Ben Liley

Impacts of biomass burning in Southeast Asia on ozone and reactive nitrogen over the western Pacific in spring

[1] Aircraft measurements of ozone (O3) and its precursors (reactive nitrogen, CO, nonmethane hydrocarbons) were made over the western Pacific during the Transport and Chemical Evolution Over the Pacific (TRACE-P) campaign, which was conducted during February–April 2001. Biomass burning activity was high over Southeast Asia (SEA) during this period (dry season), and convective activity over SEA frequently transported air from the boundary layer to the free troposphere, followed by eastward transport to the sampling region over the western Pacific south of 30� N. This data set allows for systematic investigations of the chemical and physical processes in the outflow from SEA. Methyl chloride (CH3Cl) and CO are chosen as primary and secondary tracers, respectively, to gauge the degree of the impact of emissions of trace species from biomass burning. Biomass burning is found to be a major source of reactive nitrogen (NOx, PAN, HNO3, and nitrate) and O3 in this region from correlations of these species with the tracers. Changes in the abundance of reactive nitrogen during upward transport are quantified from the altitude change of the slopes of the correlations of these species with CO. NOx decreased with altitude due to its oxidation to HNO3. On the other hand, PAN was conserved during transport from the lower to the middle troposphere, consistent with its low water solubility and chemical stability at low temperatures. Large losses of HNO3 and nitrate, which are highly water soluble, occurred in the free troposphere, most likely due to wet removal by precipitation. This has been shown to be the major pathway of NOy loss in the middle troposphere. Increases in the mixing ratios of O3 and its precursors due to biomass burning in SEA are estimated using the tracers. Enhancements of CO and total reactive nitrogen (NOy), which are directly emitted from biomass burning, were largest at 2–4 km. At this altitudetheincreasesinNOyandO3were810partspertrillionbyvolume(pptv)and26parts per billion by volume (ppbv) above their background values of 240 pptv and 31 ppbv, respectively. The slope of the O3-CO correlation in biomass burning plumes was similar to those observed in fire plumes in northern Australia, Africa, and Canada. The O3 production efficiency (OPE) derived from the O3-CO slope and NOx/CO emission ratio (ER) is shown to be positively correlated with the C2H4/NOx ER, indicating that the C2H4/NOx ER is a critical parameter in determining the OPE. Comparison of the net O3 flux across the western Pacific region and total O3 production due to biomass burning in

Serum 25-hydroxyvitamin-D responses to multiple UV exposures from solaria: inferences for exposure to sunlight.

We investigate the relationship between blood serum 25-hydroxyvitamin D (25(OH)D) and UV exposure from two artificial sources. We then use the results to test the validity of the action spectrum for vitamin D production, and to infer the production from summer and winter sunlight. The results are based on a two-arm randomised clinical trial of biweekly UV exposure for 12 weeks using two different types of dermatological booths: one emitting primarily UV-A radiation, and the other emitting primarily UV-B radiation (booth A and booth B respectively). In terms of the vitamin D production per unit erythema, one of the booths mimics summer noon sunlight, while the other mimics winter noon sunlight. Blood samples were taken before and after the exposures. For all participants, the phototherapy booth treatments arrested the usual wintertime decline in 25(OH)D, and for most the treatments from either booth resulted in significant increases. The increases were highly non-linear and there was a high degree of variability in 25(OH)D and its response to UV from person to person. By the end of the 12 week period, the mean increase was >30 nmol l(-1) from a cumulative exposure of 17 SED from the UV-A booth, and twice that for the UV-B booth for which the cumulative exposure was 268 SED. Assuming a logarithmic relationship between UV and vitamin D, the results for the two booths show no obvious inconsistency in the action spectrum for pre-vitamin D production. However, further measurements with similar exposures from each booth are required to confirm its validity. A model was developed to describe the increases in serum 25(OH)D resulting from the UV exposures, which differed markedly between the two booths. The deduced initial rate of increase of 25(OH)D was approximately 5 nmol l(-1) per SED. From the large increases in 25(OH)D from each booth, along with knowledge of the spectral distribution of sunlight and assuming the currently-accepted action spectrum for photo-conversion to pre-vitamin D, we infer that the production of 25(OH)D from sunlight should be possible throughout the year, although in winter the exposures necessary to maintain optimal levels of 25(OH)D would be impractically long. This finding is at variance with the commonly-held view that no vitamin D is produced at mid-latitudes in the winter. Further work is needed to resolve that inconsistency.

Contribution of particulate nitrate to airborne measurements of total reactive nitrogen

[1] Simultaneous measurements of speciated, total reactive nitrogen (NOy) and particulate NO3 (particle diameter <1.3 mm) were made on board the NASA P-3B aircraft over the western Pacific in February–April 2001 during the Transport and Chemical Evolution over the Pacific (TRACE-P) experiment. Gas-phase and particulate NOy was measured using a gold tube catalytic converter. For the interpretation of particulate NOy, conversion efficiencies of particulate NH4NO3, KNO3, NaNO3, and Ca(NO3)2 were measured in the laboratory. Only NH4NO3 showed quantitative conversion, and its conversion efficiency was as high as that for HNO3 .N Oy measured on board the aircraft was found to be systematically higher by 10–30% than the sum of the individual NOy gas components ( P (NOy)i) at 0–4 km. Particulate NO3 concentrations measured by a particle-into-liquid

Horizontal propagation of large‐amplitude mountain waves into the polar night jet

We analyze a large amplitude mountain wave event, which was observed by a ground-based lidar above New Zealand between 31 July and 1 August 2014. Besides the lidar observations, ECMWF data, satellite observations and raytracing simulations are utilized in this study. It is found that the propagation of mountain waves into the middle atmosphere is influenced by two different phenomena at different times during the event. At the beginning of the event, convective instabilities cause wave breaking in the lower stratosphere. During the course of the event the mountain waves propagate to higher altitudes and are refracted towards the polar night jet due to the strong meridional shear of the zonal wind. As the waves propagate out of the observational volume, the ground-based lidar observes no mountain waves in the mesosphere. However, raytracing simulations and satellite observations indicate that the waves reached mesospheric altitudes downstream of New Zealand. These results underline the importance of considering horizontal propagation of gravity waves when analyzing locally confined gravity wave observations.

Long‐term variation of stratospheric aerosols observed with lidars over Tsukuba, Japan, from 1982 and Lauder, New Zealand, from 1992 to 2015

Vertical distributions of stratospheric aerosols have been measured with lidars over Tsukuba, Japan since 1982 and Lauder, New Zealand since 1992 to study the long-term and seasonal variations and influences of climate change. After volcanic eruptions of El Chichon in 1982 and Mt. Pinatubo in 1991, the vertically integrated stratospheric aerosol backscattering coefficient (IBC) increased to over 30 times the minimum level over the two sites. The IBC increased to more than twice the minimum over Tsukuba after volcanic eruptions in the northern high latitudes (Okmok, Kasatochi and Sarychev) and tropics (Nabro) between 2000 and 2011. Over Lauder, the IBC increased to more than twice the minimum after volcanic eruptions in the southern high latitudes (Puyehue-Cordon Caulle and Calbuco) and tropics (Kelud) between 2011 and 2015. The IBC showed seasonal variations with higher values in winter than in summer over the two sites. The mean radiative forcing by the stratospheric aerosols during the period 2000 − 2015 is estimated to be −0.15 ± 0.07 and −0.13 ± 0.06 Wm−2 over the two sites, which partially canceled the increase of global mean radiative forcing by CO2.

Two Methods for Retrieving UV Index for All Cloud Conditions from Sky Imager Products or Total SW Radiation Measurements

Cloud effects on UV Index (UVI) and total solar radiation (TR) as a function of cloud cover and sunny conditions (from sky images) as well as of solar zenith angle (SZA) are assessed. These analyses are undertaken for a southern‐hemisphere mid‐latitude site where a 10‐years dataset is available. It is confirmed that clouds reduce TR more than UV, in particular for obscured Sun conditions, low cloud fraction (<60%) and large SZA (>60°). Similarly, local short‐time enhancement effects are stronger for TR than for UV, mainly for visible Sun conditions, large cloud fraction and large SZA. Two methods to estimate UVI are developed: (1) from sky imaging cloud cover and sunny conditions, and (2) from TR measurements. Both methods may be used in practical applications, although Method 2 shows overall the best performance, as TR allows considering cloud optical properties. The mean absolute (relative) differences of Method 2 estimations with respect to measured values are 0.17 UVI units (6.7%, for 1 min data) and 0.79 Standard Erythemal Dose (SED) units (3.9%, for daily integrations). Method 1 shows less accurate results but it is still suitable to estimate UVI: mean absolute differences are 0.37 UVI units (15%) and 1.6 SED (8.0%).

Peak UV: Spectral contributions from cloud enhancements

We use multi-year datasets of UV spectral irradiances, measured to the exacting standards required by the Network for the Detection of Atmospheric Composition Change (NDACC), to investigate the enhancement effects of clouds and their wavelength dependence at sites that span a wide range of altitudes. These enhancements are derived by comparing weighted UV irradiance measurements with corresponding model calculations at each site for clear skies. We find that the frequency, magnitude, and wavelength-dependence of cloud enhancements are insufficient to explain the repeatedly high values of UVB and UVI observed by Cabrol et al., 2014, and that ozone amounts lower than have ever been seen there would be required.

How large and how long are UV and total radiation enhancements

Enhancement of solar radiation, which happens when solar irradiance at the surface is greater than the expected clear-sky value, is mainly caused by partial cloudy conditions. This effect has been extensively observed and investigated in the past, both on solar total radiation (TR) and on ultraviolet (UV) radiation. Characterization of the enhancements is relevant to better understand the radiative effects of clouds and solar radiation variability on the ground. We analyse this effect with a 10-years dataset obtained in Lauder, New Zealand, that contains TR and UV radiation measurements, cloud observations from a sky camera, and aerosol information from a four channel SPO2 solar-tracking radiometer, all at 1 min resolution. This great wealth of high-resolution measurements allows novel analyses and robust results about the typology of the radiation enhancements, in particular in terms of their duration, intensity and the associated atmospheric conditions.

Horizontal propagation of large amplitude mountain waves in the vicinity of the polar night jet

We analyze a large amplitude mountain wave event, which was observed by a ground-based lidar above New Zealand between 31 July and 1 August 2014. Besides the lidar observations, ECMWF data, satellite observations and raytracing simulations are utilized in this study. It is found that the propagation of mountain waves into the middle atmosphere is influenced by two different phenomena at different times during the event. At the beginning of the event, convective instabilities cause wave breaking in the lower stratosphere. During the course of the event the mountain waves propagate to higher altitudes and are refracted towards the polar night jet due to the strong meridional shear of the zonal wind. As the waves propagate out of the observational volume, the ground-based lidar observes no mountain waves in the mesosphere. However, raytracing simulations and satellite observations indicate that the waves reached mesospheric altitudes downstream of New Zealand. These results underline the importance of considering horizontal propagation of gravity waves when analyzing locally confined gravity wave observations.

25 years of solar spectral UV measurements at 45° S

We review 25 years of solar spectral UV at Lauder, measured to the exacting standards of the Network for the Detection of Atmospheric Composition Change (NDACC) with the best systems available at the time. Recent reanalysis of the alignment, calibration, and data processing from all nine of the UV spectroradiometers used at Lauder and other NDACC sites has better characterised the effects of changes in instrument technology. There has been no detectable trend in solar UV radiation other than that resulting from ozone variation.