Jacob Baker

Influence of Intensive Agriculture on Dry Deposition of Aerosol Nutrients

A procedure is presented for quantification of sources contributing to atmospheric aerosol chemical nutrient concentrations and dry deposition fluxes. Source apportionment using principal component analysis (PCA) and multiple linear regression analysis (MLRA) was followed by application of a size-segregated particle dry deposition model. In a rural region of southeast Brazil, biomass burning, products of secondary reactions, and soil dust re-suspension explained 43%, 31% and 21% of PM2.5 mass, respectively. Re-suspension and biomass burning contributed 22% and 19%, respectively, to PM10 mass, and re-suspension accounted for approximately half of the mass of coarse particles. At least 40% of NO3--N, 20% of phosphorus and 55% of potassium deposited originated from agriculture-related emissions. Deposition to tropical forest is currently higher than the minimum under natural conditions by factors of 12.2 (N), 6.2 (P) and 2.6 (K).

A resonance enhanced multiphoton ionization study of the CS2 molecule: The 4p Rydberg states

The resonance enhanced multiphoton ionization (REMPI) spectrum of jet‐cooled CS2 has been recorded in the one‐photon wavelength range 460–500 nm, corresponding to the three photon excitation energy range 60 000–65 000 cm−1. A previous assignment of one photon forbidden transitions in this region to 3d Rydberg states is shown to be incorrect and reassigned to the 4pπ 1,3Δu states. In fact all the observed states in this region can be assigned to 4p Rydberg states; the 4pσ 1,3Πu states at 62 768 and 62 083 cm−1, respectively, and the 4pπ 1,3Δu states at 64 214 and 63 698 cm−1, respectively. Another band at 64 374 cm−1 may be due to a three photon excitation to the 4pπ 1Σ+u Rydberg state. Our resolution is sufficient to resolve band shapes enabling symmetry assignments when coupled with their polarization behavior. The fact that the origin bands are not degraded and that Δν=0 sequence bands are strongly excited whereas Δν≠0 transitions are either absent or very weak implies that the upper states have a linea...

A two‐color (1+1′)+1 multiphoton ionization study of CS2 in the 61 000–65 600 cm−1 energy region

The (1+1′)+1 resonance enhanced multiphoton ionization (REMPI) spectrum of jet‐cooled CS2 has been recorded in the 61 000–65 600 cm−1 excitation energy range. Four prominent band groups are observed that can be assigned to Δν2=−1 and Δν2=1 sequences of the two‐photon electronically forbidden 4p 1,3Δu←X 1Σ+g transitions. Weak bands to higher energy appear to be associated with the 310, 230 and 110210 bands and corresponding sequence bands. The results show that the upper states are not 3d Rydberg states as has been previously supposed, and are consistent with a recent reinvestigation of the corresponding (3+1) REMPI spectrum. Further experimental information is obtained on the anomalous vibrational band structure of transitions to the 3Δu state. The 201 and 212 bands of the 4p 1Πu←X 1Σ+g transition are also observed, but are much weaker, suggesting that vibronic interactions are less important in this state compared to the 4p 1,3Δu states.

Photochemical trajectory modelling of ozone during the summer PUMA campaign in the UK West Midlands.

A Photochemical Trajectory Model (PTM), coupled with the Master Chemical Mechanism, is set up for summertime conditions and used to simulate pollutant levels measured in Birmingham, UK during the summer Pollution in the Urban Midlands Atmosphere (PUMA) campaign. In general, ozone is modelled well by the PTM, with reasonably good correlation and approximately 90% of afternoon and evening concentrations within a factor of two of measurements. The contribution of local biogenic emissions in the West Midlands to ozone formation during this period was also assessed and found to be of minor importance. Initially, the ozone episode of 26th June 1999, where levels of up to 87 ppb were observed was not reproduced by the UK PTM model. Sensitivity studies showed that the major cause for this was transport uncertainty in the origin and pathway of the air during conditions of slow moving anticyclonic conditions. The results indicate that the ozone episode was caused by recirculation of air polluted within the UK, with additional precursor emissions over the Netherlands, Belgium and France.