Field measurements of sub-micron aerosol concentration during cold season in India

Sub-micron particle size distribution and temperature were measured at six levels immediately above the ground surface during 8-16 December 1997 and 24-28 December 1998. Diurnal observations were made at every three-hour interval at all the levels. Continuous measurements of aerosol concentration were made from 0300 to 1000 h at 1 m level. During this period, particle concentration decreases from 0300 h, attains a minimum value between 0600 and 0700 h, and then maximum at 0900 h. Particles 0.075 m show systematic variation in concentration, whereas particles < 0.075 m show large fluctuations with time during 0300 to 1000 h. Concentration of particles of sizes 0.075-0.75 m shows a minimum at 15-cm level where the temperature is maximum. However, particles of size 0.013 m undergo Brownian diffusion and thus do not show any trend with temperature. The phenomena of thermophoresis and fog scavenging are discussed in terms of these results

Atmospheric aerosol formation and its growth during the cold season in India

The effects of molecular diffusivity of H2SO4 and NH3 vapours on nucleated particles of SO2-4 and NO-3 species are reported. Condensation sink and source rate of H2SO4 and NH3 vapours, growth rates and ratios of real to apparent nucleation rates are calculated for SO2-4 and NO2-3 aerosols using fractional contributions of them in total aerosol size-distribution during the measurement period at Pune, reported in Chate and Pranesha (2004). The percentage of nucleated SO2-4and NO-3 aerosols of mid-point diameter 13 nm are 2 and 3 respectively of the total particles (13 nm Dp750 nm) for both H2SO4 and NH3 diffusion. In the diameter range 75 nm Dp 133 nm, it is 48 and 45 of SO2-4 and NO-3 aerosols, respectively for NH3 diffusion and 43 and 36 of SO2-4and NO-3 for H2SO4 diffusion. Increase in percentage of nucleated particles of these species corresponding to mid-point diameter 133 nm around 0900 h IST is significantly higher than that of mid-point diameter 13 nm and it is due to photo-chemical nucleation, coagulation and coalescence among nucleated clusters. The ratios of real to apparent formation rates for SO2-4 and NO-3 aerosols are 12 and 11 respectively, corresponding to mid-point diameter 13 nm, 17 and 13, for midpoint diameter 133 nm and 12 and 9.5, for mid-point diameter 750 nm. The results indicate that nucleation involving H2SO4 and acidic NH3 diffusion on SO2-4and NO-3 particles is the most relevant mechanism in this region

Diurnal Evolution of Urban Heat Island and Its Impact on Air Quality by Using Ground Observations (SAFAR) over New Delhi

The paper presents a study of urban heat island (UHI) intensity and its impact on air quality by using the System of Air Quality Forecasting and Research (SAFAR) network observations over Delhi during the clear sky month of December of 2013 and 2015. It is found that in the month of December 2013 and 2015 the UHI shows a peak in late evening around 20:00 hrs. The concentration of PM2.5 shows a bimodal peak in the month of December of both the years 2013 and 2015 which is due to the enhanced anthropogenic activity during the traffic hours. The formation of UHI during the late evening traffic hours is due to the enhancement in the concentration of PM2.5 due to the enhanced anthropogenic activity with higher ground heat flux and lower PBLH and wind speed which leads to both the years 2013 and 2015 during the month of December. It is also found that UHI intensity shows a positive correlation (r = 0.57) with PM2.5 concentration and a negative correlation (r = -0.40) with wind speed and the PM2.5 concentration also shows a negative correlation (r = -0.57) with wind speed during December 2013. Whereas during December 2015 it has found that UHI intensity has a positive correlation (r = 0.65) with PM2.5 concentration and a negative correlation (r = -0.45) with wind speed and the PM2.5 concentration also shows a negative correlation (r = -0.57) with wind speed

Variations in mass of the PM 10,PM 2.5 and PM 1 during the monsoon and the winter at New Delhi

PM10, PM2.5 and PM1 mass concentrations have been measured at Delhi (28°35'N; 77°12'E) during the August to December 2007. The running mean of PM10, PM2.5 and PM1 data shows large variations. The PM10, PM2.5 and PM1 were ranged from 20 to 180 μg/m3 during the monsoon and from 100 to 500 μg/m3 during the winter (up to 1200 μg/m3 in November due to Deepavali fireworks). For the same running mean cycles, higher mass concentrations in the PM10, PM2.5 and PM1 were corresponded with peaks in the relative humidity and lower levels linked to peaks in the ambient temperature. The evolutions of PM10, PM2.5 and PM1 concentrations after the elapsed times are simulated with mean mass scavenging coefficients. These evolution patterns clearly show the difference in washout of PM10 with impaction scavenging relative to those for PM2.5 and PM1 particles over different rainfall durations. Air-mass pathways traced with HYSPLIT model over the study area illustrates the nature of PM10, PM2.5 and PM1 levels with monsoon and winter air-mass circulations over Delhi

Seasonal variation of urban heat island and its impact on air-quality using SAFAR observations at Delhi, India

This paper discussed the urban heat island (UHI) intensity and local air quality by using observational data of project of the System of Air Quality Forecasting and Research (SAFAR) over Delhi during the month of May and December 2013. It is found that UHI magnitudes ~2.2°C and ~1.5°C are formed at the evening traffic hours during May and December respectively. Also, intensity of UHI < 0°C over daytime is referred as Urban Cool Island (UCI) during May and December. The diurnal PM2.5 concentration shows a bimodal pattern with peaks at morning and evening traffic hours during May and December. The planetary boundary layer height (PBLH) values show higher in magnitude during the daytime and lower in magnitude during the night-time. Whereas, the Ground Heat Flux values are lower during the daytime and higher during the night-time. The wind speed shows lower values during the UHI and higher magnitudes during the UCI formation hours. Concentration of PM2.5 and wind speed shows a strong negative correlation during May (r = -0.56, p = 0.002) and December (r = -0.57, p = 0.001) at C V Raman (CVR) site, however, high values in the concentration of PM2.5 during the low wind speed favour the condition for the formation of UCI. The regression analysis indicated that PM2.5 plays a significant role in the daytime cooling and nighttime warming over the urban areas during the low wind speed condition

Assessments of PM1, PM2.5 and PM10 concentrations in Delhi at different mean cycles

ABSTRACT Daily, monthly, seasonal and annual moving means of PM1, PM2.5 and PM10 concentrations from August, 2007 to October, 2008 at Delhi (28� 35' N; 77� 12' E), the seventh populous megacity in the world are presented. PM1, PM2.5 and PM10 concentrations varied seasonally with atmospheric processes and the anthropogenic activities. PM10 decreases during monsoon by ~25-80 �g m-3 and PM1 and PM2.5 by ~10-15 �g m-3 from their pre-monsoon levels. Emissions from fireworks during Deepawali in the post-monsoon season increases PM1, PM2.5 and PM10 levels by 300, 350 and 400 �g m-3, respectively over their monsoon levels. Seasonal variation of mixing heights, temperatures, winds and rainfall, accounts for the inter-annual variability of PM1, PM2.5, and PM10. Accordingly, wintertime PM1, PM2.5 and PM10 components contribute by ~30-33% to annual levels. PM10 in summer is higher by 8% to that of PM2.5 and by 9% to that of PM1. PM10 components in post-monsoon are lower by 5% to that of PM2.5 and by 7% to that of PM1. Also, PM1, PM2.5 and PM10 levels were higher during October, 2008 than those in 2007, but their levels were almost remain the same in August and September of 2007 and 2008. Moving means of PM1, PM2.5 and PM10 and their concentrations in different seasons are useful in policy making decisions thereupon aiming to improve the air quality in Delhi

Impact of emission mitigation on ozone-induced wheat and rice damage in India

In this study, we evaluate the potential impact of ground level ozone (O3) on rice and wheat yield in top 10 states in India during 2005. This study is based on simulated hourly O3 concentration from the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), district-wise seasonal crop production datasets and accumulated daytime hourly O3 concentration over a threshold of 40 ppbv (AOT40) indices to estimate crop yield damage resulting from ambient O3 exposure. The response of nitrogen oxides (NOx) and volatile organic compounds (VOC) mitigation action is evaluated based on ground level O3 simulations with individual reduction in anthropogenic NOx and VOC emissions over the Indian domain. The total loss of wheat and rice from top 10 producing states in India is estimated to be 2.2 million tonnes (3.3%) and 2.05 million tonnes (2.5%) respectively. Sensitivity model study reveals relatively 93% decrease in O3-induced crop yield losses in response to anthropogenic NOx emission mitigation. The response of VOC mitigation action results in relatively small changes of about 24% decrease in O3-induced crop yield losses, suggesting NOx as a key pollutant for mitigation. VOC also contribute to crop yield reduction but their effects are a distant second compared to NOx effects

Sink mechanism for significantly low level of ozone over the Arabian Sea during monsoon

Measurement of surface ozone over the Arabian Sea during the southwest monsoon season (June-September) of 2002 has shown an unusually low level of ozone with an overall average of 9 nmol/mol. Such a low level of ozone could not be explained by simulations using a three-dimensional chemistry transport model, Model for Ozone and Related Tracers (MOZART), which accounts for the known processes of advective transport and includes a standard photochemical mechanism. Thus, for the Arabian Sea region, we propose for the first time that destruction of ozone by reactive halides released from sea salt aerosols is the sink mechanism which played a crucial role in ensuring the significantly low ozone level over the Arabian Sea. Theoretical calculations constrained by observations have shown that, on average, ozone losses due to catalytic action of halogens and due to photolysis plus chemical reaction amount to 2.15 nmol mol-1d-1 and 4.64 nmol mol-1d-1, respectively

Air Pollution, Air Quality and Climate Change (Editorial)

The introduction of gases and particulate contaminants in the atmosphere due to natural or human activities causes air pollution. The concentration and toxicity of these contaminants define air quality and in the long term contribute to climate change. Both air pollution and climate change influence each other through complex interactions in the atmosphere. This issue has 9 very interesting manuscripts, touching various aspects of air pollution and air quality and their impact on climate change

Air pollution, air quality, and climate change

The introduction of gases and particulate contaminants in the atmosphere due to natural or human activities causes air pollution. The concentration and toxicity of these contaminants define air quality and in the long term contribute to climate change. Both air pollution and climate change influence each other through complex interactions in the atmosphere. This issue has 9 very interesting manuscripts, touching various aspects of air pollution and air quality and their impact on climate chang