Simulation of the Ecosystem Productivity Responses to Aerosol Diffuse Radiation Fertilization Effects over the Pan-Arctic during 2001–19

The pan-Arctic is confronted with air pollution transported from lower latitudes.Observations have shown that aerosols help increase plant photosynthesis through the diffuse radiation fertilization effects(DRFEs).While such DRFEs have been explored at low to middle latitudes,the aerosol impacts on pan-Arctic ecosystems and the contributions by anthropogenic and natural emission sources remain less quantified.Here,we perform regional simulations at 0.2o×0.2ousing a well-validated vegetation model(Yale Interactive terrestrial Biosphere,YIBs)in combination with multi-source of observations to quantify the impacts of aerosol DRFEs on the net primary productivity(NPP)in the pan-Arctic during 2001-19.Results show that aerosol DRFEs increase pan-Arctic NPP by 2.19 Pg C(12.8%)yr^(-1)under clear-sky conditions,in which natural and anthropogenic sources contribute to 8.9% and 3.9%,respectively.Under all-sky conditions,such DRFEs are largely dampened by cloud to only 0.26 Pg C(1.24%)yr^(-1),with contributions of 0.65% by natural and 0.59% by anthropogenic species.Natural aerosols cause a positive NPP trend of 0.022% yr^(-1)following the increased fire activities in the pan-Arctic.In contrast,anthropogenic aerosols induce a negative trend of-0.01% yr^(-1)due to reduced emissions from the middle latitudes.Such trends in aerosol DRFEs show a turning point in the year of 2007 with more positive NPP trends by natural aerosols but negative NPP trends by anthropogenic aerosols thereafter.Though affected by modeling uncertainties,this study suggests a likely increasing impact of aerosols on terrestrial ecosystems in the pan-Arctic under global warming.

Comparison of Ozone and PM2.5 Concentrations over Urban,Suburban,and Background Sites in China

Surface ozone(O3)and fine particulate matter(PM2.5)are dominant air pollutants in China.Concentrations of these pollutants can show significant differences between urban and nonurban areas.However,such contrast has never been explored on the country level.This study investigates the spatiotemporal characteristics of urban-to-suburban and urban-tobackground difference for O3(Δ[O3])and PM2.5(Δ[PM2.5])concentrations in China using monitoring data from 1171 urban,110 suburban,and 15 background sites built by the China National Environmental Monitoring Center(CNEMC).On the annual mean basis,the urban-to-suburbanΔ[O3]is−3.7 ppbv in Beijing-Tianjin-Hebei,1.0 ppbv in the Yangtze River Delta,−3.5 ppbv in the Pearl River Delta,and−3.8 ppbv in the Sichuan Basin.On the contrary,the urban-to-suburbanΔ[PM2.5]is 15.8,−0.3,3.5 and 2.4μg m^−3 in those areas,respectively.The urban-to-suburban contrast is more significant in winter for bothΔ[O3]andΔ[PM2.5].In eastern China,urban-to-background differences are also moderate during summer,with−5.1 to 6.8 ppbv forΔ[O3]and−0.1 to 22.5μg m^−3 forΔ[PM2.5].However,such contrasts are much larger in winter,with−22.2 to 5.5 ppbv forΔ[O3]and 3.1 to 82.3μg m^−3 forΔ[PM2.5].Since the urban region accounts for only 2%of the whole country’s area,the urban-dominant air quality data from the CNEMC network may overestimate winter[PM2.5]but underestimate winter[O3]over the vast domain of China.The study suggests that the CNEMC monitoring data should be used with caution for evaluating chemical models and assessing ecosystem health,which require more data outside urban areas.

A New Parameterization of Canopy Radiative Transfer for Land Surface Radiation Models

A new parameterization of canopy asymmetry factor on phase function,which is dependent on the leaf normal distribution and leaf reflection/transmission,is derived. This new parameterization is much more accurate than the existing scheme. In addition,the new solutions for both the diffuse and direct radiation can be obtained using the Eddington approximation. It is found that the direct radiation can be described as a function of the diffuse radiation. This new approach offers a substantial improvement in accuracy,as compared with the hemispheric constant method,for both isotropic and anisotropic cases. Given the analytical nature of the solution and its high accuracy,we recommend the new parameterization for application in land surface radiation modeling.

Large potential of strengthening the land carbon sink in China through anthropogenic interventions

The terrestrial ecosystem in China mitigates 21%-45%of the national contemporary fossil fuel CO_(2) emissions every year.Maintaining and strengthening the land carbon sink is essential for reaching China’s target of carbon neutrality.However,this sink is subject to large uncertainties due to the joint impacts of climate change,air pollution,and human activities.Here,we explore the potential of strengthening land carbon sink in China through anthropogenic interventions,including forestation,ozone reduction,and litter removal,taking advantage of a well-validated dynamic vegetation model and meteorological forcings from 16 climate models.Without anthropogenic interventions,considering Shared Socioeconomic Pathways(SSP)scenarios,the land sink is projected to be 0.26-0.56 Pg C a^(-1) at 2060,to which climate change contributes 0.06-0.13 Pg C a^(-1) and CO_(2) fertilization contributes 0.08-0.44 Pg C a^(-1) with the stronger effects for higher emission scenarios.With anthropogenic interventions,under a close-to-neutral emission scenario(SSP1-2.6),the land sink becomes 0.47-0.57 Pg C a^(-1) at 2060,including the contributions of 0.12 Pg C a^(-1) by conservative forestation,0.07 Pg C a^(-1) by ozone pollution control,and 0.06-0.16 Pg C a^(-1) by 20%litter removal over planted forest.This sink can mitigate 90%-110% of the residue anthropogenic carbon emissions in 2060,providing a solid foundation for the carbon neutrality in China.