Jeffrey S. Gaffney

Particulate Air Pollution in Mexico City: A Collaborative Research Project

PM10, PM25, precursor gas, and upper-air meteorological measurements were taken in Mexico City, Mexico, from February 23 to March 22, 1997, to understand concentrations and chemical compositions of the citys particulate matter (PM). Average 24-hr PM10 concentrations over the period of study at the core sites in the city were 75 H g/m3. The 24-hr standard of 150 μ g/m3 was exceeded for seven samples taken during the study period; the maximum 24-hr concentration measured was 542 μ g/m3. Nearly half of the PM10 was composed of fugitive dust from roadways, construction, and bare land. About 50% of the PM10 consisted of PM2.5, with higher percentages during the morning hours. Organic and black carbon constituted up to half of the PM2.5. PM concentrations were highest during the early morning and after sunset, when the mixed layers were shallow. Meteorological measurements taken during the field campaign show that on most days air was transported out of the Mexico City basin during the afternoon with little day-to-day carryover.

Beyond acid rain

This paper discussed the effects of the interactions of soluble oxidants and organic toxins with sulfur dioxide and nitrogen dioxide. It suggested that these chemical reactions in the atmosphere produced a more potent acid rain which was harmful not only because it had a low pH but because it contained oxidants and organic toxins which were harmful to surface vegetation and the organisms found in surface waters. It was stressed that air pollution is a global problem and that is is necessary to develop a better fundamental understanding of how air pollution is causing damage to the streams and forests of the world. 50 references.

An Empirical Method for the Determination of the Complex Refractive Index of Size-Fractionated Atmospheric Aerosols for Radiative Transfer Calculations

To adequately assess the effects of atmospheric aerosols on climate, their optical constants (scattering and absorption coefficients) must be known. The absorption and scattering coefficients of the aerosols are derived from the real and imaginary parts of the complex refractive index and are dependent on their size and chemical composition. Because aerosol properties vary significantly with location, it is difficult to assign values for the absorption and scattering of solar radiation by aerosols in models of global climate change. This study reports a new method of collecting size-fractionated atmospheric aerosol samples for the purpose of directly measuring their transmission and reflectance spectra followed by the determination of the complex refractive index across the entire atmospherically relevant spectral range. The samples were collected with a modified Sierra high-volume cascade impactor with the usual filter collection surfaces replaced with Teflon sheets machined to hold quartz (ultraviolet [UV]/visible transparent) and/or silver chloride (infrared transparent) sample collection plates. Reflectance and transmission spectra can be obtained on the aerosol samples directly as a function of wavelength, from 280 nm to 2.5 m, with an integrating sphere coupled to an UV/visible or a Fourier transform infrared (FTIR) spectrophotometer. The effective real and imaginary components of the refractive index of the bulk sample material can then be approximated, as a function of wavelength, from the sample spectra. Preliminary results are presented for carbon soot samples generated in the laboratory and for standard diesel soot samples in the UV/visible spectral range. These are compared to results obtained for size-fractionated atmospheric aerosol samples collected near Pasco, WA, West Mesa, AZ, and Argonne, IL.

Peroxyacyl Nitrates (PANs): Their Physical and Chemical Properties

Peroxyacyl nitrates (PANs) are important organic indicators of tropospheric chemical processes. In this chapter, our current understanding of the chemical and physical properties of PANs are reviewed.

Non‐methane hydrocarbons in the Arctic atmosphere at Barrow, Alaska

C2-C8 non-methane hydrocarbons (NMHCs) were detected in the arctic atmosphere at Barrow, Alaska, during seven sampling periods in March 1989. The most prominent NMHCs were ethene, acetylene, ethane, propane, and benzene. The concentrations and distribution of these species were similar to those observed at the same location in 1982 and in the Norwegian Arctic in 1983. The distribution of NMHCs in background arctic air during this period was similar to that of aged urban air. These findings provide additional evidence that NMHCs in the arctic atmosphere during spring may originate from industrialized mid-latitude regions and contribute to the arctic haze phenomenon.

Field observations of regional and urban impacts on NO2, ozone, UVB, and nitrate radical production rates in the Phoenix air basin

Abstract In the May and June of 1998, field measurements were taken at a site near the Usery Pass Recreation Area, ∼27 miles from the downtown Phoenix area, overlooking Phoenix and Mesa, Arizona. This site was selected to examine the impacts of the Phoenix urban plume on the Usery Pass Recreation Area and surrounding regions. Data were obtained for ultraviolet-B (UVB) radiation, nitrogen dioxide (NO 2 ), peroxyacetyl nitrate (PAN), ozone (O 3 ), and carbon monoxide (CO). Nocturnal plumes of NO 2 (in tens of ppb), observed near midnight, were correlated with CO and anti-correlated with O 3 . This behavior was consistent with the titration of locally generated NO by boundary layer O 3 to form the nighttime NO 2 plumes that were subsequently transported into the Usery Pass Recreation area. Nitrate radical (NO 3 ) production rates were calculated to be very high on the edges of these nocturnal plumes. Examination of O 3 and PAN data also indicates that Phoenix is being affected by long-range transport of pollutants from the Los Angeles to San Diego areas. A regional smoke episode was observed in May, accompanied by a decrease in UVB of factor of two and a decrease in O 3 and an increase in methyl chloride. Low level back trajectories and chemical evidence confirm that the smoke event originated in northern Mexico and that the reduced O 3 levels observed at Usery Pass could be partially due to reduced photolysis rates caused by carbonaceous soot aerosols transported in the smoke plume. The results are discussed with regard to potential effects of local pollution transport from the Phoenix air basin as well as an assessment of the contributions from long-range transport of pollutants to the background levels in the Phoenix-Usery Pass area.

Heterogeneous NOx chemistry in the polluted PBL

Abstract The significance of heterogeneous mechanisms in controlling gas-phase NO x (NO, NO 2 ) mixing ratios in polluted urban air, especially during nighttime, is not well established. Several recent studies have suggested that carbon soot can provide an effective surface for mediating the inter conversion among several NO y members. However, a number of such reactions reported in the literature have widely varying reaction probabilities and often conflicting pathways. We evaluated several of these reactions and choose the NO 2 conversion to HONO on the surface of soot particles for further analysis with a box photochemical model. These calculations show that the conversion of NO 2 to HONO on particle surfaces produces a large, measurable signal (up to several parts per billion) in nighttime HONO mixing ratios. Inclusion of this reaction was also shown to have significant impacts on ozone, OH and HO 2 in the polluted planetary boundary layer (PBL). The sensitivity of these results to the different reaction rate probabilities ( γ ) and particle surface areas was also examined. Results are then evaluated to find the combination of γ and surface areas that would mostly likely occur in the PBL within the limitations of the model.

Fast gas chromatography with luminol chemiluminescence detection for the simultaneous determination of nitrogen dioxide and peroxyacetyl nitrate in the atmosphere

An instrument has been designed and constructed for the simultaneous determination of nitrogen dioxide (NO2) and peroxyacetyl nitrate (PAN) in atmospheric samples. The instrument’s design is based on separation by fast gas chromatography (GC) with a 30 ft capillary column (DB-1) followed by detection by luminol chemiluminescence. The chemiluminescent reaction between NO2 or PAN and luminol takes place at the gas–liquid interface on the surface of a solid support. The chemiluminescent emission at 425 nm is detected with a photon counting module. The instrument is controlled by a 1.8 GHz Notebook computer with a WINDOWS 2000 operating system and a custom software application programmed in LABVIEW. Detection limits are in the low parts per trillion (ppt) with a time resolution of 30 s to 1 min. The instrument was operated during the Mexico City Metropolitan Area/Mexico City Megacity 2003 collaborative air quality study. Results for NO2 from this fast GC method were compared with results from a co-located dif...

Chemical characterization of size-fractionated humic and fulvic materials in aqueous samples

Abstract Humic and fulvic acids have been shown to be potentially important transport agents for inorganic and organic contaminants, including radionuclides, in surface and groundwaters. In this work, the possibility of characterizing humic and fulvic materials in the colloidal and macromolecular size ranges (i.e., between 3000 molecular weight (1 nm) and 0.45 μm) after size fractionation and collection with hollow-fiber ultrafilters has been investigated. Three surface waters have been examined as test cases. Using ultrafiltration, sized samples of humic and fulvic acids were chemically characterized with 13 C-nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR) using diffuse reflectance, and pyrolysis/gas chromatography (GC). These test cases demonstrate that sufficient material can be obtained by ultrafiltration with minimal or no alteration to the materials. In addition, inorganic analyses performed on the size fractions show that ultrafiltration can also allow the binding capacity of the humic materials in each fraction to be measured. Substantial variability among the different humic and fulvic fractions demonstrates the importance of sizing submicron materials in attempts to understand the mechanisms of pollutant transport by natural humic materials.

Chemiluminescent reactions of peroxyacetyl nitrate and ozone with triethylamine. Possible atmospheric monitor for peroxyacetyl nitrate.

H Chemiluminescence spectra from the gas phase reactions of peroxyacetyl nitrate (PAN) ( A max 650 nm) and ozone ( A max 520 nm) with triethylamine have been obtained a t atmospheric pressure. The two chemiluminescent reactions are easily distinguishable by optical filters. Concentrations of PAN as low as 6 ppb were detected by this chemiluminescence technique. The application of this method as an atmospheric monitor for PAN is discussed.