Statistical analysis of Seoul air quality to assess the efficacy of emission abatement strategies since 1987.

The combined influences of recent mitigation measures on urban air quality have been assessed using hourly observations of the criteria air pollutants (NO, NO, O, CO, and SO) made from the Yongsan district of Seoul, Korea, over 26years (1987 to 2013). A number of data selection criteria are proposed in order to minimize variability associated with temporal changes (at diurnal, weekly, and seasonal timescales) in source strengths, their spatial distribution, and the atmospheric volume into which they mix. The temporal constraints required to better characterize relationships between observed air quality and changes in source strengths in Seoul were identified as: (i) a 5-hour diurnal sampling window (1300-1700h), (b) weekday measurements (Monday to Friday only), and (c) summer measurements (when pollutant fetch is mostly Korea-specific, and mean wind speeds are the lowest). Using these selection criteria, we were able to closely relate long-term trends identified in criteria pollutants to a number of published changes to traffic-related source strengths brought about by mitigation measures adopted over the last 10-15years.