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Earth's Systems / Energy flow / Greenhouse trapping and release to space / Tropospheric ozone, NOx-VOC chemistry and aerosol nucleation

Tropospheric ozone, NOx-VOC chemistry and aerosol nucleation

How nitrogen oxides, volatile organic compounds and sunlight make ozone in the lower atmosphere, which regime limits that production, and how sulfuric acid, ammonia and organic vapours nucleate new aerosol particles that grow into cloud seeds.

Boundary: where this process starts

Starts with: Precursors enter the troposphere: lightning makes about 5 Tg N/yr of NOx, plants emit about 1,000 Tg/yr of volatile organic compounds (half isoprene), and fuel

Boundary: where it ends

Ends after: Tropospheric ozone warms the climate (CO and NMVOC emissions alone give about 0.44 W/m2 of forcing) and damages crops and lungs; Low-volatility oxidation products of biogenic VOCs grow the clusters to cloud-seed size: nucleation supplies about 54% of cloud condensation nuclei today and 67

PARTICIPANTSRESOURCESAtmosphereNitrogen oxidesAerosolsVegetationHydroxylradicalsOzoneVolatileorganiccompoundsNitrogen oxidesAerosolsInfraredradiationImpact +4 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.80%Impact -2 of 5. Click for details and evidence.20%Impact +3 of 5. Click for details and evidence.Impact +2 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.↻ balances · strong · 0.6Impact +4 of 5. Click for details and evidence.Impact +2 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Precursors enter the troposphere: lightning makes about 5 Tg N/yr of NOx, plants emit about 1,000 Tg/yr of volatile organic compounds (half isoprene), and fuel : makes Volatile organic compoundsmakesPrecursors enter the troposphere: lightning makes about 5 Tg N/yr of NOx, plants emit about 1,000 Tg/yr of volatile organic compounds (half isoprene), and fuel : makes Nitrogen oxidesmakesSunlight splits NO2 to make ozone; OH-driven oxidation of VOCs and CO makes peroxy radicals that turn NO back to NO2 without consuming ozone, so ozone accumulat: makes OzonemakesSunlight splits NO2 to make ozone; OH-driven oxidation of VOCs and CO makes peroxy radicals that turn NO back to NO2 without consuming ozone, so ozone accumulat: uses up Volatile organic compoundsuses upSunlight splits NO2 to make ozone; OH-driven oxidation of VOCs and CO makes peroxy radicals that turn NO back to NO2 without consuming ozone, so ozone accumulat: uses Nitrogen oxidesWhich ingredient limits ozone production?: makes OzonemakesNOx-limited (most of the remote and rural troposphere): more NOx means more ozone (about 80%, estimate): uses OzoneNOx-limited (most of the remote and rural troposphere): more NOx means more ozone (about 80%, estimate): uses Nitrogen oxidesVOC-limited (polluted urban cores): extra NOx consumes radicals and lowers local ozone (about 20%, estimate): uses up Ozoneuses upVOC-limited (polluted urban cores): extra NOx consumes radicals and lowers local ozone (about 20%, estimate): uses Volatile organic compoundsOzone is lost by photochemistry and by deposition to the surface, and some enters from the stratosphere; warming and more methane raise the stratospheric influx: uses up Ozoneuses upTropospheric ozone warms the climate (CO and NMVOC emissions alone give about 0.44 W/m2 of forcing) and damages crops and lungs: uses OzoneTropospheric ozone warms the climate (CO and NMVOC emissions alone give about 0.44 W/m2 of forcing) and damages crops and lungs: uses Infrared radiationSulfuric acid from SO2 oxidation nucleates new particles: 100 ppt of ammonia raises the nucleation rate 100 to 1,000-fold and ions add a factor of 2 to 10: makes AerosolsmakesLow-volatility oxidation products of biogenic VOCs grow the clusters to cloud-seed size: nucleation supplies about 54% of cloud condensation nuclei today and 67: uses Volatile organic compoundsLow-volatility oxidation products of biogenic VOCs grow the clusters to cloud-seed size: nucleation supplies about 54% of cloud condensation nuclei today and 67: uses AerosolsmakesVolatile organic compounds: makesmakesNitrogen oxides: makesmakesOzone: makesuses upVolatile organic compounds: uses upusesNitrogen oxides: usesmakesOzone: makesusesOzone: usesusesNitrogen oxides: usesuses upOzone: uses upusesVolatile organic compounds: usesuses upOzone: uses upusesOzone: usesusesInfrared radiation: usesmakesAerosols: makesusesVolatile organic compounds: usesusesAerosols: usesStart: Troposphericozone, NOx-VOCchemistry and aeros…STARTStart: Tropospheric ozone, NOx-VOC chemistry and aerosol nucleationEnd: Troposphericozone, NOx-VOCchemistry and aeros…ENDEnd: Tropospheric ozone, NOx-VOC chemistry and aerosol nucleationPrecursors enter thetroposphere: lightningmakes about 5 Tg N/…📄3Precursors enter the troposphere: lightning makes about 5 Tg N/yr of NOx, plants emit about 1,000 Tg/yr of volatile organic compounds (half isoprene), and fuel Sunlight splits NO2 tomake ozone; OH-drivenoxidation of VOCs a…📄3Sunlight splits NO2 to make ozone; OH-driven oxidation of VOCs and CO makes peroxy radicals that turn NO back to NO2 without consuming ozone, so ozone accumulatWhich ingredient limitsozone production?📄1Which ingredient limits ozone production?NOx-limited (most ofthe remote and ruraltroposphere): more N…📄2NOx-limited (most of the remote and rural troposphere): more NOx means more ozone (about 80%, estimate)VOC-limited (pollutedurban cores): extra NOxconsumes radicals a…📄1VOC-limited (polluted urban cores): extra NOx consumes radicals and lowers local ozone (about 20%, estimate)Ozone is lost byphotochemistry and bydeposition to t…📄3Ozone is lost by photochemistry and by deposition to the surface, and some enters from the stratosphere; warming and more methane raise the stratospheric influxTropospheric ozonewarms the climate (COand NMVOC emissio…📄2 ↗1Tropospheric ozone warms the climate (CO and NMVOC emissions alone give about 0.44 W/m2 of forcing) and damages crops and lungsSulfuric acid from SO2oxidation nucleates newparticles: 100 ppt …📄1Sulfuric acid from SO2 oxidation nucleates new particles: 100 ppt of ammonia raises the nucleation rate 100 to 1,000-fold and ions add a factor of 2 to 10Low-volatilityoxidation products ofbiogenic VOCs grow t…📄1 ↗2Low-volatility oxidation products of biogenic VOCs grow the clusters to cloud-seed size: nucleation supplies about 54% of cloud condensation nuclei today and 67
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
What am I looking at? The concepts on every map
Participant
Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
Resource
Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
Step
One thing that happens in a process. Every step has at least one participant and carries evidence.
Decision fork
A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
Loop
A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
Size of impact
Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
Evidence
The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
Boundary
Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
Subprocess
A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
Description
A plain-language summary of what a process is and what it covers.
Hypothesis
A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.

Every step, with its evidence

The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.

Precursors enter the troposphere: lightning makes about 5 Tg N/yr of NOx, plants emit about 1,000 Tg/yr of volatile organic compounds (half isoprene), and fuel
LightningVegetationHuman activitiesNitrogen oxidesVolatile organic compounds
Evidence (3) · added by Briangold-Claude
  • Schumann & Huntrieser 2007, The global lightning-induced nitrogen oxides source, Atmos. Chem. Phys. 7:3823-3907, https://acp.copernicus.org/articles/7/3823/2007/: The best estimate of the global lightning NOx source is 5 +/- 3 Tg N per year. (confidence 0.9)
  • Guenther et al. 2012, The Model of Emissions of Gases and Aerosols from Nature version 2.1 (MEGAN2.1), Geosci. Model Dev. 5:1471-1492, https://gmd.copernicus.org/articles/5/1471/2012/: Isoprene comprises about half of the total global biogenic VOC emission of 1 Pg (1000 Tg) per year; tropical trees on 18% of land supply about 80% of terpenoid emissions. (confidence 0.9)
  • IPCC AR6 WG1 2021, Chapter 6: Short-lived Climate Forcers, https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-6/: Emissions of NOx, CO and NMVOCs enhance tropospheric ozone production. (confidence 0.85)
Sunlight splits NO2 to make ozone; OH-driven oxidation of VOCs and CO makes peroxy radicals that turn NO back to NO2 without consuming ozone, so ozone accumulat
AtmosphereHydroxyl radicalsNitrogen oxidesOzoneVolatile organic compoundsNitrogen oxides
Evidence (3) · added by Briangold-Claude
  • Young et al. 2013, Pre-industrial to end 21st century projections of tropospheric ozone from ACCMIP, Atmos. Chem. Phys. 13:2063-2090, https://acp.copernicus.org/articles/13/2063/2013/: The present-day ensemble mean tropospheric ozone burden is 337 +/- 23 Tg, about 30% higher than the 1850 time slice. (confidence 0.9)
  • Monks et al. 2015, Tropospheric ozone and its precursors from the urban to the global scale from air quality to short-lived climate forcer, Atmos. Chem. Phys. 15:8889-8973, https://acp.copernicus.org/articles/15/8889/2015/: Ozone is produced by the oxidation chemistry it largely initiates, centred on OH, NOx and VOC reactions. (confidence 0.85)
  • NOAA CSL, Scientific Assessment of Ozone Depletion 2022: Twenty Questions, https://csl.noaa.gov/assessments/ozone/2022/twentyquestions/: In the troposphere ozone is formed by a different set of reactions involving naturally occurring gases and pollution gases. (confidence 0.8)
⑂ Which ingredient limits ozone production?
AtmosphereNitrogen oxidesOzone
Evidence (1) · added by Briangold-Claude
  • Sillman 1999, The relation between ozone, NOx and hydrocarbons in urban and polluted rural environments, Atmos. Environ. 33:1821-1845, https://doi.org/10.1016/S1352-2310(98)00345-8: Ozone production is NOx-sensitive or VOC-sensitive depending on the ratio of hydrocarbons to NOx in urban and polluted rural air; the 80/20 split by volume of the troposphere is an estimate. (confidence 0.6)
NOx-limited (most of the remote and rural troposphere): more NOx means more ozone (about 80%, estimate)
AtmosphereNitrogen oxidesOzoneNitrogen oxides
Evidence (2) · added by Briangold-Claude
  • Sillman 1999, The relation between ozone, NOx and hydrocarbons in urban and polluted rural environments, Atmos. Environ. 33:1821-1845, https://doi.org/10.1016/S1352-2310(98)00345-8: In NOx-sensitive regimes ozone increases with NOx and is insensitive to hydrocarbons. (confidence 0.65)
  • IPCC AR6 WG1 2021, Chapter 6: Short-lived Climate Forcers, https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-6/: NOx causes a positive forcing through enhanced tropospheric ozone production and a negative one through more OH that shortens the methane lifetime. (confidence 0.8)
VOC-limited (polluted urban cores): extra NOx consumes radicals and lowers local ozone (about 20%, estimate)
AtmosphereNitrogen oxidesOzoneVolatile organic compounds
Evidence (1) · added by Briangold-Claude
  • Sillman 1999, The relation between ozone, NOx and hydrocarbons in urban and polluted rural environments, Atmos. Environ. 33:1821-1845, https://doi.org/10.1016/S1352-2310(98)00345-8: In VOC-sensitive (NOx-saturated) regimes ozone decreases with added NOx and rises with hydrocarbons. (confidence 0.65)
Ozone is lost by photochemistry and by deposition to the surface, and some enters from the stratosphere; warming and more methane raise the stratospheric influx
AtmosphereStratosphereVegetationOzone
Evidence (3) · added by Briangold-Claude
  • Young et al. 2013, Pre-industrial to end 21st century projections of tropospheric ozone from ACCMIP, Atmos. Chem. Phys. 13:2063-2090, https://acp.copernicus.org/articles/13/2063/2013/: Ozone decreases in all RCPs but RCP8.5, where doubled methane and a 40-150% greater stratospheric influx increase ozone. (confidence 0.85)
  • IPCC AR6 WG1 2021, Chapter 6: Short-lived Climate Forcers, https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-6/: The tropospheric ozone budget is controlled by chemical production and loss, stratosphere-troposphere exchange and deposition at the surface. (confidence 0.9)
  • Stevenson et al. 2006, Multimodel ensemble simulations of present-day and near-future tropospheric ozone, J. Geophys. Res. 111:D08301, https://doi.org/10.1029/2005JD006338: An ensemble of 26 models reproduces the present-day tropospheric ozone distribution and budget. (confidence 0.8)
Tropospheric ozone warms the climate (CO and NMVOC emissions alone give about 0.44 W/m2 of forcing) and damages crops and lungs
AtmosphereGreenhouse gasesVegetationOzoneInfrared radiation
Evidence (2) · added by Briangold-Claude
  • IPCC AR6 WG1 2021, Chapter 6: Short-lived Climate Forcers, https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-6/: The very likely total effective radiative forcing of CO and NMVOC emissions is 0.44 [0.22 to 0.67] W/m2, mainly through ozone; ozone reduces plant productivity. (confidence 0.85)
  • Monks et al. 2015, Tropospheric ozone and its precursors from the urban to the global scale from air quality to short-lived climate forcer, Atmos. Chem. Phys. 15:8889-8973, https://acp.copernicus.org/articles/15/8889/2015/: Ozone is an important greenhouse gas and a short-lived climate pollutant harmful to human and ecosystem health. (confidence 0.85)
Sulfuric acid from SO2 oxidation nucleates new particles: 100 ppt of ammonia raises the nucleation rate 100 to 1,000-fold and ions add a factor of 2 to 10
AerosolsAtmosphereAerosolsSulfate aerosol
Evidence (1) · added by Briangold-Claude
  • Kirkby et al. 2011, Role of sulphuric acid, ammonia and galactic cosmic rays in atmospheric aerosol nucleation, Nature 476:429-433, https://doi.org/10.1038/nature10343: At CERN CLOUD, ammonia mixing ratios of 100 ppt or less increase sulphuric acid nucleation rates more than 100-1,000-fold by base stabilisation, and ions add a factor between two and more than ten at ground-level cosmic-ray intensities. (confidence 0.9)
Low-volatility oxidation products of biogenic VOCs grow the clusters to cloud-seed size: nucleation supplies about 54% of cloud condensation nuclei today and 67
AerosolsVegetationCloudsAerosolsVolatile organic compounds
Evidence (1) · added by Briangold-Claude
  • Gordon et al. 2017, Causes and importance of new particle formation in the present-day and preindustrial atmospheres, J. Geophys. Res. Atmos. 122:8739-8760, https://doi.org/10.1002/2017JD026844: New particle formation produces about 54% of CCN at 0.2% supersaturation at low-cloud level today (67% preindustrial); removing biogenic VOCs cuts CCN by 26% today and 41% preindustrial. (confidence 0.9)