Observations of OM/OC and specific attenuation coefficients (SAC) in ambient fine PM at a rural site in central Ontario, Canada

Abstract

Abstract. Ambient particulate matter (PM) samples were collected on quartz filters at a rural site in central Ontario during an intensive study in 2007. The concentrations of organic carbon (OC), pyrolysis organic carbon (POC), and elemental carbon (EC) were determined by thermal analysis. The concentrations are compared to the organic aerosol mass concentration (OM) measured with an Aerodyne C-ToF Aerosol Mass Spectrometer (AMS) and to the particle absorption coefficient (b asp ) obtained from a Radiance Research Particle Soot Absorption Photometer (PSAP). The total organic mass to organic carbon ratios (OM/OC) and specific attenuation coefficients (SAC=b asp /EC) are derived. Proportionality of the POC mass with the oxygen mass in the aerosols estimated from the AMS offers a potential means to estimate OM/OC from thermal measurements only. The mean SAC for the study is 3.8±0.3 m 2 g −1 . It is found that the SAC is independent of or decrease with increasing particle mass loading, depending on whether or not the data are separated between aerosols dominated by more recent anthropogenic input and aerosols dominated by longer residence time or biogenic components. There is no evidence to support an enhancement of light absorption by the condensation of secondary material to particles, suggesting that present model simulations built on such an assumption may overestimate atmospheric warming by BC.

Atmospheric Volatile Organic Compounds in a Typical Urban Area of Beijing: Pollution Characterization, Health Risk Assessment and Source Apportionment

“…According to studies, the calculated (OC/EC) min in spring, summer, autumn and winter was 1.34, 1.30, 0.91 and 1.03, respectively. Coef SOA/SOC was 1.4 in our study [23][24][25][26].…”

“…In the present study, OC and EC concentrations obtained from online (4) In Equation (4), TOC is the total organic carbon content of fine particles in the atmosphere; EC is the elemental carbon content in fine particles; (OC/EC) min is the measured minimum ratio of OC/EC; and Coef SOA/SOC is the conversion factor between SOAs and SOCs [24]. According to studies, the calculated (OC/EC) min in spring, summer, autumn and winter was 1.34, 1.30, 0.91 and 1.03, respectively.…”

The hygroscopicity parameter (κ) of ambient organic aerosol at a field site subject to biogenic and anthropogenic influences: relationship to degree of aerosol oxidation

“…Results from Chan et al (2010) for Egbert 2007 found that the ratio of elemental carbon to organic matter (EC/OM) for the study was 0.2 except for the final Biogenic periods, during which it decreased to 0.15. Case 9 considers the normal case in which the ratio is 0.2 and the extra EC mass is assumed to be non-hygroscopic with a density of 1800 kg m −3 .…”

“…The overall goal of Egbert 2007 was to improve our understanding of the sources and hygroscopicity of organic aerosols. To this end, recent publications from this campaign have shown that the oxidation state of the aerosol correlates with the photochemical age of the air ), significant secondary organic aerosol (SOA) mass can be formed from monoterpene oxidation , oxygenated organic aerosols from anthropogenicallyinfluenced air could have primary and secondary sources, while biogenically-influenced air only had secondary sources (Chan et al, 2010), and aerosols from anthropogenicallyinfluenced air showed a delay in cloud droplet activation compared to biogenically-influenced air . The present study focuses on the hygroscopicity of the organic component of the aerosol by performing an aerosol-CCN closure experiment alongside measurements of the organic component of the gas and particulate phases, so as to best define the source of air sampled at CARE.…”

Uncertainties in PM2.5 Gravimetric and Speciation Measurements and What We Can Learn from Them

“…[41][42][43][44][45][46][47][48][49][50][51][52][53] Turpin and Lim 41 concluded that a factor of about 1.6 would be appropriate for an urban organic aerosol, whereas a factor of 2.1 may be more appropriate for an aged, nonurban aerosol.…”