Establishment of a structural equation model for ground-level ozone: a case study at an urban roadside site.

This study established a cause-effect relationship between ground-level ozone and latent variables employing partial least-squares analysis at an urban roadside site in four distinct seasons. Two multivariate analytic methods, factor analysis, and cluster analysis were adopted to cite and identify suitable latent variables from 14 observed variables (i.e., meteorological factors, wind and primary air pollutants) in 2008-2010. Analytical results showed that the first six components explained 80.3 % of the variance, and eigenvalues of the first four components were greater than 1. The effectiveness of this model was empirically confirmed with three indicators. Except for surface pressure, factor loadings of observed variables were 0.303-0.910 and reached statistical significance at the 5 % level. Composite reliabilities for latent variables were 0.672-0.812 and average variances were 0.404-0.547, except for latent variable "primary" in spring; thus, discriminant validity and convergent validity were marginally accepted. The developed model is suitable for the assessment of urban roadside surface ozone, considering interactions among meteorological factors, wind factors, and primary air pollutants in each season.

Interfacial transfer velocities of ozone dry deposition over agricultural soils: experimental and theoretical analysis.

A mathematical dry deposition model was developed and an experiment performed to verify that the interfacial transfer velocity (V(S)) of ozone dry deposition includes the interfacial reactive velocity (V(Sr)) and interfacial kinetic velocity (V(Sk)), as determined by measuring the ozone depletion over agricultural field soils in a dry deposition chamber. Experimental results indicate that the chemical reaction (O3 + NO --> NO2 + O2) produces the reactive velocity. Observed interfacial transfer velocities depend on nitrogen oxide emission (NO) and soil temperature (T(S)). Additionally, observed kinetic velocities of conditioned field soils increased linearly with soil temperature. Moreover, observed reactive velocities of field soils increased exponentially with soil temperature, and depend on the emission rate of nitrogen oxide. Results in this study demonstrate that interfacial transfer velocities are variable velocities for long-term transportation, that influenced factors are chemical kinetics, thermodynamics and biochemical mechanisms.

The interfacial mass transfer resistances of the ozone dry deposition over the field soil of Taichung County in Taiwan.

This study aims to design a dry deposition chamber and to measure ozone depletion over the Taichung field soil. This study seeks to verify the phenomena by an experimental and mathematical model. It is demonstrated that interfacial mass transfer resistances of ozone dry deposition involve reactive resistance (R(sr)) and kinetic resistance (R(sk)). It reveals the chemical reaction (O3 + NO --> NO2) to produce the reactive resistance, and verifies that the interfacial mass transfer resistances depend on nitrogen oxide emission and soil temperature. It shows that the interfacial mass transfer resistances are reduced with increasing soil temperature (T(S)). The model profiles are smaller than the observed data within a relative error of 15%. The reactive resistance decreases exponentially with increasing soil temperature; R(sr)(-1) (cm x sec(-1)) = 0.0001 exp (0.1455T(S)). The kinetic resistance decreases linearly with increasing soil temperature; R(sk)(-1)(cm x sec(-1)) = 0.0108T(S) + 1.4012. This model is more accurate with higher soil temperature and larger ozone concentration. Results are consistent with thermodynamics and reaction kinetics. Ozone dry deposition over agricultural soil causes conversion of nitrogen oxide (NO) to nitrogen dioxide (NO2).