A question of importance for urban planning and attainment of air quality standards is how pollutant concentrations scale with city population. This study uses measurements of light absorption and ...light scattering coefficients as proxies for primary (i.e., black carbon aerosols) and total pollutant concentration to start addressing the relationship between per capita air pollutant concentration and city population. Analyses of aerosol light scattering and absorption measurements in suburban Mexico City, Mexico; Las Vegas, Nevada; Reno, Nevada; Beijing, China; and Delhi, India, suggest that common air pollutant concentrations scale approximately as the square root of the urban population, which is consistent with a simple 2D box model. This simple scaling relationship for per capita air pollution concentration might be useful both as a guide for comparing cities as well as for preparing for future projections of increased urbanization, especially for cities having more than 10 million inhabitants.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A combination of the finite‐difference time domain technique and a ray‐by‐ray integration method has been applied to compute the extinction efficiency and single‐scattering albedo for various size ...distributions associated with nonspherical ice crystals in laboratory and natural cirrus clouds. The two methods are applicable to small and large size parameters, respectively. The results obtained by the two methods converge when effective size parameters are larger than about 6. For laboratory ice crystals the overall features of the computed extinction efficiency are in general agreement with those determined from measurements. In particular, significant extinction windows at 2.85 and 10.5 μm, associated with the Christiansen effect, are observed in both theoretical and experimental results. These extinction minima appear because the real part of the refractive index approaches unity, so that absorption dominates light attenuation. The single‐scattering albedos at the two Christiansen spectral regions are found to be smaller than 0.5 for the laboratory ice crystals. The contours of extinction efficiency and single‐scattering albedo versus wavelength and particle size show that the magnitude of the Christiansen effect is dependent on particle size. For large ice crystals, the extinction windows are not significant because the extinction efficiency converges to its asymptotic value of 2, regardless of size parameters. For a number of size distributions observed during FIRE II IFO, the Christiansen effect is small. However, for cold cirrus, the extinction efficiencies in the Christiansen bands are approximately one half of the values at nearby wavelengths due to a significant number of small ice crystals that are present in cold cirrus clouds. It is concluded that the Christiansen effect must be accounted for in the determination of the extinction efficiency and the single‐scattering albedo for small ice particles in order to obtain a reliable optical depth and emissivity for cirrus clouds at infrared wavelengths. Finally, we show that using spherical particles with Mie theory is inadequate to explain the extinction measurements.
A resurgence of interest has arisen lately in the use of reciprocal nephelometers in aerosol instrumentation that also measures other optical properties such as extinction by the cavity ringdown ...method and absorption by the photoacoustic method. This paper provides fresh insight into these nephelometers from perspectives of instrument component evaluation, intra-instrument comparison and basic calibration. In particular, a 4 deg truncation angle reciprocal integrating nephelometer (IN) is described and demonstrated. An experimental setup for the measurement of the IN sensor cosine response is developed and described. To calibrate the IN, the sampling volume can be filled with an aerosol with negligible light absorption (e.g., ammonium sulfate), and scattering and extinction coefficients are monitored simultaneously. The performance of the IN is evaluated, at a wavelength of 532 nm, through extensive comparison with a 1 deg truncation angle integrating sphere integrating nephelometer (ISIN) that operates at the same wavelength. The intercomparison included measurements of ambient aerosol, kerosene soot, ammonium sulfate aerosol, NaCl aerosol and CO2 gas. Results of a linear regression analysis indicate an agreement between the IN and the ISIN within +/-8%. The main advantages of the IN over the ISIN are its fast time response, relatively large signal-to-noise (S/N) ratio and design simplicity.
Results from six continuous and semicontinuous black carbon (BC) and elemental carbon (EC) measurement methods are compared for ambient samples collected from December 2003 through November 2004 at ...the Fresno Supersite in California. Instruments included a multi-angle absorption photometer (MAAP; λ = 670 nm); a dual-wavelength (λ = 370 and 880 nm) aethalometer; seven-color (λ = 370, 470, 520, 590, 660, 880, and 950 nm) aethalometers; the Sunset Laboratory carbon aerosol analysis field instrument; a photoacoustic light absorption analyzer (λ = 1047 nm); and the R&P 5400 ambient carbon particulate monitor. All of these acquired BC or EC measurements over periods of 1 min to 1 hr. Twenty-four-hour integrated filter samples were also acquired and analyzed by the Interagency Monitoring of Protected Visual Environments (IMPROVE) thermal/optical reflectance carbon analysis protocol. Site-specific mass absorption efficiencies estimated by comparing light absorption with IMPROVE EC concentrations were 5.5 m
2
/g for the MAAP, 10 m
2
/g for the aethalometer at a wavelength of 880 nm, and 2.3 m
2
/g for the photoacoustic analyzer; these differed from the default efficiencies of 6.5, 16.6, and 5 m
2
/g, respectively. Scaling absorption by inverse wavelength did not provide equivalent light absorption coefficients among the instruments for the Fresno aerosol measurements. Ratios of light absorption at 370 nm to those at 880 nm from the aethalometer were nearly twice as high in winter as in summer. This is consistent with wintertime contributions from vehicle exhaust and from residential wood combustion, which is believed to absorb more shorter-wavelength light. To reconcile BC and EC measurements obtained by different methods, a better understanding is needed of the wavelength dependence of light-absorption and mass-absorption efficiencies and how they vary with different aerosol composition.
Aircraft observations of cirrus cloud were made near Coffeyville, Kansas, during November 1991 as part of the First ISCCP Regional Experiment II (FIRE II) project. Cloud ice particle spectra ...measurements were made using both a particle measuring system (PMS) 2DC probe and an ice particle replicator. Particles larger than 200 micrometers were column rosettes. The replicator shows the presence of large numbers of ice crystals smaller than 66 micrometers (two PMS size bins) that are not recorded by the PMS 2DC probe. Calculations based on the replicator data of the geometrical blocked area and absorption cross section of the cloud per unit volume show that small particles can contribute significantly to and sometimes dominate both the solar extinction and the infrared emission. Intercomparison is made of the ice particle size, area, and mass distributions determined by these different instruments. Power law relationships for area occluded by a crystal as a function of crystal maximum dimension were computed from the PMS 2DC data. The wavelength-dependent infrared absorption cross section per volume was computed using a simple model based on anomalous diffraction and area and mass dimensional relationships for the ice crystals.
Quantitative and selective labelling of proteins is widely used in both academic and industrial laboratories, and catalytic labelling of proteins using transpeptidases, such as sortases, has proved ...to be a popular strategy for such selective modification. A major challenge for this class of enzymes is that the majority of procedures require an excess of the labelling reagent or, alternatively, activated substrates rather than simple commercially sourced peptides. We report the use of a coupled enzyme strategy which enables quantitative N‐ and C‐terminal labelling of proteins using unactivated labelling peptides. The use of an aminopeptidase in conjunction with a transpeptidase allows sequence‐specific degradation of the peptide by‐product, shifting the equilibrium to favor product formation, which greatly enhances the reaction efficiency. Subsequent optimisation of the reaction allows N‐terminal labelling of proteins using essentially equimolar ratios of peptide label to protein and C‐terminal labelling with only a small excess. Minimizing the amount of substrate required for quantitative labelling has the potential to improve industrial processes and facilitate the use of transpeptidation as a method for protein labelling.
A generalised coupling strategy to enable quantitative N‐ and C‐terminal labelling of proteins using unmodified peptides and readily produced catalysts is described. For C‐terminal labelling, a small excess of the labelling peptide is required, but for N‐terminal labelling, equimolar quantities of labelling reagents can be used to achieve quantitative labelling.
Light extinction by aerosols is due to scattering and absorption. The anthropogenic contribution is generally dominated by light scattering by sulfate particles and light absorption by elemental ...carbon. While real-time, in situ instrumentation for the measurement of ambient light scattering exists and is widely used (i.e., nephelometers), no such instrumentation is currently in use for the sensitive measurement of ambient light absorption by aerosols.
Instrumentation for this purpose has been developed in the past, mostly for the measurement of gaseous light absorption, but it has also been applied to the measurement of aerosol light absorption. This instrumentation is based on measuring the absorbed energy, as opposed to measuring light extinction, which is complicated by the scattering component and is also less sensitive. For aerosols, the absorbed energy heats the gas, leading to its thermal expansion. The two most sensitive techniques to detect this expansion are photoacoustic detection, in which the light source is modulated and the periodic expansion of the gas results in a sound wave at the modulation frequency, which may be detected with a microphone; and optical homodyne interferometry, in which the changed gas density is detected with a Mach-Zehnder type interferometer via the directly related change in refractive index.
This article reviews the current state of both photoacoustic and interferometric detection methods. In addition, new ideas are discussed that are currently implemented by our group and should lead to substantial improvements. Size and reliability are being improved by utilizing modern, compact solid state lasers. New designs both for the photoacoustic cell and the interferometer promise to be less susceptible to acoustic background noise. In the case of the photoacoustic cell, the new design also virtually eliminates the previously dominant noise source, coherent window noise. Furthermore, an acoustic amplifier, based on the thermoacoustic effect, is being integrated into the photoacoustic cell to further improve its sensitivity.
Aggregated particles caused by instrument artifact Pierce, Ashley M; Loría-Salazar, S. Marcela; Arnott, W. Patrick ...
Atmospheric measurement techniques,
04/2018, Letnik:
11, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Previous studies have indicated that superaggregates, clusters of aggregates of soot primary particles, can be formed in large-scale turbulent fires. Due to lower effective densities, higher ...porosity, and lower aerodynamic diameters, superaggregates may pass through inlets designed to remove particles < 2.5 µm in aerodynamic diameter (PM2.5). Ambient particulate matter samples were collected at Peavine Peak, NV, USA (2515 m) northwest of Reno, NV, USA from June to November 2014. The Teledyne Advanced Pollution Instrumentation (TAPI) 602 BetaPlus particulate monitor was used to collect PM2.5 on two filter types. During this time, aggregated particles > 2.5 µm in aerodynamic diameter were collected on 36 out of 158 sample days. On preliminary analysis, it was thought that these aggregated particles were superaggregates, depositing past PM10 (particles < 10 µm in aerodynamic diameter) pre-impactors and PM2.5 cyclones. However, further analysis revealed that these aggregated particles were dissimilar to superaggregates observed in previous studies, both in morphology and in elemental composition. To determine if the aggregated particles were superaggregates or an instrument artifact, samples were investigated for the presence of certain elements, the occurrence of fires, high relative humidity and wind speeds, as well as the use of generators on site. Samples with aggregated particles, referred to as aggregates, were analyzed using a scanning electron microscope for size and shape and energy dispersive X-ray spectroscopy was used for elemental analysis. It was determined, based on the high amounts of aluminum present in the aggregate samples, that a sampling artifact associated with the sample inlet and prolonged, high wind events was the probable reason for the observed aggregates.
Black carbon (BC), carbon monoxide (CO), and carbon dioxide (CO2) were measured in Mexico City (UNAM observatory) with a Photoacoustic Extinctiometer-PAX (BC) and a Cavity Ring-Down Spectroscopy ...analyzer-CRDS (CO and CO2), from November 2014 to July 2016. The objective of this study was to determine temporal variations of BC, CO, and CO2, their mutual correlations, and evaluation of the Mexico City emission inventory. The highest concentrations of pollutants were detected in cold dry season. The average concentrations of BC, CO, and CO2, for the entire period, were 2.95 μg m−3, 0.64 ppm, and 421.81 ppm, respectively. We calculated ΔBC/ΔCO, ΔBC/ΔCO2, and ΔCO/ΔCO2 using three methods to obtain a confidence interval for the emission ratios. BC, CO, CO2 concentrations, and the ΔBC/ΔCO ratio were maximum in the early morning, while the ΔBC/ΔCO2 and ΔCO/ΔCO2 peak was maximum in the afternoon. BC and CO have a weekday/weekend difference. The estimated slopes (ΔBC/ΔCO, ΔBC/ΔCO2, and ΔCO/ΔCO2) were compared with the emission ratios (BC/CO, BC/CO2, and CO/CO2) derived of the 2016 Mexico City emissions inventory. For mobile sources, the emission ratios of BC/CO and BC/CO2 were within the measurement range of ΔBC/ΔCO and ΔBC/ΔCO2, while CO/CO2 was underestimated in the emission inventory.
•The highest concentrations of BC, CO, and CO2 were detected in the cold dry season•BC and CO have a weekday/weekend difference•Heavy-duty vehicles (HDVs) are the dominant sources of BC in the early morning•Slopes of BC-CO-CO2 correlations provides an interval confidence for emission ratios•Evaluation of the 2016 Mexico City emission inventory
We at the Desert Research Institute (DRI*) measured volatile organic compounds (VOCs), including several mobile-source air toxics (MSATs), particulate matter with a mass mean aerodynamic diameter < ...or = 2.5 pm (PM2.5), black carbon (BC), nitrogen oxides (NOx), particulate matter (PM), and carbon monoxide (CO) on highways in Los Angeles County during summer and fall 2004, to characterize the diurnal and seasonal variations in measured concentrations related to volume and mix of traffic. Concentrations of on-road pollutants were then compared to corresponding measurements at fixed monitoring sites. The on-road concentrations of CO and MSATs were higher in the morning under stable atmospheric conditions and during periods of higher traffic volumes. In contrast, BC concentrations, measured as particulate light absorption, were higher on truck routes during the midday sampling periods despite more unstable atmospheric conditions. Compared to the measurements at the three near-road sites, the 1-hour averages of on-road BC concentrations were as much as an order of magnitude higher. The peak 1-minute average concentrations were two orders of magnitude higher for BC and were between two and six times higher for PM2.5 mass. The on-road concentrations of benzene, toluene, ethylbenzene, and xylenes (BTEX) during the summer were 3.5 +/- 0.7 and 1.2 +/- 0.6 times higher during morning and afternoon commuting periods, respectively, compared to annual average 24-hour concentrations measured at air toxic monitoring network sites. These ratios were higher during the fall, with smaller diurnal differences (4.8 +/- 0.7 and 3.9 +/- 0.6 for morning and afternoon commuting periods, respectively). Ratios similar to those for BTEX were obtained for 1,3-butadiene (BD) and styrene. On-road concentrations of formaldehyde and acetaldehyde were up to two times higher than at air toxics monitoring sites, with fall ratios slightly higher than summer ratios. Chemical mass balance (CMB) receptor model calculations attributed the sum of BTEX almost exclusively to gasoline engine exhaust for on-road samples and all but 5% to 10% of the BTEX at the three near-road sites. CMB analysis attributed 46% to 52% (+/- 7) of the ambient total particulate carbon (TC) at the three near-road sites to diesel exhaust and 10% to 17% (+/- 7) to gasoline exhaust; it attributed about 90% of the ambient elemental carbon (EC) concentrations (measured as refractory carbon using the thermal evolution method) to diesel exhaust. Diesel particulate carbon (DPC) concentrations were estimated by multiplying the mean ratio of TC to EC from the source-dominated ambient samples collected on road on Terminal Island (1.30 +/- 0.28), which is located between the Long Beach and Los Angeles ports, with the measured ambient EC concentrations at the three near-road sites. DPC estimates from EC measurements correlate well with the diesel source contributions calculated with the CMB model. The indication from these apportionments that BC or EC is a good surrogate for diesel exhaust is further supported by the positive correlation of on-road BC concentrations with volumes of truck traffic. Traffic counts have been used in past health assessment studies as surrogates for estimating near-road exposure concentrations with appropriate weighting for proximity to the road. However, the results of this study show that it is necessary to account for the proportion of diesel trucks to total vehicular traffic because of the disproportionate contribution of diesel exhaust to BC and to directly emitted PM. Alternatively, easily measured pollutants such as CO and BC can serve as reasonable surrogates for MSATs (e.g., BTEX and BD) and DPC, respectively. Measuring CO and BC is a reasonably cost-effective approach to quantifying hot-spot exposure concentrations of MSATs that is perhaps more accurate than what is possible using only data from regional air quality monitoring stations or air quality modeling results.
PDF
