Time-resolved ambient particulate organic (OC) and elemental carbon (EC) data measured in Atlanta... more Time-resolved ambient particulate organic (OC) and elemental carbon (EC) data measured in Atlanta, GA, during the Atlanta Supersite Experiment (August3-September 1, 1999) were investigated to determine the temporal trends of atmospheric carbonaceous aerosol and to examine the relative contributions of primary and secondary OC to measured particulate OC. Mean 1-h average concentrations (ranges in parentheses) of PM2.5 OC, EC, and total carbon were 8.3 (3.6-15.8), 2.3 (0.3-9.6), and 10.6 (4.6-24.6) microg of C m(-3), respectively, based on Rutgers University/Oregon Graduate Institute in situ thermal-optical carbon analyzer measurements. Carbonaceous matter (organic material 40%; EC 8%) comprised approximately 48% of PM2.5 mass in Atlanta. Primary and secondary OC concentrations were estimated using an EC tracer method. Secondary OC contributed approximately 46% of measured particulate OC, and 1-h average contributions ranged up to 88%. Vehicle emissions appear to be the dominant contributors to measured EC and primary OC concentrations based on temporal patterns of EC, primary OC, and CO. This research suggests that secondary OC concentrations in Atlanta were influenced by (1) "fresh" secondary organic aerosol formed by photochemical reactions locally in the early afternoons as seen in the Los Angeles air basin and (2) "aged" secondary organic aerosol transported from upwind regions or formed on previous days. Nocturnal peaks in secondary OC and ozone concentrations were observed on several days. The most probable explanation for this is the favorable partitioning of semivolatile organic compounds to the particulate phase driven by temperature decreases and relative humidity increases at night and vertical transport of regional pollutants from above to ground level.
Isoprene accounts for more than half of non-methane volatile organics globally. Despite extensive... more Isoprene accounts for more than half of non-methane volatile organics globally. Despite extensive experimentation, homogeneous formation of secondary organic aerosol (SOA) from isoprene remains unproven. Herein, an incloud process is identified in which isoprene produces SOA. Interstitial oxidation of isoprene produces water-soluble aldehydes that react in cloud droplets to form organic acids. Upon cloud evaporation new organic particulate matter is formed. Cloud processing of isoprene contributes at least 1.6 Tg yr(-1) to a global biogenic SOA production of 8-40 Tg yr(-1). We conclude that cloud processing of isoprene is an important contributor to SOA production, altering the global distribution of hygroscopic organic aerosol and cloud condensation nuclei.
In virtually all published literature wherein closure between gravimetric and chemical measuremen... more In virtually all published literature wherein closure between gravimetric and chemical measurements is tested, the concentration of particulate organics is estimated by multiplying the measured concentration of organic carbon (micrograms carbon/cubic meter air) by a factor of 1.2-1.4. This factor, ...
Time-resolved ambient particulate organic (OC) and elemental carbon (EC) data measured in Atlanta... more Time-resolved ambient particulate organic (OC) and elemental carbon (EC) data measured in Atlanta, GA, during the Atlanta Supersite Experiment (August3-September 1, 1999) were investigated to determine the temporal trends of atmospheric carbonaceous aerosol and to examine the relative contributions of primary and secondary OC to measured particulate OC. Mean 1-h average concentrations (ranges in parentheses) of PM2.5 OC, EC, and total carbon were 8.3 (3.6-15.8), 2.3 (0.3-9.6), and 10.6 (4.6-24.6) microg of C m(-3), respectively, based on Rutgers University/Oregon Graduate Institute in situ thermal-optical carbon analyzer measurements. Carbonaceous matter (organic material 40%; EC 8%) comprised approximately 48% of PM2.5 mass in Atlanta. Primary and secondary OC concentrations were estimated using an EC tracer method. Secondary OC contributed approximately 46% of measured particulate OC, and 1-h average contributions ranged up to 88%. Vehicle emissions appear to be the dominant contributors to measured EC and primary OC concentrations based on temporal patterns of EC, primary OC, and CO. This research suggests that secondary OC concentrations in Atlanta were influenced by (1) "fresh" secondary organic aerosol formed by photochemical reactions locally in the early afternoons as seen in the Los Angeles air basin and (2) "aged" secondary organic aerosol transported from upwind regions or formed on previous days. Nocturnal peaks in secondary OC and ozone concentrations were observed on several days. The most probable explanation for this is the favorable partitioning of semivolatile organic compounds to the particulate phase driven by temperature decreases and relative humidity increases at night and vertical transport of regional pollutants from above to ground level.
Isoprene accounts for more than half of non-methane volatile organics globally. Despite extensive... more Isoprene accounts for more than half of non-methane volatile organics globally. Despite extensive experimentation, homogeneous formation of secondary organic aerosol (SOA) from isoprene remains unproven. Herein, an incloud process is identified in which isoprene produces SOA. Interstitial oxidation of isoprene produces water-soluble aldehydes that react in cloud droplets to form organic acids. Upon cloud evaporation new organic particulate matter is formed. Cloud processing of isoprene contributes at least 1.6 Tg yr(-1) to a global biogenic SOA production of 8-40 Tg yr(-1). We conclude that cloud processing of isoprene is an important contributor to SOA production, altering the global distribution of hygroscopic organic aerosol and cloud condensation nuclei.
In virtually all published literature wherein closure between gravimetric and chemical measuremen... more In virtually all published literature wherein closure between gravimetric and chemical measurements is tested, the concentration of particulate organics is estimated by multiplying the measured concentration of organic carbon (micrograms carbon/cubic meter air) by a factor of 1.2-1.4. This factor, ...
Time-resolved ambient particulate organic (OC) and elemental carbon (EC) data measured in Atlanta... more Time-resolved ambient particulate organic (OC) and elemental carbon (EC) data measured in Atlanta, GA, during the Atlanta Supersite Experiment (August3-September 1, 1999) were investigated to determine the temporal trends of atmospheric carbonaceous aerosol and to examine the relative contributions of primary and secondary OC to measured particulate OC. Mean 1-h average concentrations (ranges in parentheses) of PM2.5 OC, EC, and total carbon were 8.3 (3.6-15.8), 2.3 (0.3-9.6), and 10.6 (4.6-24.6) microg of C m(-3), respectively, based on Rutgers University/Oregon Graduate Institute in situ thermal-optical carbon analyzer measurements. Carbonaceous matter (organic material 40%; EC 8%) comprised approximately 48% of PM2.5 mass in Atlanta. Primary and secondary OC concentrations were estimated using an EC tracer method. Secondary OC contributed approximately 46% of measured particulate OC, and 1-h average contributions ranged up to 88%. Vehicle emissions appear to be the dominant contributors to measured EC and primary OC concentrations based on temporal patterns of EC, primary OC, and CO. This research suggests that secondary OC concentrations in Atlanta were influenced by (1) "fresh" secondary organic aerosol formed by photochemical reactions locally in the early afternoons as seen in the Los Angeles air basin and (2) "aged" secondary organic aerosol transported from upwind regions or formed on previous days. Nocturnal peaks in secondary OC and ozone concentrations were observed on several days. The most probable explanation for this is the favorable partitioning of semivolatile organic compounds to the particulate phase driven by temperature decreases and relative humidity increases at night and vertical transport of regional pollutants from above to ground level.
Isoprene accounts for more than half of non-methane volatile organics globally. Despite extensive... more Isoprene accounts for more than half of non-methane volatile organics globally. Despite extensive experimentation, homogeneous formation of secondary organic aerosol (SOA) from isoprene remains unproven. Herein, an incloud process is identified in which isoprene produces SOA. Interstitial oxidation of isoprene produces water-soluble aldehydes that react in cloud droplets to form organic acids. Upon cloud evaporation new organic particulate matter is formed. Cloud processing of isoprene contributes at least 1.6 Tg yr(-1) to a global biogenic SOA production of 8-40 Tg yr(-1). We conclude that cloud processing of isoprene is an important contributor to SOA production, altering the global distribution of hygroscopic organic aerosol and cloud condensation nuclei.
In virtually all published literature wherein closure between gravimetric and chemical measuremen... more In virtually all published literature wherein closure between gravimetric and chemical measurements is tested, the concentration of particulate organics is estimated by multiplying the measured concentration of organic carbon (micrograms carbon/cubic meter air) by a factor of 1.2-1.4. This factor, ...
Time-resolved ambient particulate organic (OC) and elemental carbon (EC) data measured in Atlanta... more Time-resolved ambient particulate organic (OC) and elemental carbon (EC) data measured in Atlanta, GA, during the Atlanta Supersite Experiment (August3-September 1, 1999) were investigated to determine the temporal trends of atmospheric carbonaceous aerosol and to examine the relative contributions of primary and secondary OC to measured particulate OC. Mean 1-h average concentrations (ranges in parentheses) of PM2.5 OC, EC, and total carbon were 8.3 (3.6-15.8), 2.3 (0.3-9.6), and 10.6 (4.6-24.6) microg of C m(-3), respectively, based on Rutgers University/Oregon Graduate Institute in situ thermal-optical carbon analyzer measurements. Carbonaceous matter (organic material 40%; EC 8%) comprised approximately 48% of PM2.5 mass in Atlanta. Primary and secondary OC concentrations were estimated using an EC tracer method. Secondary OC contributed approximately 46% of measured particulate OC, and 1-h average contributions ranged up to 88%. Vehicle emissions appear to be the dominant contributors to measured EC and primary OC concentrations based on temporal patterns of EC, primary OC, and CO. This research suggests that secondary OC concentrations in Atlanta were influenced by (1) "fresh" secondary organic aerosol formed by photochemical reactions locally in the early afternoons as seen in the Los Angeles air basin and (2) "aged" secondary organic aerosol transported from upwind regions or formed on previous days. Nocturnal peaks in secondary OC and ozone concentrations were observed on several days. The most probable explanation for this is the favorable partitioning of semivolatile organic compounds to the particulate phase driven by temperature decreases and relative humidity increases at night and vertical transport of regional pollutants from above to ground level.
Isoprene accounts for more than half of non-methane volatile organics globally. Despite extensive... more Isoprene accounts for more than half of non-methane volatile organics globally. Despite extensive experimentation, homogeneous formation of secondary organic aerosol (SOA) from isoprene remains unproven. Herein, an incloud process is identified in which isoprene produces SOA. Interstitial oxidation of isoprene produces water-soluble aldehydes that react in cloud droplets to form organic acids. Upon cloud evaporation new organic particulate matter is formed. Cloud processing of isoprene contributes at least 1.6 Tg yr(-1) to a global biogenic SOA production of 8-40 Tg yr(-1). We conclude that cloud processing of isoprene is an important contributor to SOA production, altering the global distribution of hygroscopic organic aerosol and cloud condensation nuclei.
In virtually all published literature wherein closure between gravimetric and chemical measuremen... more In virtually all published literature wherein closure between gravimetric and chemical measurements is tested, the concentration of particulate organics is estimated by multiplying the measured concentration of organic carbon (micrograms carbon/cubic meter air) by a factor of 1.2-1.4. This factor, ...
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