Application of the PTM-MCM to the TORCH-1 campaign Steve Utembe, Mike Jenkin and David Johnson EPSR Group Department of Environmental Science and Technology

Studies using the PTM Chemical development of air parcels arriving at Writtle site investigated, at six-hourly resolution for the entire campaign hours back trajectories obtained from NOAA Chemical processing using CRI mechanism Additional analysis of selected trajectories using MCM v3.1

Brief description of the PTM 4-day back trajectory VOC and NO X sunlight chemistry and transport emissions calculate ozone along pre-selected trajectories over Europe well-mixed boundary layer box

Emissions UK anthropogenic emissions based on NAEI. Anthropogenic emissions outside UK based on EMEP. Biogenic VOC emissions based on Simpson (1995). Idealised seasonal, weekly and diurnal variations applied. NMVOC emissions speciation based on NAEI for ca. 70% of total. Remaining 30% assigned to surrogates for which chemistry treated.

Emissions speciation: 124 anthropogenic NMVOC alkanesalkenes carbonyls alcoholsethersestersaromaticsacidschloro- carbons fraction of total butane ethanol toluene

Ozone: observed vs calculated

Ozone observed vs calculated : sensitivity to trajectory height

Emitted aromatic hydrocarbon: toluene

Emitted aromatic hydrocarbons

Emitted alkyne: acetylene

Emitted alkanes

Emitted cycloalkane: cyclohexane (used as a surrogate for all emitted cycloalkanes)

Emitted alkenes and dienes

Emitted biogenic hydrocarbon: isoprene

Mean hydrocarbon concentrations

Aldehyde with primary and secondary sources: HCHO preliminary HCHO measurements made by UEA

Simulated aldehyde product distributions on 3 example trajectories (N.B. we have simulated concentration data on 1257 carbonyl compounds)

Simulated ketone product distributions on 3 example trajectories

Concentrations of selected carbonyl products from aromatics

Concentrations of selected carbonyl products from biogenics

Organic nitrates and relationship to precursor peroxy radicals Ozone and organic nitrates are both produced from reaction of peroxy radicals with NO RO 2 + NO [ROONO]* RO. + NO 2 (R1) + M RONO 2 (R2) Correlation between the concentration of the two [RO 2 ] i  [RONO 2 ] i /  i where  i = k1/k2

Comparison of relative concentrations of RO 2 radicals produced from reactions of OH with alkanes and alkenes (O’Brien et al. 1995) Alkyl peroxy RO 2 ’s  -hydroxy 24 hours chemical processing

Concentrations at end of day 5 for a series of alkyl and  - hydroxyalkyl peroxy radicals calculated with the MCM/PTM show similar distribution of peroxy radicals inferred from the organic nitrate observations of O'Brien et al.  -hydroxy 5 days chemical processing Alkyl peroxy RO2’s

Concentration distribution of C1-C5 alkyl nitrates in MCM3.1

Concentration distribution of C2-C4  -hydroxy alkyl nitrates in MCM3.1

Identifying top contributors to total carbonyl distribution in MCM v3.1 There are 1257 carbonyls in MCM v3.1(!) What are the dominant carbonyls in air masses of different degrees of photochemical processing?

Top contributors to 90% of total carbonyl concentration Least photochemically processed Intermediate Most photochemically processed HCHO CH3COCH3 HCHO MEK CH3CHO MEK CH3CHO

Concluding remarks Simulation of TORCH-1 campaign using PTM-CRI has allowed emitted VOC speciation to be tested. Simulated and observed hydrocarbon concentrations were generally well correlated. Simulated concentrations of 6 aromatics, acetylene, 1,3-butadiene and intermediate alkanes were in very good agreement with observations. Simulated concentrations of alkenes and small alkanes tended to be slightly lower than observations. Simulated concentrations of larger alkanes were generally greater than those observed: this mainly due to ‘surrogate’ contributions. MCM allows study of distributions of concentrations of various classes of VOCs