No abstract

Carboxylic acids have been detected in particles collected in various regions of the world. Here, we use experiments and Born-Oppenheimer molecular dynamics simulations to better understand the mechanism of particle formation from gas phase mixtures of formic acid (HCOOH), (CH 3) 3 N, and water vapor. A flow reaction cell coupled to two scanning mobility particle sizers has been used to measure particle size, absolute number of particles and kinetics of particle formation. Experimental results show that the addition of (CH 3) 3 N to a mixture of HCOOH and water vapor results in a dramatic increase in particle formation. Simulation results indicate that the ion-pair formation on the water surface involves direct proton transfer between HCOOH and (CH 3) 3 N. The HCOO-••(CH 3) 3 NH + ion-pair remains at the air-water interface due to hydrogen bonding and the interfacial hydration shell. This experiment-theory study shows the formation of aerosol particles from the organic acidamine interactions, which may aid in understanding the role of organics in haze and cloud droplet formation and nanoparticle growth.

Exposure to high concentrations of particulate matter has been linked to an increase in asthma, heart problems, and death. This link has increased the importance of understanding particle formation and its role in the atmosphere. Research has shown that measured particle concentrations are often higher than modeled concentrations in the atmosphere. This discrepancy is caused by unknown mechanisms that lead to particle formation. Classical nucleation theory (CNT) is one theory used to explain new particle formation. The first step in forming a particle according to CNT is agglomeration of molecules around a nucleating site. CNT has been successfully applied to modeling new particle formation using sulfuric acid and ions as nucleating sites. This article presents computational support for the use of CH3SO3H and HO2 radical as nucleating sites for new particle formation. Recent studies have shown increased particle formation rates via ions and neutral molecules with the addition of amines to the reaction mixture. We have investigated the reaction of HO2 radical with four different amines and water vapor. Our results illustrate the stabilizing effect of amines in particle formation. These results suggest that the reaction between CH3SO3H and amines as well as HO2 radical and amines in the presence of water vapor may serve as a viable mechanism for new particle formation in the atmosphere.

ABSTRACT:The results of an ab initio study on a family of hydroxy peroxy radicalwater complexes formed from the oxidation of E-2-hexenal, which constitutes an important component of biogenic atmospheric emissions, are reported. Binding energies for the b-hydroxy-c-peroxy hexanal (b-and c-positions are relative to the carbonyl) radical-water complex and the c-hydroxy-b-peroxy hexanal radical-water complex are predicted to be to 3.8 and 3.6 kcal/mol, respectively, computed at the MP2/6-311þþG(2d,2p)//B3LYP/ 6-311þþG(2d,2p) computational level. Natural bond orbital reveals that conventional hydrogen bonding between the water and the hydroxy and aldehyde functional groups of the radical are primarily responsible for the stability of the complex. It can be shown that the peroxy moiety contributes very little to the stability of the radical-water complexes. Thermochemistry calculations reveal estimated equilibrium constants that are comparable to those recently reported for several hydroxy isoprene radical-water complexes. The results of this report suggest that the hexanal peroxy radical-water complexes are expected to play a significant role in the complex chemistry of the atmosphere.

During August and September 2012, a study was conducted to determine the sources of PM2.5 adjacent to the I-710 Long Beach Freeway. The site is directly affected by the emissions from heavy diesel traffic flowing from major container ports about 10 km south of the sampling site. Hourly average data were obtained for particulate species including PM2.5, black carbon and UV absorbing carbon, EC, fine particulate nonvolatile and semi-volatile organic material (NVOM and SVOM), sulfate, nitrate, chloride, ammonium ion, and Na ion, and for related factors including O3, CO, NOX, SO2, and total traffic flow on the I-710. A total of 520 hourly averaged data sets with 15 measured variables were analyzed by EPA-PMF v5.0. The data were best described by a 10-factor solution. Based on the composition and diurnal patterns of the factors, they were assigned to three diesel-related factors (two of which appeared to represent traffic from the ports and one general freeway diesel factor), a light-duty, spark-ignition vehicle-related factor, three secondary factors (one of which was associated with O3 formation processes), and three factors dominated by sulfate, SO2, and chloride, respectively. The diurnal patterns for these last three factors are strongly correlated. Meteorological and refinery upset data indicate that they are associated with emissions from a nearby refinery. The results of the PMF analysis were combined with nephelometer light scattering, corrected for coarse particle scattering and estimated aerosol water content in a multilinear regression analysis to identify visibility degradation sources. Major contributors were the aerosol water content, and the secondary PMF factors associated with either Nitrate and NVOM or NVOM and SVOM. The use of hourly average data made possible the identification of factors associated with gasoline vehicle emissions and both port and non-port diesel emissions.Implications: Hourly averaged data were obtained for PM 2.5 , its components and factors related to primary emissions and the formation of secondary material at a near freeway sampling location adjacent to the I-710 freeway just south of the Long Beach Boulevard entrance and 10 km north of the Ports of Long Beach and Los Angeles. The major objective of the study was to determine the impact of traffic from the ports at the monitoring site. This manuscript reports on the PMF analysis of the data set. Factors related to both diesel traffic originating from the ports and diesel traffic from non-port origins were identified. The diesel traffic originating from the ports was responsible for 9% of the total traffic and 95% of the BC measured at the sampling site. The non-port diesel traffic was responsible for 15% of the total traffic and 5% of the BC. While the Port 1 diesel traffic coming from the ports contributed a large fraction of the BC, this source contributed only 2% of the CO and 5% of the NO X at the sampling site. The impact of these traffic sources on light scattering was also small. Analysis of sources of sulfate and SO ...