mineral aerosol. Interactions of N2O5, O3, and HO2-radicals with dust are calculated to affect the photochemical oxidant cycle, causing ozone decreases up to 10% in and nearby the dust source areas. Comparison of these results with limited available measurements indicates that the proposed reactions can indeed take place, although due to a lack of measurements a rigorous evaluation is not possible at this time.

Nitrogen and sulfur deposition on regional and global scales: A multimodel evaluation

We use 23 atmospheric chemistry transport models to calculate current and future (2030) deposition of reactive nitrogen (NOy, NHx) and sulfate (SOx) to land and ocean surfaces. The models are driven by three emission scenarios: (1) current air quality legislation (CLE); (2) an optimistic case of the maximum emissions reductions currently technologically feasible (MFR); and (3) the contrasting pessimistic IPCC SRES A2 scenario. An extensive evaluation of the present-day deposition using nearly all information on wet deposition available worldwide shows a good agreement with observations in Europe and North America, where 60–70% of the model-calculated wet deposition rates agree to within ±50% with quality-controlled measurements. Models systematically overestimate NHx deposition in South Asia, and underestimate NOy deposition in East Asia. We show that there are substantial differences among models for the removal mechanisms of NOy, NHx, and SOx, leading to ±1 σ variance in total deposition fluxes of about 30% in the anthropogenic emissions regions, and up to a factor of 2 outside. In all cases the mean model constructed from the ensemble calculations is among the best when comparing to measurements. Currently, 36–51% of all NOy, NHx, and SOx is deposited over the ocean, and 50–80% of the fraction of deposition on land falls on natural (nonagricultural) vegetation. Currently, 11% of the worlds natural vegetation receives nitrogen deposition in excess of the “critical load” threshold of 1000 mg(N) m−2 yr−1. The regions most affected are the United States (20% of vegetation), western Europe (30%), eastern Europe (80%), South Asia (60%), East Asia (40%), southeast Asia (30%), and Japan (50%). Future deposition fluxes are mainly driven by changes in emissions, and less importantly by changes in atmospheric chemistry and climate. The global fraction of vegetation exposed to nitrogen loads in excess of 1000 mg(N) m−2 yr−1 increases globally to 17% for CLE and 25% for A2. In MFR, the reductions in NOy are offset by further increases for NHx deposition. The regions most affected by exceedingly high nitrogen loads for CLE and A2 are Europe and Asia, but also parts of Africa.

A global high‐resolution emission inventory for ammonia

A global emissions inventory for ammonia (NH3) has been compiled for the main known sources on a 1° × 1° grid, suitable for input to global atmospheric models. The estimated global emission for 1990 is about 54 Tg N yr−1. The major sources identified include excreta from domestic animals (21.6 Tg N yr−1) and wild animals (0.1 Tg N yr−1), use of synthetic N fertilizers (9.0 Tg N yr−1), oceans (8.2 Tg N yr−1), biomass burning (5.9 Tg N yr−1), crops (3.6 Tg N yr−1), human population and pets (2.6 Tg N yr−1), soils under natural vegetation (2.4 Tg N yr−1), industrial processes (0.2 Tg N yr−1 ), and fossil fuels (0.1 Tg N yr−1). About half of the global emission comes from Asia, and about 70% is related to food production. The regions with highest emission rates are located in Europe, the Indian subcontinent, and China, reflecting the patterns of animal densities and type and intensity of synthetic fertilizer use. The overall uncertainty in the global emission estimate is 25%, while the uncertainty in regional emissions is much greater. As the global human population will show considerable growth in the coming decades, food production and associated NH3 emissions are likely to increase as well.

Impacts of Atmospheric Anthropogenic Nitrogen on the Open Ocean

Increasing quantities of atmospheric anthropogenic fixed nitrogen entering the open ocean could account for up to about a third of the oceans external (nonrecycled) nitrogen supply and up to ∼3% of the annual new marine biological production, ∼0.3 petagram of carbon per year. This input could account for the production of up to ∼1.6 teragrams of nitrous oxide (N2O) per year. Although ∼10% of the oceans drawdown of atmospheric anthropogenic carbon dioxide may result from this atmospheric nitrogen fertilization, leading to a decrease in radiative forcing, up to about two-thirds of this amount may be offset by the increase in N2O emissions. The effects of increasing atmospheric nitrogen deposition are expected to continue to grow in the future.

Reaction of N2O5 on tropospheric aerosols: Impact on the global distributions of NO x , O3, and OH

Using a three-dimensional global model of the troposphere, we show that the heterogeneous reactions of NO 3 and N205 on aerosol particles have a substantial influence on the concentrations of NOx; 03, and OH. Due to these reactions, the modeled yearly average global NOx burden decreases by 50% (80% in winter and 20% in summer). The heterogeneous removal of NOx in the northern hemisphere (NH) is dominated by reactions on aerosols; in the tropics and southern hemisphere (SH), with substantial smaller aerosol concentrations, liquid water clouds can provide an additional sink for N205 and NO 3. During spring in the NH subtropics and at mid-latitudes, O3-concentrations are lowered by 25%. In winter and spring in the subtropics of the NH calculated OH concentrations decreased by up to 30%. Global tropospheric average 03 and OH burden (the latter weighted with the amount of methane reacting with OH) can drop by about 9% each. By including reactions on aerosols, we are better able to simulate observed nitrate wet deposition patterns in North America and Europe. 03 concentrations in springtime smog situations are shown to be affected by heterogeneous reactions, indicating the great importance of chemical interactions resulting from NOx and SO2 emissions. However, a preliminary analysis shows that under present conditions a change in aerosol concentrations due to limited SO2 emission control strategies (e.g., reductions by a factor of 2 in industrial areas) will have only a relatively minor influence on 03 concentrations. Much larger reductions in SO2 emissions may cause larger increases in surface 03 concentrations, up to a maximum of 15%, if they are not accompanied by a reductio!a in NOx or hydrocarbon emission.

What controls tropospheric ozone

We have applied a global three-dimensional ort model to quantify the photochemistry of tropospheric O 3 and compare the main source categories. We simulated a 15 year period (1979-1993) on the basis of the European Centre for Medium-Range Weather Forecasts meteorological reanalyses and a time-varying emission data set. We calculate that stratosphere-troposphere exchange (STE) strongly contributes to 0 3 in regions where the photochemistry is quiescent. Since such regions play a minor role in radiative and chemical processes, we argue that STE-derived 0 3 is much less important than is suggested by its column abundance. By distinguishing between photochemical pathways in the model we calculate that tropospheric 0 3 in the extratropical Northern Hemisphere is strongly affected by industrial and fossil fuel-related emissions. In the tropics and Southern Hemisphere, natural emissions still play a major role. Our model results indicate a less important role for man-made biomass burning emissions than previous analyses. Further, the results show that tropospheric 03 trends are strongly influenced by transports of pollution and by meteorological variability. Scenario calculations for the year 2025 suggest that man-made emissions at low northern latitudes, in particular in southern and eastern Asia, will become a very strong tropospheric 0 3 source in the next decades. This will influence 0 3 levels on a hemispheric scale so that despite pollution regulations in Europe and North America, surface 0 3 will continue to grow. About 90% of atmospheric ozone is present in the strato- sphere, and only 10% is present in the troposphere. Despite this relatively small fraction, tropospheric ozone governs oxi- dation processes in the Earths atmosphere through the for- mation of hydroxyl (OH) radicals. OH, which controls the atmospheric lifetime of many gases, is formed by photodisso- ciation of 03 in the presence of water vapor (Levy, 1971):

A three-dimensional model of the global ammonia cycle.

Using a three-dimensional (3-D) transport model of the troposphere, we calculated the global distributions of ammonia (NH3) and ammonium (NH4+), taking into account removal of NH3 on acidic aerosols, in liquid water clouds and by reaction with OH. Our estimated global 10°×10° NH3 emission inventory of 45 Tg N-NH3 yr− provides a reasonable agreement between calculated wet NH4+ deposition and measurements and of measured and modeled NH4+ in aerosols, although in Africa and Asia especially discrepancies exist.NH3 emissions from natural continental ecosystems were calculated applying a canopy compensation point and oceanic NH3 emissions were related to those of DMS (dimethylsulfide). In many regions of the earth, the pH found in rain and cloud water can be attributed to acidity derived from NO, SO2 and DMS emissions and alkalinity from NH3. In the remote lower troposphere, sulfate aerosols are calculated to be almost neutralized to ammonium sulfate (NH4)2SO4, whereas in the middle and upper troposphere, according to our calculations, the aerosol should be more acidic, as a result of the oxidation of DMS and SO2 throughout the troposphere and removal of NH3 on acidic aerosols at lower heights. Although the removal of NH3 by reaction with the OH radical is relatively slow, the intermediate NH2 radical can provide a substantial annual N2O source of 0.9−0.4+0.9 Tg, thus contributing byca. 5% to estimated global N2O production. The oxidation by OH of NH3 from anthropogenic sources accounts for 10% of the estimated total anthropogenic sources of N2O. This source was not accounted for in previous studies, and is mainly located in the tropics, which have high NH3 and OH concentrations. Biomass burning plumes, containing high NOx and NH3 concentrations provide favourable conditions for gas phase N2O production. This source is probably underestimated in this model study, due to the coarse resolution of the 3-D model, and the rather low biomass burning NH3 and NOx emissions adopted. The estimate depends heavily on poorly known concentrations of NH3 (and NOx) in the tropics, and uncertainties in the rate constants of the reactions NH2 + NO2 → N2O + H2O (R4), and NH2 + O3 → NH2O + O2 (R7).

Contemporary and pre-industrial global reactive nitrogen budgets

Increases and expansion of anthropogenic emissions of both oxidized nitrogen compounds, NOx, and a reduced nitrogen compound, NH3, have driven an increase in nitrogen deposition. We estimate global NOx and NH3 emissions and use a model of the global troposphere, MOGUNTIA, to examine the pre-industrial and contemporary quantities and spatial patterns of wet and dry NOy and NHx deposition. Pre-industrial wet plus dry NOx and NHx deposition was greatest for tropical ecosystems, related to soil emissions, biomass burning and lightning emissions. Contemporary NOy+NHx wet and dry deposition onto Northern Hemisphere (NH) temperate ecosystems averages more than four times that of preindustrial N deposition and far exceeds contemporary tropical N deposition. All temperate and tropical biomes receive more N via deposition today than pre-industrially. Comparison of contemporary wet deposition model estimates to measurements of wet deposition reveal that modeled and measured wet deposition for both NO3− and NH4+ were quite similar over the U.S. Over Western Europe, the model tended to underestimate wet deposition of NO3− and NH4+ but bulk deposition measurements were comparable to modeled total deposition. For the U.S. and Western Europe, we also estimated N emission and deposition budgets. In the U.S., estimated emissions exceed interpolated total deposition by 3-6 Tg N, suggesting that substantial N is transported offshore and/or the remote and rural location of the sites may fail to capture the deposition of urban emissions. In Europe, by contrast, interpolated total N deposition balances estimated emissions within the uncertainty of each.

Exposure assessment for estimation of the global burden of disease attributable to outdoor air pollution.

Ambient air pollution is associated with numerous adverse health impacts. Previous assessments of global attributable disease burden have been limited to urban areas or by coarse spatial resolution of concentration estimates. Recent developments in remote sensing, global chemical-transport models, and improvements in coverage of surface measurements facilitate virtually complete spatially resolved global air pollutant concentration estimates. We combined these data to generate global estimates of long-term average ambient concentrations of fine particles (PM(2.5)) and ozone at 0.1° × 0.1° spatial resolution for 1990 and 2005. In 2005, 89% of the worlds population lived in areas where the World Health Organization Air Quality Guideline of 10 μg/m(3) PM(2.5) (annual average) was exceeded. Globally, 32% of the population lived in areas exceeding the WHO Level 1 Interim Target of 35 μg/m(3), driven by high proportions in East (76%) and South (26%) Asia. The highest seasonal ozone levels were found in North and Latin America, Europe, South and East Asia, and parts of Africa. Between 1990 and 2005 a 6% increase in global population-weighted PM(2.5) and a 1% decrease in global population-weighted ozone concentrations was apparent, highlighted by increased concentrations in East, South, and Southeast Asia and decreases in North America and Europe. Combined with spatially resolved population distributions, these estimates expand the evaluation of the global health burden associated with outdoor air pollution.