The effect of atmospheric sulfate reductions on diffuse radiation and photosynthesis in the United States during 1995–2013

Abstract

Aerosol optical depth (AOD) has been shown to influence the global carbon sink by increasing the fraction of diffuse light, which increases photosynthesis over a greater fraction of the vegetated canopy. Between 1995 and 2013, U.S. SO2 emissions declined by over 70%, coinciding with observed AOD reductions of 3.0 ± 0.6% yr−1 over the eastern U.S. In the Community Earth System Model (CESM), these trends cause diffuse light to decrease regionally by almost 0.6% yr−1, leading to declines in gross primary production (GPP) of 0.07% yr−1. Integrated over the analysis period and domain, this represents 0.5 Pg C of omitted GPP. A separate upscaling calculation that used published relationships between GPP and diffuse light agreed with the CESM model results within 20%. The agreement between simulated and data‐constrained upscaling results strongly suggests that anthropogenic sulfate trends have a small impact on carbon uptake in temperate forests due to scattered light.

Resource and physiological constraints on global crop production enhancements from atmospheric particulate matter and nitrogen deposition

“…For crop yield, the impact of nitrogen deposition we find is also consistent in sign with Liu et al (2013) over China. We underpredict the effect of nitrogen deposition on crops compared to the metric of sourced nitrogen content used by Ladha et al (2016). This may be due to our relatively short assumed nitrogen deposition time frame.…”

“…Lassaletta et al (2014) develop relationships between observed total nitrogen input and crop yield on a countrywide basis, but they do not disaggregate the impacts of deposition saying only that the input from deposition is small, but not negligible. While Ladha et al (2016) estimate that 6 % of nitrogen contained in global maize, wheat, and rice comes from deposited nitrogen, to date, there has been no global study of the change of yield associated with nitrogen deposition, with most studies concentrating on the impacts of nitrogen deposition on interactions with atmospheric CO 2 and carbon storage. Folberth et al (2016) neglect nitrogen deposition in their study of soil and meteorological data uncertainties in crop models due to the lack of available deposition data in a form suitable for global crop models.…”

“…However, the goal of this work is to explore only the direct impact of radiation changes (due to PM) on crop productivity, enabling a comparison with Schiferl and Heald (2018). For the nitrogen deposition simulations, NH x and NO y fluxes are applied daily as an additional source of fertilizer to the surface layer of the soil as NH + 4 and NO − 3 , respectively, due to their similar behaviors in soils (Ladha et al, 2016). We apply these deposition fluxes beginning 30 days prior to the planting date at each location.…”

The Atmospheric Imaging Mission for Northern Regions: AIM-North

“…Across North America, emissions of nitrogen oxides (NO x ), sulphur dioxide (SO 2 ), and most other air pollutants (with ammonia being the exception) have declined in recent decades as a result of emissions regulations on cars and power plants, including, e.g., the use of flue gas de-sulfurization (FGD), and an overall reduction in the use of coal (e.g., Kharol et al 2017). As a result, there is a decreasing trend in aerosol that can be detected from satellite observations of aerosol optical depth (AOD) over south-eastern Canada (e.g., Boys et al 2014;Keppel-Aleks and Washenfelder 2016). These changes in aerosols have led to significant health-related improvements for Canadians (2000-2011) (Stieb et al 2015).…”

An Evaluation of Semiempirical Models for Partitioning Photosynthetically Active Radiation Into Diffuse and Direct Beam Components

“…Different relative levels of these forms result in different irradiance patterns within plant canopies (Norman & Welles, ) and across heterogeneous terrain (Oliphant et al, , ) (see Table for a list of symbols). For example, global photosynthetically active radiation (PAR G )—a spectral subset of K G —is more efficient for canopy photosynthesis under conditions of diffuse beam PAR (PAR D ) than direct beam PAR (PAR S ) per unit PAR (Alton, ; Cheng et al, , ; Gu et al, , ; Keppel‐Aleks & Washenfelder, ; Mercado et al, ; Oliphant et al, ). Furthermore, the ratio of K D to K G has been found to lower the Bowen ratio (the ratio of sensible to latent heat flux) in a number of ecosystems (Steiner et al, ) and is important for the spatial distribution of net radiation in complex natural and urban terrain (e.g., Lindberg et al, ; Oliphant et al, ).…”