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- Author or Editor: John D. Spengler x
- Journal of Applied Meteorology and Climatology x
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Abstract
This paper identifies the sources of fine and coarse inhalable particles at a site in metropolitan Boston and investigates their respective relationships to meteorological conditions. In this work, Principal Component Analysis (PCA) is applied to: 1) fine particle mass elemental data; 2) coarse particle mass elemental data, and; 3) meteorological measurements (primarily collected at nearby Logan International Airport). In addition to local surface observations, air mass trajectory information concerning each sampling day is included in the meteorological data set, allowing the consideration of air mass transport as one factor in particle impacts. As part of these PCA analyses, four different objective component selection criteria are examined and compared. The Scree test of eigenvalues is found to result in the most interpretable components for the specific air pollution and meteorological data sets considered in this work.
The rotated PCA analyses result in the identification of five fine mass particle source classes (soil, motor vehicle, coal related, oil and salt aerosols); six coarse mass particle source classes (soil, motor vehicle, refuse incineration, residual oil, salt and coarse sulfate aerosols); and five meteorological components (air mass transport over the eastern seaboard to Boston, moisture influences, poor local dispersion, season and air mass transport over the Ohio Valley/Midwest to Boston). It is found that local combustion sources (e.g., residual oil burning and motor vehicles) recorded their highest impacts during poor local dispersion and mesoscale advection from downtown Boston. Coarse soil impacts are highest at this site during dry, summertime conditions (when fugitive dust generation is at a maximum). Coal combustion-related fine particle impacts, however, are at a maximum during air mass transport into the Boston vicinity (especially from the Ohio Valley/Midwest direction), regardless of local dispersion conditions. It became obvious that meteorology plays an important role in the extent to which these particle source classes impact the monitoring site on a given day, and that it is, in large measure, the highly variable weather conditions in Boston which allow statistical approaches to discriminate the various source classes. Based on these analyses, it is concluded that both local and transported aerosols have an influence on inhalable aerosol exposures at this site, with the sulfate portion being most correlated with polluted air mass transport into the Boston area.
Abstract
This paper identifies the sources of fine and coarse inhalable particles at a site in metropolitan Boston and investigates their respective relationships to meteorological conditions. In this work, Principal Component Analysis (PCA) is applied to: 1) fine particle mass elemental data; 2) coarse particle mass elemental data, and; 3) meteorological measurements (primarily collected at nearby Logan International Airport). In addition to local surface observations, air mass trajectory information concerning each sampling day is included in the meteorological data set, allowing the consideration of air mass transport as one factor in particle impacts. As part of these PCA analyses, four different objective component selection criteria are examined and compared. The Scree test of eigenvalues is found to result in the most interpretable components for the specific air pollution and meteorological data sets considered in this work.
The rotated PCA analyses result in the identification of five fine mass particle source classes (soil, motor vehicle, coal related, oil and salt aerosols); six coarse mass particle source classes (soil, motor vehicle, refuse incineration, residual oil, salt and coarse sulfate aerosols); and five meteorological components (air mass transport over the eastern seaboard to Boston, moisture influences, poor local dispersion, season and air mass transport over the Ohio Valley/Midwest to Boston). It is found that local combustion sources (e.g., residual oil burning and motor vehicles) recorded their highest impacts during poor local dispersion and mesoscale advection from downtown Boston. Coarse soil impacts are highest at this site during dry, summertime conditions (when fugitive dust generation is at a maximum). Coal combustion-related fine particle impacts, however, are at a maximum during air mass transport into the Boston vicinity (especially from the Ohio Valley/Midwest direction), regardless of local dispersion conditions. It became obvious that meteorology plays an important role in the extent to which these particle source classes impact the monitoring site on a given day, and that it is, in large measure, the highly variable weather conditions in Boston which allow statistical approaches to discriminate the various source classes. Based on these analyses, it is concluded that both local and transported aerosols have an influence on inhalable aerosol exposures at this site, with the sulfate portion being most correlated with polluted air mass transport into the Boston area.
Abstract
The design and operation of a large vertical wind tunnel (1.8 m diameter updraft) are described, together with the associated special photographic equipment and techniques required for studies of the interactions and freezing of freely suspended water drops.
During the first two winters of operation several new and important observations have been made while freezing freely suspended, large supercooled water drops. The terminal velocity of the frozen pellet was found to be very different than that of the liquid drop. If individual drops freeze at −6C and colder they often exhibit a marked decrease (up to 4 m sec−1) in terminal velocity. Coalescence of a frozen pellet and a liquid drop produces an elongated ice pellet (8–15 mm horizontal axis) with a terminal velocity of 9 m sec−1. When an ice pellet becomes unstable and spins about a horizontal axis, it can obtain a rapid horizontal velocity. Two ice pellets frozen together display the same erratic tumbling. These observations indicate that some ice pellets have greatly increased distances and residence times to grow in the supercooled region of a cloud.
Abstract
The design and operation of a large vertical wind tunnel (1.8 m diameter updraft) are described, together with the associated special photographic equipment and techniques required for studies of the interactions and freezing of freely suspended water drops.
During the first two winters of operation several new and important observations have been made while freezing freely suspended, large supercooled water drops. The terminal velocity of the frozen pellet was found to be very different than that of the liquid drop. If individual drops freeze at −6C and colder they often exhibit a marked decrease (up to 4 m sec−1) in terminal velocity. Coalescence of a frozen pellet and a liquid drop produces an elongated ice pellet (8–15 mm horizontal axis) with a terminal velocity of 9 m sec−1. When an ice pellet becomes unstable and spins about a horizontal axis, it can obtain a rapid horizontal velocity. Two ice pellets frozen together display the same erratic tumbling. These observations indicate that some ice pellets have greatly increased distances and residence times to grow in the supercooled region of a cloud.
Abstract
Recent attempts to understand the development of intense precipitation has led several investigators to speculate about the role of drop impactions. Working with a large vertical wind tunnel, investigations were carried out on the interactions of millimeter size drops. On the basis of these studies it is concluded that drop impactions produce a rapid increase in the number of precipitation size drops (average four or five per collision) while limiting the growth of larger drops. For drops ≳4 mm in diameter there exists a spectrum of smaller drops whose relative kinetic energy of impaction exceeds the critical value of 15 ergs, thus preventing permanent coalescence. However, impactions seldom completely destroy the larger drops, but they do remove some mass. Drop impactions reveal a self-regulating mechanism in nature that enables collisions to influence both the initial growth and the determination of final size for large drops.
Abstract
Recent attempts to understand the development of intense precipitation has led several investigators to speculate about the role of drop impactions. Working with a large vertical wind tunnel, investigations were carried out on the interactions of millimeter size drops. On the basis of these studies it is concluded that drop impactions produce a rapid increase in the number of precipitation size drops (average four or five per collision) while limiting the growth of larger drops. For drops ≳4 mm in diameter there exists a spectrum of smaller drops whose relative kinetic energy of impaction exceeds the critical value of 15 ergs, thus preventing permanent coalescence. However, impactions seldom completely destroy the larger drops, but they do remove some mass. Drop impactions reveal a self-regulating mechanism in nature that enables collisions to influence both the initial growth and the determination of final size for large drops.
Abstract
Abstract
Abstract
The freezing of freely suspended, supercooled water drops by contact nucleation has been studied. Water drops were balanced in an updraft of a large vertical wind tunnel and allowed to supercool to the ambient temperature. Ice crystals introduced into the updraft were, as expected, the most effective nucleants in freezing the drops at ambient temperatures colder than and up to 0C. The results of this experiment using silver iodide and clay as contact nucleants closely agree with earlier work performed with a constant rate of cooling apparatus. The effective temperature for 100% nucleation efficiency in the case of AgI particles was −4 to −5C and for silicate particles −7 to −10C.
Abstract
The freezing of freely suspended, supercooled water drops by contact nucleation has been studied. Water drops were balanced in an updraft of a large vertical wind tunnel and allowed to supercool to the ambient temperature. Ice crystals introduced into the updraft were, as expected, the most effective nucleants in freezing the drops at ambient temperatures colder than and up to 0C. The results of this experiment using silver iodide and clay as contact nucleants closely agree with earlier work performed with a constant rate of cooling apparatus. The effective temperature for 100% nucleation efficiency in the case of AgI particles was −4 to −5C and for silicate particles −7 to −10C.
