The present paper reviews existing knowledge with regard to Organic Aerosol (OA) of importance for global climate modelling and defines critical gaps needed to reduce the involved uncertainties. All pieces required for the representation of OA in a global climate model are sketched out with special attention to Secondary Organic Aerosol (SOA): The emission estimates of primary carbonaceous particles and SOA precursor gases are summarized. The up-to-date understanding of the chemical formation and transformation of condensable organic material is outlined. Knowledge on the hygroscopicity of OA and measurements of optical properties of the organic aerosol constituents are summarized. The mechanisms of interactions of OA with clouds and dry and wet removal processes parameterisations in global models are outlined. This information is synthesized to provide a continuous analysis of the flow from the emitted material to the atmosphere up to the point of the climate impact of the produced organic aerosol. The sources of uncertainties at each step of this process are highlighted as areas that require further studies.

/pdf/organic-aerosol-and-global-climate-modelling-a-review-4ojfzx6x50.pdf

Organic aerosol and global climate modelling: a review

/pdf/aerosol-cloud-precipitation-interactions-part-1-the-nature-26b8hz0z7e.pdf

Aerosol cloud precipitation interactions. Part 1. The nature and sources of cloud-active aerosols

http://www-personal.umich.edu/~sillman/web-publications/Sillmanreview99.pdf

The relation between ozone, NOx and hydrocarbons in urban and polluted rural environments

Soils are the main sources of the greenhouse gas nitrous oxide (N2O). The N2O emission at the soil surface is the result of production and consumption processes. So far, research has concentrated on net N2O production. However, in the literature, there are numerous reports of net negative fluxes of N2O, (i.e. fluxes from the atmosphere to the soil). Such fluxes are frequent and substantial and cannot simply be dismissed as experimental noise.

Net N2O consumption has been measured under various conditions from the tropics to temperate areas, in natural and agricultural systems. Low mineral N and large moisture contents have sometimes been found to favour N2O consumption. This fits in with denitrification as the responsible process, reducing N2O to N2. However, it has also been reported that nitrifiers consume N2O in nitrifier denitrification. A contribution of various processes could explain the wide range of conditions found to allow N2O consumption, ranging from low to high temperatures, wet to dry soils, and fertilized to unfertilized plots. Generally, conditions interfering with N2O diffusion in the soil seem to enhance N2O consumption. However, the factors regulating N2O consumption are not yet well understood and merit further study.

Frequent literature reports of net N2O consumption suggest that a soil sink could help account for the current imbalance in estimated global budgets of N2O. Therefore, a systematic investigation into N2O consumption is necessary. This should concentrate on the organisms, reactions, and environmental factors involved.

Soils, a sink for N2O? A review

A European aerosol phenomenology—1: physical characteristics of particulate matter at kerbside, urban, rural and background sites in Europe

[1] A comprehensive range of aerosol parameters was measured at an urban and a rural site in the Milan, Italy metropolitan region during summer smog events in summer 1998. Measurements were performed as part of the Pianura Padana Produzione di Ozono (PIPAPO) field campaign to determine the sensitivity of O3 production to NOX and volatile organic carbon concentrations at several ground stations. Primary aerosol parameters (i.e., direct emissions) such as aerosol black carbon showed a distinct diurnal variation with maxima at about 0000 and 0800 central European summer time (CEST), in contrast to secondary aerosol parameters such as sulfate and nitrate. Aerosol number size distributions were measured under ambient conditions as well as after conditioning with volatility and hygroscopicity systems. A mode at d = 20–30 nm in the number concentration was found at 0800 CEST and exhibited high volatility at 110°C (∼80% volume lost upon heating) but no hygroscopic behavior. Based on these measurements, small particles (d < 40 nm) are thought to consist mainly of hydrophobic particulate organic matter, rather than soot or H2SO4 aerosols. Two distinct hygroscopic modes with average growth factors d/d0 ∼ 1.02 and 1.21–1.28 were found for particles with dry (relative humidity of <30%) diameters d0 = 50–200 nm. Submicrometer aerosols exhibited lower volatility at the rural than at the urban site, which is attributed to additional particulate mass produced by secondary particle formation.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2001JD001292

Urban and rural aerosol characterization of summer smog events during the PIPAPO field campaign in Milan, Italy

Measurements of concentration gradients of HNO2 and HNO3 over a semi-natural ecosystem

We present ground-based and aircraft measurements of photochemically relevant trace gases from the southern part of Switzerland from summer 1994. The region is adjacent to the Po Valley and exhibits the highest ozone concentrations within Switzerland. O3 concentrations of up to 166 parts per billion by volume (ppbv) were measured. Isoprene was 3 ppbv on the ground and 0.3 ppbv at 1000 m altitude on average in the afternoon and dominates the volatile organic compound (VOC) reactivity toward OH at the ground. Measured HONO concentrations of 0.2 ppbv in the afternoon are much higher, as can be explained from gas phase reactions alone. Radical concentrations are derived from steady state calculations using ground-based measurements in the afternoon. The resulting concentrations for OH, HO2, and RO2 are 3.1×106, 1.1×109, and 1.3×109 molecules cm−3, respectively. Isoprene and NO have the largest influence on the estimated OH concentration, followed by O3, photolysis frequency of O3, and HONO. HO2 and RO2 concentrations are most sensitive to changes in HONO, O3, and photolysis frequency of O3. The estimated radical production is larger than the NOx emissions, suggesting low-NOx chemistry. We calculated indicators for NOx or VOC sensitivity and show that reduction of NOx emissions would be more efficient in reducing O3 than VOC reduction upwind of the measurement site.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97JD00933

Photochemical oxidant formation over southern Switzerland: 1. Results from summer 1994

Concentration profiles of N2O in a grassland soil and dynamic response curves to disturbance of the soil concentration (relaxation curves) were measured with a new membrane tube technique. Diffusive properties of the soil were derived from 222Rn measurements. The mathematical analysis of the relaxation curves yielded N2O uptake rates U soil diffusivities Ds, scale lengths z*, and production rates P at different levels under the surface. The following ranges were found during 2 days of measurements: Ds = (0.4–5) × 10−7 m2 s−1, U = (1–20) × 10−4 s−1, z* = 0.7–2.8 cm, and P = 0.02–4.4 ppb s−1. These values were used to reproduce the measured N2O concentration profiles with a one-dimensional diffusive transport model of N2O in the soil air-filled pore space and to deduce flux profiles. Bidirectional fluxes occurred with small deposition fluxes up to a few ppt ms−1 during intensive growing phases of the grass. Uptake rates were high enough that N2O produced at greater depth did not reach the atmosphere.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000JD900088

A. Blatter

Papers

Urban and rural aerosol characterization of summer smog events during the PIPAPO field campaign in Milan, Italy

Measurements of concentration gradients of HNO2 and HNO3 over a semi-natural ecosystem

Photochemical oxidant formation over southern Switzerland: 1. Results from summer 1994

An experimental determination of the scale length of N2O in the soil of a grassland

NH3 soil and soil surface gas measurements in a triticale wheat field