Ozone Formation Potential (OFP)

Ozone Formation Potential (OFP) evaluates the contribution of volatile organic compounds (VOCs) to tropospheric ozone formation.

Basic Principles

VOCs react with NOx under sunlight to form ozone:

\[VOC + NO_x + h\nu \rightarrow O_3 + \text{products}\]

Different VOCs have vastly different reactivities, so quantifying the relative contribution of each species is necessary.

Maximum Incremental Reactivity (MIR)

Definition

MIR (Maximum Incremental Reactivity) represents the amount of ozone produced per unit mass of VOC under optimal conditions:

\[MIR_i = \frac{\partial [O_3]}{\partial [VOC_i]}_{max}\]

Units: g O3 / g VOC

Typical MIR Values

VOC Species	MIR (g O3/g VOC)	Reactivity Class
Methane	0.014	Very low
Ethane	0.28	Low
Propane	0.49	Low
Ethylene	9.00	High
Propylene	11.66	High
Toluene	4.00	Medium
Xylene	7.80	High
Formaldehyde	9.46	High
Isoprene	10.61	High

OFP Calculation

Single Species

\[OFP_i = C_i \times MIR_i\]

Where: - \(C_i\) = Concentration of species i (ug/m3) - \(MIR_i\) = MIR value of species i

Total OFP

\[OFP_{total} = \sum_i C_i \times MIR_i\]

Secondary Organic Aerosol Potential (SOAP)

Definition

SOAP (Secondary Organic Aerosol Potential) evaluates the ability of VOCs to form secondary organic aerosol:

\[SOAP_i = C_i \times SOAP_{factor,i}\]

Typical SOAP Factors

VOC Species	SOAP Factor	Description
Benzene	1.0	Reference species
Toluene	2.7	Moderate SOA formation
Xylene	5.5	High SOA formation
alpha-Pinene	32	Very high (biogenic)
Isoprene	2.4	Biogenic

VOC Reactivity Classification

By Chemical Category

Category	Typical Reactivity	Representative Species
Alkanes	Low-Medium	Ethane, Propane, Butane
Alkenes	High	Ethylene, Propylene, Butene
Aromatics	Medium-High	Benzene, Toluene, Xylene
Aldehydes	High	Formaldehyde, Acetaldehyde
Terpenes	Very High	Isoprene, alpha-Pinene

AeroViz Implementation

from AeroViz import voc_potentials

# Calculate OFP and SOAP
result = voc_potentials(df_voc)

# Output: dict with keys 'Conc', 'OFP', 'SOAP', 'LOH' (each a DataFrame)
result['OFP']           # OFP per species (ug O3/m3)
result['SOAP']          # SOAP per species
# Each frame also has per-class '*_total' columns and a grand 'Total' column:
result['OFP']['Total']  # total OFP across all species (a time-indexed Series)

Input Format

# Columns are VOC species names
df_voc.columns = ['Benzene', 'Toluene', 'Ethylbenzene', 'm,p-Xylene', 'o-Xylene', ...]

# Units: ppb or ug/m3

Supported Species

See support_voc.json, including: - Alkanes (C2-C12) - Alkenes (C2-C6) - Aromatics (BTEX, etc.) - Halogenated hydrocarbons - Oxygenated VOCs (OVOCs)

Applications

Source Identification: Different sources have distinct VOC compositions and OFP characteristics
Control Strategies: Prioritize controlling high-reactivity VOCs
Ozone Prediction: Estimate the impact of VOC emission reductions on ozone levels

References

Carter, W. P. L. (2010). Development of the SAPRC-07 chemical mechanism. Atmos. Environ., 44(40), 5324-5335.
Derwent, R. G., et al. (2010). Photochemical ozone creation potentials (POCPs) for different emission sources of organic compounds under European conditions estimated with a Master Chemical Mechanism. Atmos. Environ., 41(12), 2570-2579.