Air Pollution threats to crops and semi-natural vegetation ... · Air Pollution threats to crops...

David Fowler,

et al

Air Pollution threats to crops and semi-natural vegetation

in the 21st century

CAPER April 2014

QUESTIONS

• Will the global total and scale of effects increase or decline?

• Will there be continued improvements in the old developed economies as the rapidly developing regions become more polluted

• Will climate change erode benefits of control measures ?

• Will ecological impacts become a more important driver of policy?

OUTLINE

• Projected emissions 2010-2100 • Effects of changes in climate on emissions, • Other important changes (land use, transport,

energy sources, global distribution of major industry)

• Uncertainties (known unknowns) • Projected deposition and exposure of crops

and semi-natural vegetation • Ecosystems v human health

NOX EMISSIONS (VAN VUUREN et al 2011)

N2O EMISSIONS 1950-2100 (VAN VUUREN et al 2011)

AMMONIA EMISSIONS VAN VUUREN et al 2011

Global sulphur emissions

Global Sulphur emissions in 2100 50 Tg-S (40 -100)

Overall emission trends

• A decline in NOx emissions , but not sufficient to substantially reduce zonal O3 background

• An increase in NH3 emissions seems likely • A decline in Sulphur emissions possibly to 50

Tg-S annually • VOC, a decline in vehicle and industrial

emissions and uncertainty in BVOC due to changes in land use

Effects of changes in climate (and land use)

Climate interactions with emissions

• The biological processes are very sensitive to temperature and water availability in soils

• Most of the chemical processes are temperature sensitive

• The phase partitioning, which strongly influences surface –atmosphere exchange is very sensitive to temperature and the energy balance at the surface.

• So where should we look for the interactions?

Biological responses,

Microbiological, plant At the surface –atmosphere interface

Atmosphere

Climate - Nitrogen cycle interactions

Rate coefficients oxidants

Effect of temperature on NH3 emission from vegetation

KhsKha KhhonoKhc

Kn1 Ks1Kc1Ka

NH3,aq CO2,aq HNO2,aq

NH3 CO2 HNO2 SO2

SO2,aq

CO32- SO3

2- SO42-

NH4+ HCO3

- NO2- HSO3

- HSO4-

Ks2Kc2 Ks3

Kw

H2O H++OH-

χd

Rd

AQUEOUS

GASEOUS

Kha

χs(NH3)

Rs

Rcut

Fcut

Rb

Ra{z-d}

χ{z-d}

χ{z0’}=χc

χ{z0}

WET DRY

HNO3

HCl

Cl-

NO3- H2O2

O3

APOPLAST

Ft

Fd

FsK+Mg2+

Na+ Ca2

+

K+Mg2+

Na+ Ca2

+

Ka NH3,aqNH4+

Kw

H2O H++OH-

NH3 NH4+

P NH3=104.1-4507/T(NH4+/H+)

Temperature response of NH3 emission

Flechard and Fowler, QJRMS, 1998

• Relatively small changes in surface temperature yield substantial changes in ammonia emission

• Towards a climate-dependent paradigm of ammonia emission and deposition Mark A. Sutton et al Phil Trans RS 2013

Climate dependent ammonia emission

Global emissions 2010 65 Tg NH3-N......possibly 132 Tg NH3-N by 2100 Sutton et al 2013

O

14 papers History of N cycle Jim Galloway Biological N fixation Peter Vitousek Soil emissions of NO Kim Pilegaard Soil emissions of N2O Klaus Butterbach-Bahl Global Emissions of N2 and N2O Lex Bouwman Global NH3 emissions Mark Sutton Organic nitrogen in the atmos Tim Jickells N deposition in the USA Robin Dennis Watershed N budgets Gilles Billen The marine N cycle Maren Voss Ice sheet N Eric Wolff Terrestrial N-C cycle interactions Sonke Zaehle Effects of human modification of the N cycle Jan Willem Erisman

OBSERVATIONS

• There are no mechanistic global N models integrating atmos, terrest and marine systems

• The three Nr communities (atmos, terrestrial, marine) operate independently.

• Some aspects of the global N cycle are simulated in mechanistic detail (CTM, with NOy, ozone, some with NHx) coupled to climate models

• Terrestrial N cycling at site, catchment and regional scale is in progress…(also marine)

PROCESSING REACTIVE NITROGEN

Aerosol deposition to terrestrial surfaces and climate

MECHANISM LEADING TO FAST NITRATE & AMMONIUM DEPOSITION NH4NO3(S, AQ) NH3(G) + HNO3(G); KE = FN(T, RH)

Temperature gradient

Gradient in equilibrium dissociation constant Ke [NH3]x[HNO3]

[HNO3] [NH3]

Driver for evaporation

Gradient in actual [NH3]x[HNO3]

NH4NO3

HNO3 NH3

REGIONAL EFFECTS OF CHANGES IN CLIMATE ON REACTIVE NITROGEN

Simpson et al 2014 EMEP-Europe

Deposition and exposure of ecosystems

Ozone

OH HO 2

RO 2 RO

R - H O RH

H 2 O 2

HCHO

HNO 3

ROOH

NO 2

H 2 O

HO 2

O 2

O 3 NO 2

NO

sunlight

HO 2

NO 2

NO

O 2

O 3 sunlight sunlight

sunlight

O 2

POLLUTED ATMOSPHERE

NO2 > 20 ppt

VOCs

SEASONAL VARIATION OF SURFACE OZONE

Ensemble mean of 26 ACCENT Photocomp models Stevenson et al 2006

Deposition and exposure of ecosystems

• Global models reproduce the broad regional, zonal and seasonal variability in tropospheric ozone

• But for many monitoring stations at the surface they do not reproduce observed long term trends

• Scale, emissions, land use and very large sub-grid variability all contribute

Mean of 3 models

Projected changes in surface O3 (2050-2000) during the peak O3 season due to climate change(HadGEM SRES A1B)

Deposition and exposure of ecosystems

• In the three CCMs, annual-mean surface O3 generally decreases due to climate change but increases in parts of the more polluted regions, consistent with previous studies.

• Surface O3 increases in high NOx regions are up to 6 ppbv in the annual average and up to 14 ppbv in the season of present-day maximum surface O3.

Global effects of ozone deposition

• The ozone exposure in most crop growing regions of the N. Hemisphere is sufficient to reduce productivity

• Semi-natural vegetation shows a similar range of sensitivity to that of crops

• Anticipated changes in emissions are unlikely to eliminate the effects

Deposition and exposure of ecosystems

• total annual losses worth $12 billion to $21 billion

• Avnery et al 2011

QUESTIONS AND SOME ANSWERS • Will the global total and scale of effects increase or

decline?...probably increase • Will there be continued improvements in the old

developed economies as the rapidly developing regions become more polluted.... Yes, but the scope of further measures is small

• Will climate change erode benefits of control measures ?....probably yes

• Will ecological impacts become a more important driver of policy?...in the short term this seems unlikely given the effects of air quality on human health

Recent OECD report

The “Baseline” scenario projects that, unless the global energy mix changes, fossil fuels will

supply about 85% of energy demand in 2050, implying a 50% increase in greenhouse gas (GHG)

emissions and worsening urban air pollution. The impact on the quality of life of our citizens would be disastrous.

The number of premature deaths from exposure to particulate pollutants could double

from current levels to 3.6 million every year. Global water demand is projected to increase by 55% by 2050 Competition for water would intensify, resulting in up to 2.3 billion more people

living in severely water-stressed river basins. By 2050, global terrestrial biodiversity is projected to decline by a further 10%. Crop loss from ozone (air pollution) is likely to be at least similar to current levels

We are on track for 4 deg C warming

There are things we could do....

Benefits

Global benefits of 16 selected CH4 – O3 – BC control measures

UN

EP, 2

011

Benefits of control measures at country scale

•Worldwide implementation of 16 measures will have a relatively rapid impact on global mean temperature (GMT) : 0.5° C (80% of expected GMT within 20 yrs!).

•Reduction of 0.7 to 4.7 million premature deaths avoided (mainly in S and E Asia • 30 to 135 million metric tonnes yield increase in cereal crops

•Ozone reduction measures, especially through CH4, are an absolute no- regret policy for air pollution and climate. CH4 – O3 benefits in crop yields occur at hemispheric scale. •We still have to greatly reduce CO2 emissions, but the measures presented by this assessment provide an excellent opportunity to contribute to reducing climate change, and offer important benefits for human health and crop production

Conclusions