Abstract:
Air pollution is a severe problem in Almaty (Kazakhstan), especially during the cold half of the
year (October-March). Almaty is one of the most polluted cities in Kazakhstan and Central Asia,
with average winter PM2.5 (particulate matter with aerodynamic diameter ≤ 2.5 µm) concentration
of 94.0 µg m–3
. High pollution in the wintertime in Almaty could be caused by emissions from coal
combustion for power and heat generation (at power plants and small-scale heating), which
could also be worsened by poor dispersion of air pollutants due to certain atmospheric conditions.
Based on one-year radiosonde data, the characteristics of the planetary boundary layer height
(PBLH) and its effect on ground-level PM2.5 concentrations in Almaty were analyzed in this study
using the bulk Richardson number (Ri) and potential temperature increase (PT) methods. During
an annual cycle, the concentrations of PM2.5 were highest in the winter months when the daily
concentrations were above 100 µg m–3 for 38 days during this period. The results show a clear
negative relationship between the daily average PM2.5 concentrations and PBLH at 12.00 UTС. For
instance, high PM2.5 concentrations in winter months (94.0 µg m–3
) corresponded to a lower PBLH
(393 m), and low PM2.5 concentrations in summer months (9.9 µg m–3
) corresponded to a higher
PBLH (1970 m). During the cold half of the year, the top 20% of PM2.5 concentrations were
associated with a lower PBLH and calm wind conditions (lower average wind speeds within the
PBL and a lower ventilation coefficient). The results show that PBLH variations during the year
have a significant effect on PM2.5 concentrations; however, further analysis is needed with a more
substantial amount of observational data to understand this interaction further and to investigate
the role of synoptic processes that lead to a shallow PBLH.