The development o
f a new high-resolution time-o
f-
flightaerosol mass spectrometer (HR-ToF-AMS) is reported.The high-resolution capabilities o
f this instrument allowthe direct separation o
f most ions
from inorganic andorganic species at the same nominal
m/
z, the quanti
fication o
f several types o
f organic
fragments (C
xH
y, C
xH
yO
z,C
xH
yN
p, C
xH
yO
zN
p), and the direct identi
fication o
f organicnitrogen and organosul
fur content. This real-time instrument is
field-deployable, and its high time resolution (0.5Hz has been demonstrated) makes it well-suited
forstudies in which time resolution is critical, such as aircra
ftstudies. The instrument has two ion optical modes: asingle-re
flection con
figuration o
ffers higher sensitivity andlower resolving power (up to ~2100 at
m/
z 200), and atwo-re
flectron con
figuration yields higher resolving power(up to ~4300 at
m/
z 200) with lower sensitivity. Theinstrument also allows the determination o
f the sizedistributions o
f all ions. One-minute detection limits
forsubmicrometer aerosol are <0.04
f">g m
-3 for all speciesin the high-sensitivity mode and <0.4
f">g m
-3 in the high-resolution mode. Examples o
f ambient aerosol data arepresented
from the SOAR-1 study in Riverside, CA, inwhich the spectra o
f ambient organic species are dominated by C
xH
y and C
xH
yO
z fragments, and di
fferentorganic and inorganic
fragments at the same nominal
m/
zshow di
fferent size distributions. Data are also presented
from the MIRAGE C-130 aircra
ft study near Mexico City,showing high correlation with independent measurementso
f surrogate aerosol mass concentration.