Indoor
gases in an art museum were measured by two real-time chemical
ionization mass spectrometers (CIMS; iodide (I-CIMS) and nitrate (NO3-CIMS) reagent ions) and a proton-transfer-reaction mass spectrometer
(PTR-MS). A positive matrix factorization (PMF) analysis isolated
nine different factors capturing the variability. Three factors were
observed by all instruments, comprising over 30% of the organic carbon
from each instrument. Of these three, one factor correlated with CO2, indicating a clear influence from human occupancy, and another
was dominated by small carboxylic acids and was likely related to
building materials. The third factor was dominated by HONO and ethylene
glycol, with strong emission signatures after gallery painting. Additional
factors correlated with ozone (O3) and nitrogen dioxide
and are suggestive of indoor surface reaction products from outdoor-related
oxidants. Outdoor-related factors contributed 20% of the measured
organic carbon. Organic nitrogen compounds were measured and found
to correlate with the estimated nitrate radical (NO3) concentration.
The PTR-MS/I-CIMS/NO3-CIMS factors had higher, medium,
and lower estimated volatility, respectively, while the carbon oxidation
state followed the opposite trend. The majority of the VOC reactivity
was due to indoor-related factors (52–77%) for all oxidants
except O3 (44%). Human occupancy increased the reactivity
of the human-related (×14), small acid (×1.5), terpene (×2),
and acetone (×5) factors. The lifetime of oxidant reactivity
(τOxR) against each oxidant for all factors was greater
than the museum ventilation time scale, indicating that the reactivity
from indoor sources is largely removed outdoors. The dominant VOC
fates for all identified sources were ventilation and surface deposition.