Progress in urban climatology over the two decades since the first publication of the International Journal of Climatology is reviewed. It is emphasized that urban climatology during this period has benefited from conceptual advances made in microclimatology and boundary-layer climatology in general. The role of scale, heterogeneity, dynamic source areas for turbulent fluxes and the complexity introduced by the roughness sublayer over the tall, rigid roughness elements of cities is described. The diversity of urban heat islands, depending on the medium sensed and the sensing technique, is explained. The review focuses on two areas within urban climatology. First, it assesses advances in the study of selected urban climatic processes relating to urban atmospheric turbulence (including surface roughness) and exchange processes for energy and water, at scales of consideration ranging from individual facets of the urban environment, through streets and city blocks to neighbourhoods. Second, it explores the literature on the urban temperature field. The state of knowledge about urban heat islands around 1980 is described and work since then is assessed in terms of similarities to and contrasts with that situation. Finally, the main advances are summarized and recommendations for urban climate work in the future are made. Copyright © 2003 Royal Meteorological Society.

/pdf/two-decades-of-urban-climate-research-a-review-of-turbulence-12p43b6trj.pdf

Two decades of urban climate research: a review of turbulence, exchanges of energy and water, and the urban heat island

The use of fire as a tool to manipulate the environment has been instrumental in the human conquest of Earth, the first evidence of the use of fires by early hominids dating back to 1–1.5 million years ago [1]. Even today, most human-ignited vegetation fires take place on the African continent, and its widespread, frequently burned savannas bear ample witness to this. Although natural fires can occur even in tropical forest regions [2, 3], the extent of fires has greatly expanded on all continents with the arrival of Homo sapiens. Measurements of charcoal in dated sediment cores have shown clear correlations between the rate of burning and human settlement [4]. Pollen records show a shift with human settlement from pyrophobic vegetation to pyrotolerant and pyrophilic species, testimony to the large ecological impact of human-induced fires.

https://science.sciencemag.org/content/sci/250/4988/1669.full.pdf

Biomass Burning in the Tropics: Impact on Atmospheric Chemistry and Biogeochemical Cycles

Formation and growth rates of ultrafine atmospheric particles: a review of observations

Sources, Effects and Risks of Ionizing Radiation

Six change detection procedures were tested using Landsat MultiSpectral Scanner (MSS) images for detecting areas of changes in the region of the Terminos Lagoon, a coastal zone of the State of Campeche, Mexico. The change detection techniques considered were image differencing, vegetative index differencing, selective principal components analysis (SPCA), direct multi-date unsupervised classification, post-classification change differencing and a combination of image enhancement and post-classification comparison. The accuracy of the results obtained by each technique was evaluated by comparison with aerial photographs through Kappa coefficient calculation. Post-classification comparison was found to be the most accurate procedure and presented the advantage of indicating the nature of the changes. Poor performances obtained by image enhancement procedures were attributed to the spectral variation due to differences in soil moisture and in vegetation phenology between both scenes. Methods based on classif...

Monitoring land-cover changes: A comparison of change detection techniques

Results of ozone and Aitken condensation nuclei measurements made over the rain forest in equatorial Africa during February 12-25, 1988 are presented. The results indicate the presence of a layer between 1 and 4 km altitude where these species are strongly enriched. Based on information derived from simultaneous measurements of other chemical and meteorological parameters, satellite imagery, and trajectory calculations, this enrichment is attributed to emissions from biomass burning in sub-Saharan Africa, from which ozone is formed by photochemical reactions.

Ozone and Aitken nuclei over equatorial Africa: Airborne observations during DECAFE 88

Surface ozone measurements obtained at Brazzaville, Congo (4°20′S, 15°20′E), from 1983 to 1986 are summarized. In addition, results from aircraft surveys (1985 and 1986) from Brazzaville to the Atlantic coast and results from a shipboard expedition (1986) along the Atlantic coast at the Equator are presented. On the basis of the data, there appears to exist a seasonal cycle with the highest values in early spring (southern) which compare with the mid-latitude values observed in the northern hemisphere. The data suggest that during the dry season, emission of precursor gases from biomass burning leads to high ozone values in the boundary layer. Ozone mixing ratios approached levels as high as 100 parts per billion by volume in a layer residing just above the monsoon. In the wet season, the data suggest that biogenic, organic emissions may act as precursors to photochemical ozone production and may contribute to the fairly high ozone burden of the lower troposphere over Equatorial Africa.

Seasonal trends of ozone in equatorial Africa: Experimental evidence of photochemical formation

Comparison between weekend and weekday ozone concentration in large cities in France

An experiment was conducted in a pine forest in southwestern France during late spring 1992. The aim was fourfold: testing various flux measurement methodologies for chemically reactive species; quantifying the exchanges between the forest and the atmosphere; analyzing the involved mechanisms; and studying their influence on the chemistry of the surface boundary layer. This paper presents preliminary results obtained on the dry deposition of ozone and submicronic aerosol particles, measured using eddy correlation. Once properly normalized, the spectra and cospectra of all scalar species exhibit universal shapes over the whole frequency range. However, evidence is provided that under some meteorological conditions the time series of turbulent variables can be affected by nonstationary trends, or low-frequency fluctuations that do not contribute to vertical transfer but whose presence can induce large errors in the calculated fluxes. The time variations of the deposition velocities for ozone and aerosol particles are then presented over 2 days with different meteorological conditions. The deposition velocities are shown to be consistent with other reported studies. Dry deposition of ozone appears to be mainly governed by the stomatal resistance, whereas friction velocity and atmospheric instability in the boundary layer seem to govern the deposition of aerosol particles.

Jacques Fontan

Papers

Ozone and Aitken nuclei over equatorial Africa: Airborne observations during DECAFE 88

Seasonal trends of ozone in equatorial Africa: Experimental evidence of photochemical formation

Comparison between weekend and weekday ozone concentration in large cities in France

The Landes experiment: Biosphere‐atmosphere exchanges of ozone and aerosol particles above a pine forest

Evolution times of tropospheric negative ions