Atmospheric transformation of monoterpenes gives products that may cause environmental consequences. In this work the NO 3 radical-initiated oxidation of the monoterpenes R-pinene, -pinene, ∆ 3 -carene, and limonene has been investigated. All experiments were conducted in EUPHORE, the EUropean PHOto REactor facility in Valencia, Spain. The aerosol and product yields were measured in experiments with a conversion of the terpenes in the interval from 7 to 400 ppb. The lower end of the concentrations used are close to those measured in ambient pine forest air. Products were measured using long path in situ FTIR. Aerosol yields were obtained using a DMA-CPC system. The aerosol mass yields measured at low concentrations (10 ppb terpene reacted) were <1, 10, 15, and 17% for R-pinene, -pinene, ∆ 3 -carene, and limonene, respectively. The total molar alkylnitrate yields were calculated to be 19, 61, 66, and 48%, and molar carbonyl compound yields were estimated to be 71, 14, 29, and 69% for R-pinene, -pinene, ∆ 3 -carene, and limonene, respectively. The aerosol yields were strongly dependent on the amounts of terpene reacted, whereas the nitrate and carbonyl yields do not depend on the amount of terpene converted. The principal carbonyl compound from R-pinene oxidation was pinonaldehyde. In the case of limonene, endolim was tentatively identified and appears to be a major product. The reactions with -pinene and ∆ 3 -carene yielded 1-2% of nopinone and 2-3% caronaldehyde, respectively. The results show that it is not possible to use generalized descriptions of terpene chemistry, e.g. in matematical models.

Anthropogenic mercury emissions are transported through the atmosphere as gaseous elemental mercury (Hg(0)) prior to deposition to Earth's surface. Strong seasonality in atmospheric Hg(0) concentrations in the Northern Hemisphere has been explained by two factors: anthropogenic Hg(0) emissions are thought to peak in winter due to higher energy consumption, and atmospheric oxidation rates of Hg(0) are faster in summer. Oxidationdriven Hg(0) seasonality should be equally pronounced in the Southern Hemisphere, which is inconsistent with observations of constant year-round Hg(0) levels. Here, we assess the role of Hg(0) uptake by vegetation as an alternative mechanism for driving Hg(0) seasonality. We find that at terrestrial sites in the Northern Hemisphere, Hg(0) co-varies with CO2, which is

The reaction between NO 3 and R-pinene has been studied in large reaction chambers of 0.5-200 m 3 volume, using long path FT-IR, GC-ECD, and GC-FID for the analyses. The reaction yielded 62 ( 4% pinonaldehyde (3-acetyl-2,2dimethylcyclobutane acetaldehyde) and 3 ( 0.5% pinane epoxide. The total yield of alkylnitrates was estimated to be approximately 14%; two of the nitrates have been identified as 3-oxypinane-2-nitrate, and 2-hydroxy-3nitrate with yields of 3 ( 0.2% and 5 ( 0.4%, respectively. This work represents the first quantitative identification of pinonaldehyde and alkylnitrates from the reaction of NO 3 with R-pinene. A thermally stable peroxy acylnitrate was observed to be formed from secondary reactions of pinonaldehyde in the system. This compound has been assigned to 3-acetyl-2,2-dimethylcyclobutane acetylperoxynitrate. Possible implications for the atmospheric NO x chemistry are discussed. From the product data, a mechanism for the NO 3 + R-pinene reaction has been constructed.

Large yields of dicarbonyl compounds have been found in the atmospheric oxidation of R-pinene and ∆ 3 -carene. These terpenes are emitted in large quantities by biogenic sources, and it is important to know the fate of their reaction products. In this investigation, ultraviolet and infrared absorption cross sections, vapor pressures, and rate coefficients for hydroxyl and nitrate radical reactions have been determined for the main product in each case, i.e., 3-acetyl-2,2-dimethylcyclobutaneacetaldehyde (pinonaldehyde) and 2,2-dimethyl-3-(2-oxopropyl)cyclopropaneacetaldehyde (caronaldehyde). Photolysis lifetimes at noon on July 1 at 50°N using a photolysis quantum yield of 1 are 3.3 h for pinonaldehyde and 5.8 h for caronaldehyde. The infrared absorption cross sections obtained (base e) were (8.08 ( 0.32) × 10 -19 and (1.04 ( 0.05) × 10 -18 cm 2 molecule -1 for pinonaldehyde and caronaldehyde at 1725.4 and 1741.5 cm -1 , respectively. Vapour pressures determined by Knudsen effusion measurements are 5.1 and 3.0 Pa at 298 K. The rate coefficients obtained using the relative rate technique for reaction with OH radicals were (8.72 ( 1.14) × 10 -11 and (1.21 ( 0.36) × 10 -10 molecules cm -3 s -1 for pinonaldehyde and caronaldehyde and for the corresponding NO 3 reactions were (2.35 ( 0.37) × 10 -14 and (2.71 ( 0.15) × 10 -14 molecules cm -3 s -1 . The vapor pressures are too high for homogenous nucleation or direct condensation to take place in the atmosphere. The dominant gas-phase removal processes will be reaction with OH radicals and possibly also photodissociation.

Long-term monitoring of data of ambient mercury (Hg) on a global scale to assess its emission, transport, atmospheric chemistry, and deposition processes is vital to understanding the impact of Hg pollution on the environment. The Global Mercury Observation System (GMOS) project was funded by the European Commission (http://www.gmos.eu) and started in November 2010 with the overall goal to develop a coordinated global observing system to monitor Hg on a global scale, including a large network of ground-based monitoring stations, ad hoc periodic oceanographic cruises and measurement flights in the lower and upper troposphere as well as in the lower stratosphere. To date, more than 40 ground-based monitoring sites constitute the global network covering many regions where little to no observational data were available before GMOS. This work presents atmospheric Hg concentrations recorded worldwide in the framework of the GMOS project (2010-2015), analyzing Hg measurement results in terms of temporal trends, seasonality and comparability within the network. Major findings highlighted in this paper include a clear gradient of Hg concentrations between the Northern and Southern hemispheres, confirming that the gradient observed is mostly driven by local and regional sources, which can be anthropogenic, natural or a combination of both.