Aerosols in the Pre-industrial Atmosphere

Purpose of Review: We assess the current understanding of the state and behaviour of aerosols under pre-industrial conditions and the importance for climate. Recent Findings: Studies show that the magnitude of anthropogenic aerosol radiative forcing over the industrial period calculated by climate models is strongly affected by the abundance and properties of aerosols in the pre-industrial atmosphere. The low concentration of aerosol particles under relatively pristine conditions means that global mean cloud albedo may have been twice as sensitive to changes in natural aerosol emissions under pre-industrial conditions compared to present-day conditions. Consequently, the discovery of new aerosol formation processes and revisions to aerosol emissions have large effects on simulated historical aerosol radiative forcing. Summary: We review what is known about the microphysical, chemical, and radiative properties of aerosols in the pre-industrial atmosphere and the processes that control them. Aerosol properties were controlled by a combination of natural emissions, modification of the natural emissions by human activities such as land-use change, and anthropogenic emissions from biofuel combustion and early industrial processes. Although aerosol concentrations were lower in the pre-industrial atmosphere than today, model simulations show that relatively high aerosol concentrations could have been maintained over continental regions due to biogenically controlled new particle formation and wildfires. Despite the importance of pre-industrial aerosols for historical climate change, the relevant processes and emissions are given relatively little consideration in climate models, and there have been very few attempts to evaluate them. Consequently, we have very low confidence in the ability of models to simulate the aerosol conditions that form the baseline for historical climate simulations. Nevertheless, it is clear that the 1850s should be regarded as an early industrial reference period, and the aerosol forcing calculated from this period is smaller than the forcing since 1750. Improvements in historical reconstructions of natural and early anthropogenic emissions, exploitation of new Earth system models, and a deeper understanding and evaluation of the controlling processes are key aspects to reducing uncertainties in future

Estimation of local and external contributions of biomass burning to PM2.5 in an industrial zone included in a large urban settlement

A total of 85 PM2.5 samples were collected at a site located in a large industrial zone (Porto Marghera, Venice, Italy) during a 1-year-long sampling campaign. Samples were analyzed to determine water-soluble inorganic ions, elemental and organic carbon, and levoglucosan, and results were processed to investigate the seasonal patterns, the relationship between the analyzed species, and the most probable sources by using a set of tools, including (i) conditional probability function (CPF), (ii) conditional bivariate probability function (CBPF), (iii) concentration weighted trajectory (CWT), and (iv) potential source contribution function (PSCF) analyses. Furthermore, the importance of biomass combustions to PM2.5 was also estimated. Average PM2.5 concentrations ranged between 54 and 16 μg m−3 in the cold and warm period, respectively. The mean value of total ions was 11 μg m−3 (range 1–46 μg m−3): The most abundant ion was nitrate with a share of 44 % followed by sulfate (29 %), ammonium (14 %), potassium (4 %), and chloride (4 %). Levoglucosan accounted for 1.2 % of the PM2.5 mass, and its concentration ranged from few ng m−3 in warm periods to 2.66 μg m−3 during winter. Average concentrations of levoglucosan during the cold period were higher than those found in other European urban sites. This result may indicate a great influence of biomass combustions on particulate matter pollution. Elemental and organic carbon (EC, OC) showed similar behavior, with the highest contributions during cold periods and lower during summer. The ratios between biomass burning indicators (K+, Cl−, NO3−, SO42−, levoglucosan, EC, and OC) were used as proxy for the biomass burning estimation, and the contribution to the OC and PM2.5 was also calculated by using the levoglucosan (LG)/OC and LG/PM2.5 ratios and was estimated to be 29 and 18 %, respectively

Emission factors of hydrocarbons, halocarbons, trace gases and particles from biomass burning in Brazil

Airborne measurements of the emissions of gases and particles from 19 individual forest, cerrado, and pasture fires in Brazil were obtained during the Smoke, Clouds, and Radiation-Brazil (SCAR-B) study in August-September 1995. Emission factors were determined for a number of major and minor gaseous and particulate species, including carbon dioxide, carbon monoxide, sulfur dioxide, nitrogen oxides, methane, nonmethane hydrocarbons, halocarbons, particulate (black and organic) carbon, and particulate ionic species. The magnitude of the emission factors for gaseous species were determined primarily by the relative amounts of flaming and smoldering combustion, rather than differences in vegetation type. Hydrocarbons and halocarbons were well correlated with CO, which is indicative of emissions primarily associated with smoldering combustion. Although there was large variability between fires, higher emission factors for SO2 and NOx were associated with an increased ratio of flaming to smoldering combustion; this could be due to variations in the amounts of sulfur and nitrogen in the fuels. Emission factors for particles were not so clearly associated with smoldering combustion as those for hydrocarbons. The emission factors measured in this study are similar to those measured previously in Brazil and Africa. However, particle emission factors from fires in Brazil appear to be roughly 20 to 40% lower than those from North American boreal forest fires. Copyright 1998 by the American Geophysical Union

Modelling the multiphase near-surface chemistry related to ozone depletions in polar spring

Near-total depletions of ozone have been observed in the Arctic spring since the mid1980s. The autocatalytic reaction cycles involving reactive halogens are now recognized to be of main importance for ozone depletion events in the polar boundary layer. We present sensitivity studies using the model MISTRA in the boxmodelmode on the influence of chemical species on these ozone depletion processes. In order to test the sensitivity of the chemistry under polar conditions, we compared base runs undergoing fluxes of either Br2,BrCl, or Cl2 to induce ozone depletions, with similar runs including a modification of thechemical conditions. The role of HCHO, H2O2, DMS, Cl2, C2H6, HONO, NO2, and RONO2 was investigated. Cases with elevated mixing ratios of HCHO, H2O2, DMS, Cl2, and HONO induceda shift in bromine speciation from Br/BrO to HOBr/HBr, while high mixing ratios of C2H6 induced a shift from HOBr/HBr to Br/BrO. The shifts from Br/BrO to HOBr/HBr accelerated the aerosol debromination, but also increased the total amount of deposited bromine at thesurface (mainly via increased deposition of HOBr). For all NOy species studied (HONO, NO2, RONO2) the chemistry is characterized by an increased bromine deposition on snow reducing the amount of reactive bromine in the air. Ozone is less depleted under conditions of high mixing ratios of NOx. The production of HNO3 led to the acid displacement of HCl, and the release of chlorine out of salt aerosol (Cl2 or BrCl) increased