Mark Gibson | Dalhousie University (original) (raw)

Papers by Mark Gibson

Ground-based observations have insufficient spatial coverage to assess long-term human exposure t... more Ground-based observations have insufficient spatial coverage to assess long-term human exposure to fine particulate matter (PM 2.5 ) at the global scale. Satellite remote sensing offers a promising approach to provide information on both short-and long-term exposure to PM 2.5 at local-toglobal scales, but there are limitations and outstanding questions about the accuracy and precision with which groundlevel aerosol mass concentrations can be inferred from satellite remote sensing alone. A key source of uncertainty is the global distribution of the relationship between annual average PM 2.5 and discontinuous satellite observations of columnar aerosol optical depth (AOD). We have initiated a global network of ground-level monitoring stations designed to evaluate and enhance satellite remote sensing estimates for application in health-effects research and risk assessment. This Surface PARTiculate mAtter Network (SPARTAN) includes a global federation of ground-level monitors of hourly PM 2.5 situated primarily in highly populated regions and collocated with existing ground-based sun photometers that measure AOD. The instruments, a three-wavelength nephelometer and impaction filter sampler for both PM 2.5 and PM 10 , are highly autonomous. Hourly PM 2.5 concentrations are inferred from the combination of weighed filters and nephelometer data. Data from existing networks were used to develop and evaluate network sampling characteristics. SPARTAN filters are analyzed for mass, black carbon, watersoluble ions, and metals. These measurements provide, in a variety of regions around the world, the key data required to evaluate and enhance satellite-based PM 2.5 estimates used for assessing the health effects of aerosols. Mean PM 2.5 concentrations across sites vary by more than 1 order of magnitude. Our initial measurements indicate that the ratio of AOD to ground-level PM 2.5 is driven temporally and spatially by the vertical profile in aerosol scattering. Spatially this ratio is also strongly influenced by the mass scattering efficiency.

Indoor air concentrations of formaldehyde, acetaldehyde and acrolein were measured in Halifax, No... more Indoor air concentrations of formaldehyde, acetaldehyde and acrolein were measured in Halifax, Nova Scotia and Edmonton, Alberta. Seven consecutive 24-hr measurements were made in 50 non-smoking homes in winter and summer in each city. In addition, data on relative humidity, temperature, air exchange rates, housing characteristics and occupants' activities were collected. Determinants of indoor levels for formaldehyde and acetaldehyde were examined using linear mixed-effects regression models. The housing characteristics and occupants' activities investigated in this study explained between 26% and 50% of the variability in pollutant concentrations, with air exchange rates, year of construction, indoor temperature and indoor relative humidity being important predictors for both formaldehyde and acetaldehyde.

A method using ultrasonication extraction and solid phase extraction (SPE) clean-up for determina... more A method using ultrasonication extraction and solid phase extraction (SPE) clean-up for determination of US EPA 16 priority pollutant polycyclic aromatic hydrocarbons (PAHs) in soils by reversed-phase liquid chromatography (RP-LC) with ultraviolet (UV) absorption detection was studied. Separation and detection of the 16 PAHs were completed in 31 min by RP-LC with a C 18 column (Bakerbond PAH 6 PLUS 125Â3.0 i.d. mm or Phenomenex ENVIROSEP-PP 125Â3.2 i.d. mm), acetonitrile± water gradient elution and UV absorption detection. The detection limits, for a 10 ml of solution injection, determined at 254 nm were less than 1 mg/ml, except for acenaphthene, which was 1.05 mg/ml. Because individual PAHs are present in soils at the ng/g level or below and few sample matrices can be analyzed directly without serious interference, ef®cient extraction, preconcentration and clean-up of PAHs from the samples are indispensable prior to the determination of the PAHs. Several organic solvents were tested for extraction of the PAHs from soils, and ultrasonication extraction was used for the extraction in acetone of the 16 PAHs in soils. Several SPE procedures were tested and compared, and Supelco 6 ml LC-18 SPE cartridge and acetone:tetrahydrofuran (THF)1:1 eluant were used for the preconcentration and clean-up of the 16 PAHs in the soil. The method was successfully applied to determine the 16 PAHs in the soil sampled from an industrial land in the UK. # 1998 Elsevier Science B.V.

h i g h l i g h t s < Spatiotemporal variation of NO 2 and SO 2 in a pristine Canadian National P... more h i g h l i g h t s < Spatiotemporal variation of NO 2 and SO 2 in a pristine Canadian National Park. < SO 2 associated with elevated sites within the Park. < Significant spatial patterns observed for NO 2 in the Park. < Significant seasonal difference observed for NO 2 but not for SO 2 . < Significant predictors of the index of air purity were determined.

Concurrent 24-hr samples of particulate matter of median aerodynamic diameter less than 10 m (PM ... more Concurrent 24-hr samples of particulate matter of median aerodynamic diameter less than 10 m (PM 10 ) were collected over a 10-day period in August 2000 at four sites along a transect in west-central Scotland, UK (passing from the coast through the city of Glasgow) in line with the prevailing southwesterly wind. Each sample was analyzed for chloride (Cl Ϫ ), nitrate (NO 3 Ϫ ), sulfate (SO 4 2Ϫ ), ammonium (NH 4 ϩ ), calcium (Ca 2ϩ ), iron (Fe), and organic hydrocarbon material (OHM). The contribution from elemental carbon (EC) was estimated. Sampling days were categorized according to local wind direction, synoptic flow, and air mass back trajectories. Chemical mass balance (CMB) reconstruction of the following PM 10 components was derived for each wind direction group and at each transect location: ammonium sulfate ((NH 4 ) 2 SO 4 ), ammonium nitrate (NH 4 NO 3 ), sodium chloride (NaCl), gypsum (CaSO 4 ), OHM, EC, soil/surface dusts, and particle-bound water. The results showed that PM 10 at the coastal site was dominated by the marine background (NaCl) compared with the urban sites, which were dominated by local primary (EC and soil/resuspension) and