With i
ncreasi
ng evide
nce of adverse health effectsassociated with particulate matter (PM), the exposureimpact of
natural sources, such as forest fires, has substa
ntialpublic health releva
nce. I
n additio
n to the threat to
nearby commu
nities, polluta
nts released from forest firesca
n travel thousa
nds of kilometers to heavily populated urba
nareas. There was a dramatic i
ncrease i
n forest fireactivity i
n the provi
nce of Quebec, Ca
nada, duri
ng July2002. The tra
nsport of PM released from these forest fireswas exami
ned usi
ng a combi
natio
n of a moderate-resolutio
n imagi
ng spectroradiometer satellite image, back-trajectories usi
ng a hybrid si
ngle-particle Lagra
ngia
ni
ntegrated trajectory, a
nd local light detectio
n a
nd ra
ngi
ngmeasureme
nts. Time- a
nd size-resolved PM was evaluatedat three ambie
nt a
nd four i
ndoor measureme
nt sitesusi
ng a combi
natio
n of direct readi
ng i
nstrume
nts (laser, time-of-flight aerosol spectrometer,
nephelometer, a
nd a
noscillati
ng microbala
nce). The tra
nsport a
nd mo
nitori
ngresults co
nsiste
ntly ide
ntified a forest fire related PM episodei
n Baltimore that occurred the first weeke
nd of July2002 a
nd resulted i
n as much as a 30-fold i
ncrease i
nambie
nt fi
ne PM. O
n the basis of tapered eleme
nt oscillati
ngmicrobala
nce measureme
nts, the 24 h PM
2.5 co
nce
ntratio
nreached 86
![](/images/e<font color=)
ntities/mgr.gif">g/m
3 o
n July 7, 2002, exceedi
ng the 24 h
natio
nal ambie
nt air quality sta
ndard. The episode wasprimarily comprised of particles less tha
n 2.5
![](/images/e<font color=)
ntities/mgr.gif">m i
naerody
namic diameter, highlighti
ng the prefere
ntial tra
nsportof the fractio
n of PM that is of greatest health co
ncer
n.Pe
netratio
n of the ambie
nt episode i
ndoors was efficie
nt(media
n i
ndoor-to-outdoor ratio 0.91) such that the highambie
nt levels were similarly experie
nced i
ndoors. Theseresults are sig
nifica
nt i
n demo
nstrati
ng the impact of a
natural source thousa
nds of kilometers away o
n ambie
ntlevels of a
nd pote
ntial exposures to air pollutio
n withi
n a
nurba
n ce
nter. This research highlights the sig
nifica
nceof tra
nsbou
ndary air pollutio
n a
nd the
need for studiesthat assess the public health impacts associated with suchsources a
nd tra
nsport processes.