The Relationship Between Birch Pollen, Air Pollution and Weather Types and Their Effect on Antihistamine Purchase in Two Swedish Cities

Exposure to elevated air pollution levels can
aggravate pollen allergy symptoms. The aim of this study
was to investigate the relationships between airborne
birch (Betula) pollen, urban air pollutants NO2, O3 and
PM10 and their effects on antihistamine demand in
Gothenburg and Malmo¨, Sweden, 2006–2012. Further,
the influence of large-scale weather pattern on pollen-/
pollution-related risk, using Lambweather types (LWTs),
was analysed. Daily LWTs were obtained by comparing
the atmospheric pressure over a 16-point grid system over
southern Sweden (scale *3000 km). They include two
non-directional types, cyclonic (C) and anticyclonic
(A) and eight directional types depending on the wind
direction (N, NE, E…). Birch pollen levels were
exceptionally high under LWTs E and SE in both cities.
Furthermore, LWTs with dry and moderately calm
meteorological character (A, NE, E, SE) were associated
with strongly elevated air pollution (NO2 and PM10) in
Gothenburg. For most weather situations in both cities,
simultaneously high birch pollen together with high air
pollution had larger over-the-counter (OTC) sales of
antihistamines than situations with high birch pollen
alone. LWTs NE, E, SE and S had the highest OTC sales
in both cities. InGothenburg, the city with a higher load of
both birch pollen and air pollution, the higher OTC sales
were especially obvious and indicate an increased effect
on allergic symptoms from air pollution. Furthermore,
GothenburgLWTs A, NE, E and SEwere associatedwith
high pollen and air pollution levels and thus classified as
high-risk weather types. In Malmo¨, corresponding highrisk
LWTs were NE, E, SE and S. Furthermore,
occurrence of high pollen and air pollutants as well as
OTC sales correlated strongly with vapour pressure
deficit and temperature in Gothenburg (much less so in
Malmo¨). This provides evidence that the combination of
meteorological properties associated with LWTs can
explain high levels of birch pollen and air pollution. Our
study shows that LWTs represent a useful tool for
integrated daily air quality forecasting/warning.