Tropospheric Ozone in the United Kingdom Chemistry and Aerosols (UKCA) model

Paul Griffiths

Cambridge University and NCAS Climate

Visiting Scientist, NARIT, Thailand

Talk outline

‣ Ozone in the troposphere‣ Is formed from Volatile Organic Compounds (VOC) and nitrogen oxide

emissions‣ Is a non-linear system‣ Large levels of NOx cause a decrease in ozone production

‣ The UKCA model and what it says about ozone in the present day ‣ Where are regions of ozone production and destruction?‣ How accurate are UKCA predictions of ozone?

‣ Using UKCA to examine how ozone may change in future ‣ Anthropogenic emissions of NOx and VOC change‣ Land is used differently - deforestation changes biogenic (natural)

emissions

UK Chemistry and Aerosols project (UKCA)

Model components of Earth System

‣ UK Met Office Unified Model (UM) is a weather forecast model run in climate mode - basis for HadGEM/HadES models, next generation UK-ESM1

‣ Online chemistry - feedbacks between atmospheric composition, radiation and transport

Model components of Earth System

‣ UK Met Office Unified Model (UM) is a weather forecast model run in climate mode - basis for HadGEM/HadES models, next generation UK-ESM1

‣ Online chemistry - feedbacks between atmospheric composition, radiation and transport

Ozone in the troposphere

Ozone in the troposphere

‣ To a chemist, the atmosphere is an oxidizing environment

‣ Pollution released into the atmosphere is slowly degraded by oxidation

‣ Viewed a certain way, the atmosphere is a low temperature combustion system.

‣ Volatile organic compounds are transformed into CO2

‣ VOC + O2 → CO2 + H2O‣ Ozone is can be produced or destroyed

during this process ‣ Ozone affects other pollutants, e.g. NO2

‣ Ozone ‣ A key component of UK Air Quality‣ Implications for health

Ozone from a chemist’s perspective - about in situ production/loss

‣ Local or regional emissions of volatile organic compounds (VOC) ‣ VOC can have industrial or natural sources.‣ React with oxidant OH to make peroxy radicals, RO2‣ Peroxy radicals, RO2 react with local or regional emissions of NO to make NO2‣ NO2 is photolysed rapidly to make ozone ‣ More ozone is produced than is consumed = ozone production ‣ Ozone production requires sunlight, VOC and NO

O3 + h⌫(� < 310nm) ! O2 +O1D

O1D+H2O ! 2OH

OH+VOC ! RO2 +H2O

RO2 +NO ! NO2 +RO

NO2 + h⌫ +O2 !! O3 +NO

Ozone from a chemist’s perspective - about in situ production/loss

Primary pollutants, local emissions

‣ Local or regional emissions of volatile organic compounds (VOC) ‣ VOC can have industrial or natural sources.‣ React with oxidant OH to make peroxy radicals, RO2‣ Peroxy radicals, RO2 react with local or regional emissions of NO to make NO2‣ NO2 is photolysed rapidly to make ozone ‣ More ozone is produced than is consumed = ozone production ‣ Ozone production requires sunlight, VOC and NO

O3 + h⌫(� < 310nm) ! O2 +O1D

O1D+H2O ! 2OH

OH+VOC ! RO2 +H2O

RO2 +NO ! NO2 +RO

NO2 + h⌫ +O2 !! O3 +NO

Ozone from a chemist’s perspective - cycle of O3 production

Ozone is regenerated and amplified

‣ Ozone initiates and is the product of this chemistry.

‣ When NO and VOC present in sufficient concentration, more ozone is produced than is consumed = ozone production

‣ Ozone production requires sunlight, VOC and NO

‣ OH product affects lifetime of CH4

O3 + h⌫(� < 310nm) ! O2 +O1D

O1D+H2O ! 2OH

OH+VOC ! RO2 +H2O

RO2 +NO ! NO2 +RO

NO2 + h⌫ +O2 !! O3 +NO

Ozone from a chemist’s perspective - cycle of O3 production

‣ Ozone initiates and is the product of this chemistry.

‣ When NO and VOC present in sufficient concentration, more ozone is produced than is consumed = ozone production

‣ Ozone production requires sunlight, VOC and NO

‣ OH product affects lifetime of CH4

O3 + h⌫(� < 310nm) ! O2 +O1D

O1D+H2O ! 2OH

OH+VOC ! RO2 +H2O

RO2 +NO ! NO2 +RO

NO2 + h⌫ +O2 !! O3 +NO

Ozone from a chemist’s perspective - cycle of O3 production

‣ Ozone initiates and is the product of this chemistry.

‣ When NO and VOC present in sufficient concentration, more ozone is produced than is consumed = ozone production

‣ Ozone production requires sunlight, VOC and NO

‣ OH product affects lifetime of CH4

O3 + h⌫(� < 310nm) ! O2 +O1D

O1D+H2O ! 2OH

OH+VOC ! RO2 +H2O

RO2 +NO ! NO2 +RO

NO2 + h⌫ +O2 !! O3 +NO

More info on Friday at 0930 !!

Ozone in the troposphere

Ozone production in UKCA: ozone production/loss

‣ Ozone is produced close to the surface via VOC oxidation‣ Some ozone is lost via deposition to the surface (dry deposition)‣ Regions with high NOx may not produce as much ozone

Ozone production at surface Ozone loss at surface

Ozone production in and near to tropics

‣ There is significant loss in the mid troposphere (via HO2 + O3)‣ Most global tropospheric ozone is produced in the NH and lost in the tropics

Ozone production in UKCA: ozone production/loss

Ozone production at surface

UKCA vs Simone Tilmes' ozonesonde data comparison

UKCA vs Simone Tilmes' ozonesonde data comparison

UKCA vs Simone Tilmes' ozonesonde data comparison

Ozone in future climate:

Vegetation, emissions and chemistry at work

How does atmospheric chemistry change in future climate?

‣ Ozone levels in future climate is a wicked problem [‘too important to ignore, too difficult to solve’]

‣ Anthropogenic emissions of VOC and NOx will change

‣ The amount of water vapour increases so OH increases

‣ What happens to the atmospheric dynamics and transport of ozone?

‣ Biomass burning / lightning (future study)

‣ The temperature increases - most reactions go faster, plant emissions increase e.g. isoprene, C5H8 (emitted by trees)

‣ Land use / land cover is changing

Isoprene emissions in future climate

‣ 500 Tg C isoprene emitted annually

‣ Broad-leafed trees major emitters, crops emit less

‣ Reacts quickly in the atmosphere in the presence of NOx to produce ozone.

‣ As temperature increases, isoprene emission is enhanced

‣ As CO2 increases, isoprene emission is inhibited

Need to consider temperature, CO2 and land use to quantify isoprene

Land use changes - from Sheffield Digital Vegetation Model

Change in grid cell fraction in the model in year 2095

Isoprene emissions changes - from MEGAN

Change in isoprene emissions in the model year 2095

How does ozone respond in future climate?

Squire et al., 2015, Atm Chem Phys

1018 O. J. Squire et al.: Influence of future cropland expansion on tropospheric ozone

Discussion

Pa

per

|D

iscussion

Pa

per

|D

iscussion

Pa

per

|D

iscussion

Pa

per

|

Latitude

Longitude−180° −90° 0° 90° 90°

−60°

−30°

0°

35°

70°

●Sam

●Hil

●SaC●Her

●Nat

●Asc●Cot

●Mal●Ire

●Reu

●KuL●Jav

BASE

10 20 30 40 50 60 70

Fig. 4. Modelled five year mean near surface (<720 m) O3 (ppb) for the year 2000 (BASE).Locations of measurement sites used in Figure 3 are shown. Sam = Samoa, Hil = Hilo, SaC =San Christobal, Her = Heredia, Nat = Natal, Asc = Ascension, Cot = Cotonou, Ire = Irene, Mal= Malindi, Reu = Reunion, KuL = Kuala Lumpar, Jav = Java.

33

Fig. 4. Modelled five year mean near surface (< 720 m) O3 (ppb) for the year 2000(BASE). Locations of measurement sites used in Fig. 3 are shown. Sam=Samoa, Hil=Hilo,SaC=San Christobal, Her=Heredia, Nat=Natal, Asc=Ascension, Cot=Cotonou, Ire= Irene,Mal=Malindi, Reu=Reunion, KuL=Kuala Lumpar, Jav= Java.

37

Fig. 4. Modelled five-year mean near-surface (< 720m) O3 (ppb)for the year 2000 (BASE). Locations of measurement sites usedin Fig. 3 are shown. Sam=Samoa, Hil =Hilo, SaC=San Chris-tobal, Her =Heredia, Nat =Natal, Asc =Ascension, Cot =Cotonou,Ire = Irene, Mal =Malindi, Reu =Reunion, KuL=Kuala Lumpur,Jav = Java.

Discu

ssio

nP

ap

er

|D

iscussio

nP

ap

er

|D

iscu

ssio

nP

ap

er

|D

iscu

ssio

nP

ap

er

|

Latit

ude

Longitude

−80°

−40°

0°

40°

80°(a) ∆ Climate

−180° −90° 0° 90° 180°

(b) ∆ Isoprene emissions w/ climate

(c) ∆ Anthropogenic emissions

−80°

−40°

0°

40°

80°(d) ∆ Land use

−80°

−40°

0°

40°

80°

−180° −90° 0° 90° 180°

(e) ∆ CO2 Inhibition (f) ∆ All factors

<−10 −8 −6 −4 −2 0 2 4 6 8 >10

Fig. 5. Changes in five year mean near surface (< 720 m) O3 (2095 – 2000) caused by di�erentenvironmental variables. Changes are considered significant (stippled) if they are greater than2 times the standard deviation for the five year mean (i.e. approximately the 5 % level).

38

Fig. 5. Changes in five-year mean near-surface (< 720m) O3(2095–2000) caused by different environmental variables. Changesare considered significant (stippled) if they are greater than 2 timesthe standard deviation for the five-year mean (i.e. approximately the5% level).

(“influx”) and sink to the surface by dry deposition. Here wedefine Ox as the sum of O3, atomic oxygen and reactive ni-trogen species (NOy).Figure 5a shows the effect of climate change on O3. The

increased SSTs in the climate change integration cause a gen-eral warming of the boundary layer by 1–3 �C. As both O3production and destruction usually have a positive temper-

ature dependence, the expected effect would be an increasein O3 in regions where O3 production dominates (continen-tal regions near a NOx source), and a decrease in O3 wherethere is net O3 destruction (the remote ocean and low-NOxhigh-VOC environments such as the rainforest). This is re-flected in both the higher production (+393 Tgyr�1 (+6%))and loss (+546 Tgyr�1 (+10%)) terms in the Ox budget forclimate change (Table 2). The effect of higher temperatureson Ox loss is greater than on Ox production, leading to anoverall decrease in the net chemical tendency. The responseof the atmospheric system is to increase the O3 burden by7 Tg (2%), mainly due to increased influx from the strato-sphere.Warming is significantly higher than 1–3 �C over some re-

gions, notably Brazil and high northern latitudes (6–8 �C).The particularly strong warming over Brazil causes watervapour to decrease, following a drying of the surface. Eventhough this rainforest-covered region is an area where O3destruction dominates, the reduction in water vapour dimin-ishes the potential for O3 loss through the O1D+H2O reac-tion, leading to O3 increases. Over the oceans the oppositeeffect occurs, with higher temperatures leading to increasedatmospheric water vapour and increased O3 loss throughO1D+H2O.Another factor influencing O3 over the oceans is the

change in long-range transport of peroxyacetyl nitrate(PAN). PAN is produced over land where NOx and VOCs in-teract. As shown in Fig. 6a major source regions are the con-tinental tropics, southeast USA, Europe and Southeast Asia.Transport of PAN, and subsequent thermal decomposition,provides a source of NOx (leading possibly to O3 production)over the remote oceans. PAN decomposition is very stronglytemperature dependent; in a warmer climate PAN transport tothe remote ocean is reduced. The largest reductions in PANare calculated over South America (Fig. 6b) where PAN pro-duction is high in the BASE run, and the increase in temper-ature under climate change is the largest. This contributes todecreases in O3 of up to 8 ppb (⇠ 23%) in the surroundingoceans.The largest changes in isoprene emissions due to climate

change (Fig. 2c) occurred in the tropics and may be sum-marised as generally elevated emissions except in the north-east Amazon and parts of the Maritime Continent. Isopreneemissions are also heightened to a smaller degree over south-east USA. The effect of these isoprene emission changeson O3 is shown in Fig. 5b. The tropical lower troposphereis NOx-limited and VOC-rich. Accordingly, where isopreneemissions increase in the tropics, decreases in O3 are cal-culated. This is due to increased ozonolysis of isoprene byO3 and greater sequestration of NOx as isoprene nitrates.Where isoprene decreases in the tropics the opposite effectsoccur, and O3 increases. In contrast, the increases in iso-prene emissions in the VOC-limited eastern USA cause O3to increase by 2–4 ppb (⇠ 5%). Similar, regionally heteroge-neous O3 responses to isoprene emissions were calculated in

Atmos. Chem. Phys., 14, 1011–1024, 2014 www.atmos-chem-phys.net/14/1011/2014/

‣ How does ozone respond?‣ Single perturbations to

climate system for each forcer

‣ Focus on isoprene (VOC) from vegetation.

‣ Then allow perturbations to interact

‣ UM/UKCA N48L60, CheT chemistry,‣ isoprene emissions from

MEGAN‣ vegetation distribution

from Sheffield Dynamic Vegeation model,

‣ other emissions according to IPCC REF B2 scenario

How does ozone respond in future climate?

Squire et al., 2015, Atm Chem Phys

How does ozone respond in future climate?

Squire et al., 2015, Atm Chem Phys

How does ozone respond in future climate?

Squire et al., 2015, Atm Chem Phys

How does ozone respond in future climate?

Dots indicate regions of significant change compared to model variability

Conclusions

Conclusions

‣ Ozone in global climate models is challenging‣ While Emissions, chemistry have strong effect, land use change play a

significant role.‣ Strong effects where vegetation cover is changing due to changes to deposition.

‣ Underpinning emissions estimates and sinks depend crucially on land use and land cover estimates

‣ Air quality, health, climate connect at local level‣ Long range transport of ozone precursors also important regionally

‣ Tropospheric ozone burden important to methane lifetime and radiative forcing

Thank you!

Questions?