Stability of Spatial Distribution Patterns of NO₂ Concentration

Statistical Analysis of the Survey by a Dense Network of Measurements with Diffusion Samplers

Abstract

In order to evaluate temporal variation of spatial distribution patterns of NO₂ concentration, daily average concentration was measured by diffusion samplers at every 1 km2 mesh in an area of about 30 km² in the suburbs of Tokyo. Survey was carried out over 7 days each in April and in December of 1984. Analysis of variance of a 2 way classification, whose criteria are days and sampling points, shows;
(1) Variance between days (D) is extremely large. Spatial averages vary markedly day by day, reflecting human activities and meteorological conditions, especially wind speed.
(2) Variance between sampling points (P) is large in comparison with variance due to P×D interaction terms. Features of spatial distribution pattern that NO₂ concentration is high around the crossings of principal roads are common to all days.
(3) Spatial distribution pattern varies somewhat according to the prevailing wind direction of the day. Variance within group is reduced to the same order of magnitude as variance of measurement error when variance due to P×D interaction is partitioned by wind directions.