Quantification of source specific black carbon scavenging using an aethalometer and a disdrometer

Area of Science:

• Atmospheric Science
• Environmental Science
• Climate Science

Background:

• Aerosol black carbon (BC) is a potent climate warming agent and poses health risks.
• Understanding BC removal processes, like rain scavenging, is crucial for climate and air quality assessments.

Purpose of the Study:

• To quantify the scavenging efficiency of aerosol black carbon (BC) by rainfall.
• To investigate the influence of rain characteristics and BC source on scavenging rates.
• To develop a model for estimating BC reduction during precipitation events.

Main Methods:

• A 15-month sampling campaign in León, Spain, utilizing an ensemble aethalometer-disdrometer.
• Measurement of equivalent black carbon (eBC) concentrations and raindrop size distributions.
• Analysis of 75 rain events, correlating scavenging coefficients with rain duration, BC source (fossil fuel vs. biomass burning), and meteorological data.

Main Results:

• Effective BC scavenging occurred in 73% of rain events, with mean reductions of 48% (long events) and 39% (short events).
• Scavenging coefficients varied significantly with BC source and rain duration, with higher rates for biomass burning BC and short rain events.
• A positive correlation was found between scavenging and raindrop size (0.375–2.5 mm), and effective scavenging was observed for various air mass origins.
• A linear model (R² = 0.72) was developed to predict BC reduction using eBC concentration, swept volume, and precipitation data.

Conclusions:

• Rainfall is an effective mechanism for removing aerosol black carbon from the atmosphere.
• BC scavenging efficiency is influenced by its emission source and the dynamics of the rainfall event.
• The developed model provides a valuable tool for estimating BC removal during precipitation, aiding climate and air quality studies.