Quantification of fossil fuel CO ₂ from combined CO, δ¹³CO ₂ and Δ ¹⁴CO ₂ observations

We present a new method for partitioning observed COinline-formula₂ enhancements (COinline-formula₂xs) into fossil and biospheric fractions (inline-formulaC_ff and inline-formulaC_bio) based on measurements of CO and inline-formulaδ¹³COinline-formula₂, complemented by flask-based inline-formulaΔ¹⁴COinline-formula₂ measurements. This method additionally partitions the fossil fraction into natural gas and petroleum fractions (when coal combustion is insignificant). Although here we apply the method only to discrete flask air measurements, the advantage of this method (CO- and inline-formulaδ¹³COinline-formula₂-based method) is that COinline-formula₂xs partitioning can be applied at high frequency when continuous measurements of CO and inline-formulaδ¹³COinline-formula₂ are available. High-frequency partitioning of COinline-formula₂xs into inline-formulaC_ff and inline-formulaC_bio has already been demonstrated using continuous measurements of CO (CO-based method) and inline-formulaΔ¹⁴COinline-formula₂ measurements from flask air samples. We find that the uncertainty in inline-formulaC_ff estimated from the CO- and inline-formulaδ¹³COinline-formula₂-based method averages 3.2 ppm (23 % of the mean inline-formulaC_ff of 14.2 ppm estimated directly from inline-formulaΔ¹⁴COinline-formula₂), which is significantly less than the CO-based method which has an average uncertainty of 4.8 ppm (34 % of the mean inline-formulaC_ff). Using measurements of CO, inline-formulaδ¹³COinline-formula₂ and inline-formulaΔ¹⁴COinline-formula₂ from flask air samples at three sites in the greater Los Angeles (LA) region, we find large contributions of biogenic sources that vary by season. On a monthly average, the biogenic signal accounts for inline-formula−14 to inline-formula+25 % of COinline-formula₂xs with larger and positive contributions in winter and smaller and negative contributions in summer due to net respiration and net photosynthesis, respectively. Partitioning inline-formulaC_ff into petroleum and natural gas combustion fractions reveals that the largest contribution of natural gas combustion generally occurs in summer, which is likely related to increased electricity generation in LA power plants for air-conditioning.