Determining the spatial and temporal distribution of terrestrial gross primary production (GPP) is a critical step in closing the Earth's carbon budget. Dynamical global vegetation models (DGVMs) ...provide mechanistic insight into GPP variability but diverge in predicting the response to climate in poorly investigated regions. Recent advances in the remote sensing of solar‐induced chlorophyll fluorescence (SIF) opens up a new possibility to provide direct global observational constraints for GPP. Here, we apply an optimal estimation approach to infer the global distribution of GPP from an ensemble of eight DGVMs constrained by global measurements of SIF from the Greenhouse Gases Observing SATellite (GOSAT). These estimates are compared to flux tower data in N. America, Europe, and tropical S. America, with careful consideration of scale differences between models, GOSAT, and flux towers. Assimilation of GOSAT SIF with DGVMs causes a redistribution of global productivity from northern latitudes to the tropics of 7–8 Pg C yr⁻¹ from 2010 to 2012, with reduced GPP in northern forests (~3.6 Pg C yr⁻¹) and enhanced GPP in tropical forests (~3.7 Pg C yr⁻¹). This leads to improvements in the structure of the seasonal cycle, including earlier dry season GPP loss and enhanced peak‐to‐trough GPP in tropical forests within the Amazon Basin and reduced growing season length in northern croplands and deciduous forests. Uncertainty in predicted GPP (estimated from the spread of DGVMs) is reduced by 40–70% during peak productivity suggesting the assimilation of GOSAT SIF with models is well‐suited for benchmarking. We conclude that satellite fluorescence augurs a new opportunity to quantify the GPP response to climate drivers and the potential to constrain predictions of carbon cycle evolution.
Ground and satellite observations show that air pollution regulations in the United States (US) have resulted in substantial reductions in emissions and corresponding improvements in air quality over ...the last several decades. However, large uncertainties remain in evaluating how recent regulations affect different emission sectors and pollutant trends. Here we show a significant slowdown in decreasing US emissions of nitrogen oxides (NOₓ) and carbon monoxide (CO) for 2011–2015 using satellite and surface measurements. This observed slowdown in emission reductions is significantly different from the trend expected using US Environmental Protection Agency (EPA) bottom-up inventories and impedes compliance with local and federal agency air-quality goals. We find that the difference between observations and EPA’s NOₓ emission estimates could be explained by: (i) growing relative contributions of industrial, area, and off-road sources, (ii) decreasing relative contributions of on-road gasoline, and (iii) slower than expected decreases in on-road diesel emissions.
We conducted experiments with an atmospheric general circulation model to determine the effects of non‐Rayleigh, postcondensation exchange (PCE) on the isotopic composition of water in the ...atmosphere. PCE was found to universally deplete vapor of heavy isotopes but had differential effects on the isotopic composition of precipitation. At low latitudes, local PCE with fresh vapor at the surface enriches precipitation in heavy isotopes, particularly during light rainfall. When rainfall is heavy, PCE tends to deplete vapor and precipitation of heavy isotopes via atmospheric moisture recycling, supporting recent interpretations of vapor isotope measurements from satellites, particularly over the Asian Monsoon region. In the extratropics, PCE causes local enrichment of precipitation, which is often entirely offset by upstream PCE depletion of the source vapor, resulting in a net depletion in local precipitation. The transition from net enrichment to net depletion is controlled by the transition from rain to snow‐dominated precipitation. Surprisingly, this transition was also found to influence the temperature effect. In regions with a strong seasonal mix of rain and snow, such as Europe, the temperature effect appears to be controlled by PCE rather than Rayleigh depletion.
Ozone export from East Asia: The role of PAN Jiang, Zhe; Worden, John R.; Payne, Vivienne H. ...
Journal of geophysical research. Atmospheres,
16 June 2016, Volume:
121, Issue:
11
Journal Article
Peer reviewed
Open access
Peroxyacetyl nitrate (PAN) is an important ozone (O3) precursor. The lifetime of PAN is approximately 1 month in the free troposphere, and this allows O3 production to occur in pollution plumes at ...intercontinental distances from its source. In this study we use the Goddard Earth Observing System (GEOS)‐Chem global chemical transport model, new satellite measurements of PAN from the Aura Tropospheric Emission Spectrometer (TES), and data from the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) field campaign over North America, to study the role of natural and anthropogenic Asian emissions on free tropospheric (900–400 hPa) PAN distributions and subsequent O3 production. Using the ARCTAS data with GEOS‐Chem, we show that while GEOS‐Chem is unbiased with respect to the aircraft data, TES version 7 PAN data are biased high for regions with surface temperatures colder than 285 K. However, GEOS‐Chem and TES measurements provide a consistent representation (within 15% difference) of PAN abundance over East Asia. Because of the good agreement between model and observations, we use the GEOS‐Chem model to evaluate the sources of PAN precursors and the effect of free tropospheric PAN on the export of O3 from Asia to North America. The GEOS‐Chem model results show that the largest contributors to free tropospheric PAN over Asia and the northern Pacific are anthropogenic and soil NOx emissions. Biomass burning emissions have important contributions to free tropospheric PAN over northern Pacific (25% in April), while the contribution from lightning over northern Pacific is significant in July (40%). Strong springtime transport in April results in more export of free tropospheric PAN and O3 from East Asian emissions. This free tropospheric PAN contributes about 35% to the abundance of free tropospheric O3 over western North America in spring and 25% in summer.
Key Points
Agreement between model and TES PAN measurements
Anthropogenic and soil NOx are the major sources of Asian free tropospheric PAN
Important contribution (about 30%) of PAN on transpacific O3 transport
Observational data indicate increasing trends of surface ozone (O3) in China, despite emission controls that have resulted in reductions of precursor emissions. Here, we explore the cause of this ...contradiction, through analysis of surface observations (2014–2019) in China and historical observation record in the United States (US, 1990–2019). Our observation‐based analysis indicates that the reductions of nitrogen oxides (NOx) emissions led to increase of surface O3 in North China Plain (NCP) and Yangtze River Delta (YRD) of around 8 ppb. However, NOx controls resulted in shift of O3 chemical regimes over NCP and YRD, with turning points between NOx‐ and volatile organic compound (VOC)‐limited regimes around 2019, while model simulations suggest transitional or NOx‐limited regimes over the rest of China. The impacts of high fine particles (PM2.5) on O3 formation has declined because of the reduction of PM2.5 concentrations. Stricter NOx controls can mitigate O3 pollutions over industrialized areas in China.
Plain Language Summary
Ozone (O3) in surface air is an important pollutant with adverse effects on human health and vegetation growth. Here, we explore the sustainable pathway to control O3 pollution in China through analysis of observations in China (2014–2019) and the United States (US, 1990–2019). We find that the reductions of nitrogen oxides (NOx) emissions have led to increase of surface O3 in North China Plain (NCP) and Yangtze River Delta (YRD) by about 8 ppb. However, the severe O3 pollution in China can be mitigated because NOx controls led to the shift of O3 chemical regimes over NCP and YRD to transitional regime around 2019. In addition, the impacts of high fine particles (PM2.5) on O3 formation has declined because of the reduction of PM2.5 concentrations.
Key Points
Reductions of nitrogen oxides (NOx) led to increase of surface ozone (O3) in North China Plain and Yangtze River Delta
Shift of O3 chemical regimes with turning points between NOx‐ and volatile organic compound‐limited regimes around 2019
The impacts of high fine particles (PM2.5) on O3 formation has declined with reduction of PM2.5 concentrations
Dry conditions from a moderate El Niño during the fall of 2006 resulted in enhanced burning in Indonesia with fire emissions of CO approximately 4–6 times larger than the prior year. Here we use new ...tropospheric methane and CO data from the Aura Tropospheric Emission Spectrometer and new CO profile measurements from the Terra Measurements of Pollution in the Troposphere (MOPITT) satellite instruments with the Goddard Earth Observing System (GEOS)‐Chem model to estimate methane emissions of 4.25 ± 0.75 Tg for October–November 2006 from these fires. Errors in convective parameterization in GEOS‐Chem, evaluated by comparing MOPITT and GEOS‐Chem CO profiles, are the primary uncertainty of the emissions estimate. The El Niño related Indonesian fires increased the tropical distribution of atmospheric methane relative to 2005, indicating that tropical biomass burning can compensate for expected decreases in tropical wetland methane emissions from reduced rainfall during El Niño as found in previous studies.
Key Points
El Niño can increase methane emissions from tropical firesIndonesian fire emissions of methane estimated using satellite data
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