Unexpected changes in source apportioned results derived from different ambient VOC metrics

Area of Science:

• Environmental Chemistry
• Atmospheric Science
• Air Pollution Research

Background:

• Volatile organic compounds (VOCs) are key precursors to ozone pollution.
• Most VOC source apportionment studies use mixing ratios, but a significant portion (23%) use mass concentrations.
• Differences in metric choices can impact the accuracy of source apportionment and control strategy development.

Purpose of the Study:

• To investigate the impact of using mass concentrations versus volumetric concentrations on VOC source apportionment.
• To assess how metric differences affect the identification and contribution of different VOC sources.
• To determine which metric provides more practical significance for air pollution control.

Main Methods:

• Collected hourly VOC volumetric concentrations in three Chinese cities.
• Converted volumetric concentrations to mass concentrations under standard and actual temperature-pressure conditions.
• Applied positive matrix factorization (PMF) to both volumetric (VC-PMF) and mass concentration (MC-PMF) data.

Main Results:

• Mass concentration data analysis (MC-PMF) led to decreased concentrations of low relative molecular mass (RMM) VOCs and increased concentrations of high RMM VOCs compared to volumetric data (VC-PMF).
• No substantial differences were found between source apportionments using standard versus actual condition mass concentrations.
• Significant differences in the ranking of source contributions were observed between volumetric and mass data analyses.

Conclusions:

• The choice of metric (volumetric vs. mass concentration) significantly alters VOC source apportionment results, particularly affecting the relative contributions of sources emitting low vs. high RMM species.
• Mass concentration data analyses can misrepresent source contributions, potentially hindering effective control strategy development.
• Volumetric concentration data provides more practical significance for developing targeted air pollution control strategies for VOCs.