Diagnostic studies of the HxOy-NxOy-O3 photochemical system using data from NASA GTE field expeditions

The research effort supported in part by the subject grant focused on three related topics. Our major effort was concentrated on the analysis of data gathered during GTE field expeditions. Ancillary efforts were directed at: the development and application of a Global Chemical Transport Model for the study of the atmospheric reactive nitrogen budget; the development and application of a one-dimensional, time dependent cloud model for the study of the impact of in-cloud aqueous phase chemistry on the atmospheric sulfur budget; and mechanistic studies of the chemical processes involved in dry deposition of ozone to vegetative surfaces. In the sections below, we briefly summarize the central conclusions of each of these efforts. These discussions are followed by a listing of the papers completed during the granting period and the graduate students supported by funds from the grant. Reprints and preprints of all papers completed with support from the grant are attached as appendices

Reactive intermediates revealed in secondary organic aerosol formation from isoprene

Isoprene is a significant source of atmospheric organic aerosol; however, the oxidation pathways that lead to secondary organic aerosol (SOA) have remained elusive. Here, we identify the role of two key reactive intermediates, epoxydiols of isoprene (IEPOX = β-IEPOX + δ-IEPOX) and methacryloylperoxynitrate (MPAN), which are formed during isoprene oxidation under low- and high-NO_x conditions, respectively. Isoprene low-NO_x SOA is enhanced in the presence of acidified sulfate seed aerosol (mass yield 28.6%) over that in the presence of neutral aerosol (mass yield 1.3%). Increased uptake of IEPOX by acid-catalyzed particle-phase reactions is shown to explain this enhancement. Under high-NO_x conditions, isoprene SOA formation occurs through oxidation of its second-generation product, MPAN. The similarity of the composition of SOA formed from the photooxidation of MPAN to that formed from isoprene and methacrolein demonstrates the role of MPAN in the formation of isoprene high-NO_x SOA. Reactions of IEPOX and MPAN in the presence of anthropogenic pollutants (i.e., acidic aerosol produced from the oxidation of SO_2 and NO_2, respectively) could be a substantial source of “missing urban SOA” not included in current atmospheric models

Regional simulation of anthropogenic sulfur over East Asia and its sensitivity to model parameters

We discuss a series of simulations of anthropogenic sulfur over East Asia with a SO 2 /SO 4 2− chemistry-transport model driven in on-line mode by a regional climate model. Sensitivity to OH and H 2 O 2 concentration, cloud parameters, SO 2 dry deposition and emission strength is analyzed and the different components of the sulfur budget are examined. The SO 2 and SO 2− 4 column burdens show pronounced variability at temporal scales from seasonal to synoptic and sub-daily, with SO 2 and SO 2− 4 behaving differently due to the interplay of chemical conversion, removal and transport processes. Both SO 2 and SO 2− 4 show marked spatial variability, with emission being the dominant term in regulating the SO 2 spatial distribution. The atmospheric SO 2 and SO 2− 4 amounts show close to a linear response to surface emission. Aqueous phase SO 2 →SO 2− 4 conversion and wet removal are the primary factors that regulate the SO 2− 4 amounts, with dry deposition and gas phase SO 2 →SO 2− 4 conversion being of secondary importance. Aqueous phase conversion and dry deposition are the dominant loss mechanisms for SO 2 . The model shows low sensitivity to variations in OH, H 2 O 2 , and cloud parameters, while the sensitivity to prescribed dry deposition velocity is more pronounced. Overall, our results are in line with previous modeling studies and with very limited available observations. DOI: 10.1034/j.1600-0889.2001.d01-14.

Aerosol radiative, physical, and chemical properties in Beijing during June 1999

Beijing experiences air pollution such that the sky overhead is gray much of the time even on cloudless days. In order to understand the cause of this problem, the aerosol light scattering coefficient σ_(sp) and absorption coefficient σ_(ap) were measured under dry conditions (instrumental relative humidity 1.0 μm), the submicron aerosol was responsible for ∼80% of the light scattering at 530 nm. The largest contribution to the PM2.5 aerosol mass was due to organic compounds, which accounted for ∼30% of the mass. The contributions of sulfate, ammonium, and nitrate to the PM2.5 mass concentration were ∼15%, 5%, and 8%, respectively. Mineral aerosol contributed ∼16% to the PM2.5 aerosol mass. These data show that combustion-related particles rather than wind-blown dust dominated the light extinction budget during June 1999

Rates of fixation by lightning of carbon and nitrogen in possible primitive atmospheres

A thermochemical-hydrodynamic model of the production of trace species by electrical discharges has been used to estimate the rates of fixation of C and N by lightning in the primitive atmosphere. Calculations for various possible mixtures of CH 4 , CO 2 , N 2 , H 2 , and H 2 O reveal that the prime species produced were probably HCN and NO and that the key parameter determining the rates of fixation was the ratio of C atoms to O atoms in the atmosphere. Atmospheres with C more abundant than O have large HCN fixation rates, in excess of 10 17 molecules J −1 , but small NO yields. However, when O is more abundant than C, the NO fixation rate approaches 10 17 molecules J −1 while the HCN yield is small. The implications for the evolution of life are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43346/1/11084_2004_Article_BF00931483.pd

Origin of Ozone NO(x) in the Tropical Troposphere: A Photochemical Analysis of Aircraft Observations Over the South Atlantic Basin

The photochemistry of the troposphere over the South Atlantic basin is examined by modeling of aircraft observations up to 12-km altitude taken during the TRACE A expedition in September-October 1992. A close balance is found in the 0 to 12-km column between photochemical production and loss Of O3, with net production at high altitudes compensating for weak net loss at low altitudes. This balance implies that O3 concentrations in the 0-12 km column can be explained solely by in situ photochemistry; influx from the stratosphere is negligible. Simulation of H2O2, CH3OOH, and CH2O concentrations measured aboard the aircraft lends confidence in the computations of O3 production and loss rates, although there appears to be a major gap in current understanding of CH2O chemistry in the marine boundary layer. The primary sources of NO(x) over the South Atlantic Basin appear to be continental (biomass burning, lightning, soils). There is evidence that NO(x) throughout the 0 to 12-km column is recycled from its oxidation products rather than directly transported from its primary sources. There is also evidence for rapid conversion of HNO3 to NO(x) in the upper troposphere by a mechanism not included in current models. A general representation of the O3 budget in the tropical troposphere is proposed that couples the large scale Walker circulation and in situ photochemistry. Deep convection in the rising branches of the Walker circulation injects NO(x) from combustion, soils, and lightning to the upper troposphere, leading to O3 production; eventually, the air subsides and net O3 loss takes place in the lower troposphere, closing the O3 cycle. This scheme implies a great sensitivity of the oxidizing power of the atmosphere to NO(x) emissions in the tropics

Formaldehyde, glyoxal, and methylglyoxal in air and cloudwater at a rural mountain site in central Virginia

As part of the Shenandoah Cloud and Photochemistry Experiment (SCAPE), we measured formaldehyde (HCHO), glyoxal (CHOCHO), and methylglyoxal (CH3C(O)CHO) concentrations in air and cloudwater at Pinnacles (elevation 1037 m) in Shenandoah National Park during September 1990. Mean gas‐phase concentrations of HCHO and CHOCHO were 980 and 44 pptv, respectively. The concentration of CH3C(O)CHO rarely exceeded the detection limit of 50 pptv. Mean cloudwater concentrations of HCHO and CHOCHO were 9 and 2 μM, respectively; the mean CH3C(O)CHO concentration was below its detection limit of 0.3 μM. The maximum carbonyl concentrations were observed during stagnation events with high O3, peroxides, and CO. Outside of these events the carbonyls did not correlate significantly with O3, CO, or NOy. Carbonyl concentrations and concentration ratios were consistent with a major source for the carbonyls from isoprene oxidation. Oxidation of CH4 supplies a significant background of HCHO. The carbonyl concentrations were indistinguishable in two size fractions of cloudwater having a cut at d=18 μm. Gas‐ and aqueous‐phase concentrations of HCHO from samples collected during a nighttime cloud event agree with thermodynamic equilibria within a factor of 2. Samples collected during a daytime cloud event show HCHO supersaturation by up to a factor of 4. Positive artifacts in the cloudwater samples due to hydrolysis of hydroxymethylhydroperoxide (HOCH2OOH) could perhaps account for this discrepancy

A change in the transportation needs today, a better future for tomorrow – climate change review

No sooner than later, the world will be living hell as a result of the transportation effects on our climate now escalating. The pressure is now growing towards their resultant effects to be totally eradicated in order to save our planet otherwise, the stabilisation of these effects; global warming, greenhouse gas (GHG) emission and degradation will need to be sought after. The world all over is at it now in an effort to restore our climate, to save it from the effects of these catastrophes/disasters. On the proposition of the Kyoto Protocol in1997, the main focus was to decrease greenhouse emissions of mainly six gases – Carbon dioxide, methane, nitrous oxide, sulphur hexafluoride, Hydro fluorocarbons (HFCs) and Per fluorinated Compounds (PFCs). And transport alone, accounts for over 26% of global CO2 and has been regarded as one of the few industrial sectors wherein emissions are still on the increase, on this basis, researchers and policy makers are all at it to tackle the menace of climate changes through provision of sustainable transport. This paper focuses on the new and developed technologies like the renewable energy source [RES], which will be an alternative to transport fuels to avoid the dependence on petroleum which after effects are damaging to the world climate, and may probably not be there forever to continue serving the world ever increasing population. While the long term solutions are being sought, these alternatives will make do for now