For base year 2010, anthropogenic activities created ~210 (190 to 230) TgN of reactive nitrogen Nr from N2. This human-caused creation of reactive nitrogen in 2010 is at least 2 times larger than the rate of natural terrestrial creation of ~58 TgN (50 to 100 TgN yr−1) (Table 6.9, Section 1a). Note that the estimate of natural terrestrial biological fixation (58 TgN yr−1) is lower than former estimates (100 TgN yr−1, Galloway et al., 2004), but the ranges overlap, 50 to 100 TgN yr−1 vs. 90 to 120 TgN yr−1, respectively). Of this created reactive nitrogen, NOx and NH3 emissions from anthropogenic sources are about fourfold greater than natural emissions (Table 6.9, Section 1b). A greater portion of the NH3 emissions is deposited to the continents rather than to the oceans, relative to the deposition of NOy, due to the longer atmospheric residence time of the latter. These deposition estimates are lower limits, as they do not include organic nitrogen species. New model and measurement information (Kanakidou et al., 2012) suggests that incomplete inclusion of emissions and atmospheric chemistry of reduced and oxidized organic nitrogen components in current models may lead to systematic underestimates of total global reactive nitrogen deposition by up to 35% (Table 6.9, Section 1c). Discharge of reactive nitrogen to the coastal oceans is ~45 TgN yr−1 (Table 6.9, Section 1d). Denitrification converts Nr back to atmospheric N2. The current estimate for the production of atmospheric N2 is 110 TgN yr−1 (Bouwman et al., 2013).

/pdf/carbon-and-other-biogeochemical-cycles-3abybm74qt.pdf

Carbon and Other Biogeochemical Cycles

We present new estimates of global nitrous oxide (N2O) emissions for the period 1500–1994 based on revised Intergovernmental Panel on Climate Change guidelines [Intergovernmental Panel on Climate Change (IPCC), 1997; Mosier et al., 1998]. Use of these estimates as input to a simple atmospheric box model resulted in a closed N2O budget over time, showing that increases in atmospheric N2O can be primarily attributed to changes in food production systems. We hypothesize that before the ninetheenth century conversion of natural land to agriculture had no net effect on N2O. During the twentieth century a fast expansion of agricultural land coupled with intensification of land use may have caused a net increase in N2O. In our base scenario the total N2O emissions increased from 11 Tg N yr−1 in 1850 to 15 Tg N yr−1 in 1970 and to 18 Tg N yr−1 in 1994.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1998GB900020

Closing the global N2O budget: A retrospective analysis 1500–1994

A class of isotope effects that alters isotope ratios on a mass-independent basis provides a tool for studying a wide range of processes in atmospheres of Earth and other planets as well as early processes in the solar nebula. The mechanism for the effect remains uncertain. Mass-independent isotopic compositions have been observed in O3, CO2, N2O, and CO in Earth's atmosphere and in carbonate from a martian meteorite, which suggests a role for mass-independent processes in the atmosphere of Mars. Observed mass-independent meteoritic oxygen and sulfur isotopic compositions may derive from chemical processes in the presolar nebula, and their distributions could provide insight into early solar system evolution.

https://science.sciencemag.org/content/sci/283/5400/341.full.pdf

Mass-independent isotope effects in planetary atmospheres and the early solar system.

Inventories with 1°×1° resolution were compiled of nitrous oxide (N2O) emissions from fertilized arable land, animal excreta, postclearing effects on soil emissions, fossil fuel and fuelwood combustion, and industrial N2O sources. For other sources of N2O, including soils under natural vegetation, oceans, and biomass burning, published inventories were used. From these inventories the annual N2O emission was calculated for four broad latitudinal zones covering the globe. Uncertainties were assessed by comparing variants of inventories with source estimates inferred from inverse modeling techniques. Major uncertainties occur in the tropics, where small errors in both soil and oceanic emission estimates may have large repercussions for the zonal distributions. Although there may still be many poorly known and unidentified N2O sources, the analysis has resulted in improved understanding of some sources, i.e., (1) the oceanic N2O emission may be more important than assumed in recent global N2O budgets, with a major portion stemming from the 30°–90°S zone; (2) the N2O emission from animal excreta forms a significant global source; (3) most of the N2O from arable lands and grasslands, including effects of synthetic fertilizers and animal excreta, comes from the northern hemisphere; accounting for only the synthetic-fertilizer effect on N2O emission leads to an underestimation of the emission from arable lands; (4) fossil fuel combustion and industrial N2O sources are dominant in the 30°–90°N zone, while N2O from fuelwood combustion is mainly produced in the 0°–30°N zone; (5) the estimation of enhanced N2O soil emission following tropical forest clearing that has accounted for gradually declining N2O fluxes, along with aging of the clearing leads to a global emission that is significant but lower than previous estimates; (6) most of the N2O from coastal marine and freshwater systems and soil N2O emission resulting from N deposition probably comes from the northern hemisphere.

Uncertainties in the global source distribution of nitrous oxide

We present an overview of state-of-the-art chemistry–climate and chemistry transport models that are used within phase 1 of the Chemistry–Climate Model Initia- tive (CCMI-1). The CCMI aims to conduct a detailed evalua- tion of participating models using process-oriented diagnos- tics derived from observations in order to gain confidence in the models’ projections of the stratospheric ozone layer, tro- pospheric composition, air quality, where applicable global climate change, and the interactions between them. Interpre- tation of these diagnostics requires detailed knowledge of the radiative, chemical, dynamical, and physical processes incor- porated in the models. Also an understanding of the degree to which CCMI-1 recommendations for simulations have been followed is necessary to understand model responses to an- thropogenic and natural forcing and also to explain inter- model differences. This becomes even more important given the ongoing development and the ever-growing complexity of these models. This paper also provides an overview of the available CCMI-1 simulations with the aim of informing CCMI data users.

/pdf/review-of-the-global-models-used-within-phase-1-of-the-3qz1w58fo6.pdf

Review of the global models used within phase 1 of the Chemistry–Climate Model Initiative (CCMI)

An accurate line-by-line model is used to evaluate effects of absorption in the Schumann-Runge bands of O2 on transmission of UV radiation. The model is used to evaluate rates of photolysis for N2O, CFCl3, and CF2Cl2, and to infer global loss rates and instantaneous lifetimes appropriate for 1980. A parameterized version of the line-by-line model enabling rapid evaluation of transmission in the Schumann-Runge region is described. Photochemical calculations employing the parameterization and constrained by data from the Atmospheric Trace Molecule Spectroscopy experiment are used to examine the budget of odd oxygen. Consistent with previous studies, it is shown that photochemical loss of odd oxygen exceeds production by photolysis of O2 for altitudes above 40 km. The imbalance between production and loss is shown to be consistent with a source of odd oxygen proportional to the product of the mixing ratio and photolysis rate of ozone, which suggests that processes involving vibrationally excited O2 may play an important role in production of odd oxygen.

K. Minschwaner

Papers

Absorption of solar radiation by O2 - Implications for O3 and lifetimes of N2O, CFCl3, and CF2Cl2