− 10 7 cm −3 and the slopes of Log J vs. Log [H 2 SO 4 ] and Log J vs. Log [TMA] were 4-6 and 1, respectively, strikingly similar to the case of ammonia (NH 3 ) ternary nucleation (Benson et al., 2011). At lower RH, however, enhancement in J due to TMA was up to an order of magnitude greater than that due to NH 3 . These findings imply that both amines and NH 3 are important nucleation species, but under dry atmospheric conditions, amines may have stronger effects on H 2 SO 4 nucleation than NH 3 . Aerosol models should therefore take into account inorganic and organic base compounds together to fully understand the widespread new particle formation events in the lower troposphere.

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[1] New particle formation (NPF) occurs in various atmospheric environments, and these newly formed particles have the potential to grow to cloud condensation nuclei. But at present it is unclear which chemical species are involved in aerosol nucleation and growth, in part because there are only a limited number of simultaneous measurements of aerosol precursors and aerosol size distributions. Observations of ambient aerosol size distributions, sulfuric acid, and ammonia were made for over a year in Kent, Ohio, a relatively less polluted continental environment. Particle sizes in the diameter range from 3 to 1000 nm were measured continuously through the whole year, while sulfuric acid and ammonia were measured seasonally with two chemical ionization mass spectrometers. Strong NPF events were more frequently found during the spring and fall and less frequently during the summer and winter. The median of measured sulfuric acid was higher in spring (5.2 × 10 6 cm −3 ) and summer (2.9 × 10 6 cm −3 ) than in winter (6 × 10 5 cm −3 ) and fall (5 × 10 5 cm −3 ). We have used the inverse model Particle Growth and Nucleation to derive aerosol nucleation and growth rates from the measured aerosol size distributions. Nucleation rates derived during the NPF events ranged from 1.4 to 12.9 cm −3 s −1 and were proportional to the measured sulfuric acid concentration with a power of 0.6-2.3. Our results show that sulfuric acid is an important aerosol nucleation precursor, but only a small fraction of the aerosol growth rates could be explained by the condensation of sulfuric acid alone. Ammonia mixing ratios did not have a diurnal trend but had some seasonal variations, higher in spring than in fall and winter, typically at sub-ppbv level; aerosol nucleation rates did not show a clear correlation with ammonia at least at this sub-ppbv level, mostly because the ammonia mixing ratios were nearly constant. Our observations also indicate that the role that ammonia plays in aerosol nucleation is more complicated than is currently understood by the aerosol nucleation theories.Citation: Erupe, M. E., et al. (2010), Correlation of aerosol nucleation rate with sulfuric acid and ammonia in Kent, Ohio: An atmospheric observation,

Amines in fine particulate matter have been detected and quantified during ambient studies of winter inversions in Logan, UT, using aerosol mass spectrometry. Amine-related compounds account for 0.5-6 microg m(-3) of fine particulate mass during some wintertime periods. The amine contributions sometimes show a clear diurnal pattern, reaching peak concentrations during the middle of the nightwhile decreasing during the morning and afternoon. Smog chamber reactions show that the reaction of tertiary amines with nitrate radical can account for this behavior in the atmosphere. The lower bound reaction rate of trimethylamine and nitrate radical is estimated at 4.4 x 10(-16) cm3/molecules/s with a conversion rate to the aerosol phase of approximately 65%. This suggests that amines could be a contributor to secondary organic aerosol formation in areas where nitrate radical is a significant player in oxidation chemistry.

Abstract. Production of new particles over forests is an important source of cloud condensation nuclei that can affect climate. While such particle formation events have been widely observed, their formation mechanisms over forests are poorly understood. Our observations made in a mixed deciduous forest with large isoprene emissions during the summer displayed a surprisingly rare occurrence of new particle formation (NPF). Typically, NPF events occur around noon but no NPF events were observed during the 5 weeks of measurements. The exceptions were two evening ultrafine particle events. During the day, sulfuric acid concentrations were in the 10 6 cm −3 range with very low preexisting aerosol particles, a favorable condition for NPF to occur even during the summer. The ratio of emitted isoprene carbon to monoterpene carbon at this site was similar to that in Amazon rainforests (ratio >10), where NPF events are also very rare, compared with a ratio <0.5 in Finland boreal forests, where NPF events are frequent. Our results suggest that large isoprene emissions can suppress NPF formation in forests although the underlying mechanism for the suppression is unclear. The two evening ultrafine particle events were associated with the transported anthropogenic sulfur plumes and ultrafine particles were likely formed via ion-induced nucleation. Changes in landcover and environmental conditions could modify the isoprene suppression of NPF in some forest regions resulting in a radiative forcing that could have influence on the climate.