Experimental particle formation rates spanning tropospheric sulfuric acid and ammonia abundances, ion production rates, and temperatures

Binary nucleation of sulfuric acid and water as well as ternary nucleation involving ammonia are thought to be the dominant processes responsible for new particle formation (NPF) in the cold temperatures of the middle and upper troposphere. Ions are also thought to be important for particle nucleation in these regions. However, global models presently lack experimentally measured NPF rates under controlled laboratory conditions and so at present must rely on theoretical or empirical parameterizations. Here with data obtained in the European Organization for Nuclear Research CLOUD (Cosmics Leaving OUtdoor Droplets) chamber, we present the first experimental survey of NPF rates spanning free tropospheric conditions. The conditions during nucleation cover a temperature range from 208 to 298K, sulfuric acid concentrations between 5x10(5) and 1x10(9)cm(-3), and ammonia mixing ratios from zero added ammonia, i.e., nominally pure binary, to a maximum of -1400 parts per trillion by volume (pptv). We performed nucleation studies under pure neutral conditions with zero ions being present in the chamber and at ionization rates of up to 75ion pairs cm(-3)s(-1) to study neutral and ion-induced nucleation. We found that the contribution from ion-induced nucleation is small at temperatures between 208 and 248K when ammonia is present at several pptv or higher. However, the presence of charges significantly enhances the nucleation rates, especially at 248K with zero added ammonia, and for higher temperatures independent of NH3 levels. We compare these experimental data with calculated cluster formation rates from the Atmospheric Cluster Dynamics Code with cluster evaporation rates obtained from quantum chemistry.Peer reviewe

Comparison of the SAWNUC model with CLOUD measurements of sulphuric acid-water nucleation

Binary nucleation of sulphuric acid-water particles is expected to be an important process in the free troposphere at low temperatures. SAWNUC (Sulphuric Acid Water Nucleation) is a model of binary nucleation that is based on laboratory measurements of the binding energies of sulphuric acid and water in charged and neutral clusters. Predictions of SAWNUC are compared for the first time comprehensively with experimental binary nucleation data from the CLOUD chamber at European Organization for Nuclear Research. The experimental measurements span a temperature range of 208-292K, sulphuric acid concentrations from 110(6) to 110(9)cm(-3), and distinguish between ion-induced and neutral nucleation. Good agreement, within a factor of 5, is found between the experimental and modeled formation rates for ion-induced nucleation at 278K and below and for neutral nucleation at 208 and 223K. Differences at warm temperatures are attributed to ammonia contamination which was indicated by the presence of ammonia-sulphuric acid clusters, detected by an Atmospheric Pressure Interface Time of Flight (APi-TOF) mass spectrometer. APi-TOF measurements of the sulphuric acid ion cluster distributions (H2SO4)HSO4 with i = 0, 1, ..., 10) show qualitative agreement with the SAWNUC ion cluster distributions. Remaining differences between the measured and modeled distributions are most likely due to fragmentation in the APi-TOF. The CLOUD results are in good agreement with previously measured cluster binding energies and show the SAWNUC model to be a good representation of ion-induced and neutral binary nucleation of sulphuric acid-water clusters in the middle and upper troposphere.Peer reviewe

Assessing the influence of NOx concentrations and relative humidity on secondary organic aerosol yields from alpha-pinene photo-oxidation through smog chamber experiments and modelling calculations

Secondary organic aerosol (SOA) yields from the photo-oxidation of α-pinene were investigated in smog chamber (SC) experiments at low (23–29%) and high (60–69%) relative humidity (RH), various NOx∕VOC ratios (0.04–3.8) and with different aerosol seed chemical compositions (acidic to neutralized sulfate-containing or hydrophobic organic). A combination of a scanning mobility particle sizer and an Aerodyne high-resolution time-of-flight aerosol mass spectrometer was used to determine SOA mass concentration and chemical composition. We used a Monte Carlo approach to parameterize smog chamber SOA yields as a function of the condensed phase absorptive mass, which includes the sum of OA and the corresponding bound liquid water content. High RH increased SOA yields by up to 6 times (1.5–6.4) compared to low RH. The yields at low NOx∕VOC ratios were in general higher compared to yields at high NOx∕VOC ratios. This NOx dependence follows the same trend as seen in previous studies for α-pinene SOA. A novel approach of data evaluation using volatility distributions derived from experimental data served as the basis for thermodynamic phase partitioning calculations of model mixtures in this study. These calculations predict liquid–liquid phase separation into organic-rich and electrolyte phases. At low NOx conditions, equilibrium partitioning between the gas and liquid phases can explain most of the increase in SOA yields observed at high RH, when in addition to the α-pinene photo-oxidation products described in the literature, fragmentation products are added to the model mixtures. This increase is driven by both the increase in the absorptive mass and the solution non-ideality described by the compounds' activity coefficients. In contrast, at high NOx, equilibrium partitioning alone could not explain the strong increase in the yields with RH. This suggests that other processes, e.g. reactive uptake of semi-volatile species into the liquid phase, may occur and be enhanced at higher RH, especially for compounds formed under high NOx conditions, e.g. carbonyls.ISSN:1680-7375ISSN:1680-736

Similarities in STXM-NEXAFS Spectra of Atmospheric Particles and Secondary Organic Aerosol Generated from Glyoxal, alpha-Pinene, Isoprene, 1,2,4-Trimethylbenzene, and d-Limonene

The organic functional group composition of particles produced in laboratory smog chambers were characterized by scanning transmission X-ray microscopy (STXM) with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and characteristic spectral signatures for secondary organic aerosol (SOA) were identified. The main objective of this study is to compare the single particle functional group composition of SOA formed from five precursors (glyoxal, -pinene, isoprene, 1,2,4-trimethylbenzene, and d-limonene) to the composition of ambient particles from multiple field campaigns. This has implications for understanding the potential contributions of particles similar to those produced in SOA chambers to ambient compositions during those campaigns. Glyoxal uptake studies showed absorption from mainly alkyl, carbon-nitrogen (C-N), and carboxylic carbonyl groups. The SOA formed from the photooxidation of -pinene (with and without isoprene) showed stronger absorptions for alkyl and carbonyl groups than the SOA formed from glyoxal. The mass ratio of carbonyl to acid group was larger in -pinene-only experiments relative to the mixed -pinene-isoprene experiments. Of 338 single-particle spectra available from aerosol sampling at six field campaigns, 114 particles had spectral features that were considered similar to the chamber-SOA particles: MILAGRO-2006 (9 particles), VOCALS-2008 (41 particles), Whistler-2008 (22 particles), Scripps Pier-2009 (8 particles), Bakersfield-2010 (24 particles), and Whistler-2010 (10 particles). These similarities with chamber-generated SOA provide spectroscopic evidence of chemically similar SOA products from these precursors in ambient particles. Copyright 2013 American Association for Aerosol Researc

Similarities in STXM-NEXAFS Spectra of Atmospheric Particles and Secondary Organic Aerosol Generated from Glyoxal, α-Pinene, Isoprene, 1,2,4-Trimethylbenzene, and d-Limonene

The organic functional group composition of particles produced in laboratory smog chambers were characterized by scanning transmission X-ray microscopy (STXM) with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and characteristic spectral signatures for secondary organic aerosol (SOA) were identified. The main objective of this study is to compare the single particle functional group composition of SOA formed from five precursors (glyoxal, -pinene, isoprene, 1,2,4-trimethylbenzene, and d-limonene) to the composition of ambient particles from multiple field campaigns. This has implications for understanding the potential contributions of particles similar to those produced in SOA chambers to ambient compositions during those campaigns. Glyoxal uptake studies showed absorption from mainly alkyl, carbon-nitrogen (C-N), and carboxylic carbonyl groups. The SOA formed from the photooxidation of -pinene (with and without isoprene) showed stronger absorptions for alkyl and carbonyl groups than the SOA formed from glyoxal. The mass ratio of carbonyl to acid group was larger in -pinene-only experiments relative to the mixed -pinene-isoprene experiments. Of 338 single-particle spectra available from aerosol sampling at six field campaigns, 114 particles had spectral features that were considered similar to the chamber-SOA particles: MILAGRO-2006 (9 particles), VOCALS-2008 (41 particles), Whistler-2008 (22 particles), Scripps Pier-2009 (8 particles), Bakersfield-2010 (24 particles), and Whistler-2010 (10 particles). These similarities with chamber-generated SOA provide spectroscopic evidence of chemically similar SOA products from these precursors in ambient particles. Copyright 2013 American Association for Aerosol ResearchY

Experimental particle formation rates spanning tropospheric sulfuric acid and ammonia abundances, ion production rates, and temperatures

Binary nucleation of sulfuric acid and water as well as ternary nucleation involving ammonia are thought to be the dominant processes responsible for new particle formation (NPF) in the cold temperatures of the middle and upper troposphere. Ions are also thought to be important for particle nucleation in these regions. However, global models presently lack experimentally measured NPF rates under controlled laboratory conditions and so at present must rely on theoretical or empirical parameterizations. Here with data obtained in the European Organization for Nuclear Research CLOUD (Cosmics Leaving OUtdoor Droplets) chamber, we present the first experimental survey of NPF rates spanning free tropospheric conditions. The conditions during nucleation cover a temperature range from 208 to 298 K, sulfuric acid concentrations between 5 × 105 and 1 × 109 cm−3, and ammonia mixing ratios from zero added ammonia, i.e., nominally pure binary, to a maximum of ~1400 parts per trillion by volume (pptv). We performed nucleation studies under pure neutral conditions with zero ions being present in the chamber and at ionization rates of up to 75 ion pairs cm−3 s−1 to study neutral and ion-induced nucleation. We found that the contribution from ion-induced nucleation is small at temperatures between 208 and 248 K when ammonia is present at several pptv or higher. However, the presence of charges significantly enhances the nucleation rates, especially at 248 K with zero added ammonia, and for higher temperatures independent of NH3 levels. We compare these experimental data with calculated cluster formation rates from the Atmospheric Cluster Dynamics Code with cluster evaporation rates obtained from quantum chemistry